Essentials for Survival

The human nervous system is a very important part of the body that helps us think, move, feel, and react to things around us. It works like a control centre, sending and receiving messages throughout the body. In this topic, you will learn about the two main parts of the nervous system which are the central nervous system (CNS) and the peripheral nervous system (PNS). The central nervous system is made up of the brain and spinal cord while the peripheral nervous system links the rest of the body to the brain and spinal cord. You will also explore how some body actions happen automatically, like breathing and heartbeat, through another part called the autonomic nervous system. Finally, you will understand how messages travel through the body using special cells called neurons.

KEY IDEAS

• Autonomic Nervous System: Controls involuntary actions like heartbeat and breathing.

• Brain: Processes information and sends instructions. It acts as the command centre for the central nervous system

• CNS: Made up of the brain and spinal cord; controls most body functions.

• Nerve impulses: Electrical signals that carry messages through neurons.

• PNS: Links the CNS to the rest of the body through nerves.

• Spinal Cord: Sends messages between brain and body, controls reflexes.

The nervous system controls your actions. It is made up of neurons or nerve cells, coordinating different parts of your body so that they can work together and be able to bring about the correct responses.

The nervous system is commonly divided into two parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

Meaning of Nervous system The nervous system is like the body’s control centre and messaging system which helps us to think, move, feel things and even do things we are not aware or curious of, like breathing and blinking of the eye. The system is made up of two main parts;

1. The Central Nervous system CNS) and

2. The Peripheral Nervous system. (PNS) The Central Nervous System (CNS) The central nervous system (CNS) consists of the brain and the spinal cord acting as the main processing centre for information.

The brain tissue is protected by the bony skull, and the spinal cord is protected by the backbone or the vertebrae. Nerves link the brain and spinal cord to the rest of the body.

The spinal cord and the brain consist of white and grey matter.

In the spinal cord, the white matter is at the surface with the grey matter inside, but this pattern is reversed in the brain of mammals, the grey matter lying on the outer surface, while white matter lies beneath it.

Components of Central nervous System (CNS) and their functions The Brain The brain is the body’s most complex organ, weighing about 3 pounds and controlling vital functions (breathing, heart rate), sensory processing, emotions, and cognition. It acts as the command centre for the central nervous system, utilizing billions of neurons to regulate, think, and store memories. The brain must be healthy for the body to work properly. The outer surface of the cerebrum (the largest part of the brain) is called the cerebral cortex, and it is made of grey matter, which contains nerve cell bodies and fibres that help send and receive messages. Inside the cerebrum, is white matter, which is made of fibres covered with a protective layer called myelin. These fibres help carry messages quickly between parts of the brain.

The main parts of the brain are the

1. Forebrain (Cerebrum)

2. Midbrain

3. Hindbrain (Cerebellum)

4. Medulla Oblongata

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Figure 3.1: A diagram of the human brain

1. Cerebrum (Forebrain) The cerebrum is the largest part of the human brain, and it is divided into two halves called the left and right cerebral hemispheres. These hemispheres are separated by a deep groove known as a fissure. Each hemisphere is further divided into four main lobes that can be seen from the outside: the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe.

Functions of the Cerebral cortex or Cerebrum

a. The cerebrum helps us learn new things and store information.

b. It allows us to use intelligence and solve problems.

c. It interprets sensory information, such as what we see, hear, feel, taste, and smell.

d. It controls voluntary movements of our muscles.

e. It is responsible for thinking, imagination, and reasoning.

f. It stores memories and controls emotions.

g. It helps us develop new skills and coordinate body movements.

h. It plays a role in shaping our personality.

i. It controls important functions like speech, vision, taste, smell, and touch.

The cerebrum also has other important parts that help control different body functions and mental processes.

A. Hypothalamus B. Pituitary gland A. Hypothalamus: The hypothalamus is a small but very important part of the brain located just below the thalamus. It controls many body functions by producing hormones and directing the pituitary gland to maintain homeostasis (internal stability).

Functions of the Hypothalamus

i. Helps the body keep the right balance of water and salts.

ii. Checks the level of carbon dioxide in the blood.

iii. Controls and maintains normal body temperature.

iv. Regulates when we sleep and wake up.

v. Controls hunger, thirst, and body weight.

vi. Helps to control heart rate and blood pressure.

B. Pituitary Gland: The pituitary gland, also called the “master gland,” is found at the base of the brain just below the hypothalamus. It produces hormones that regulate many body functions and also control other endocrine glands.

Functions of pituitary hormones

i. Help the body grow physically.

ii. Regulate the balance of water in the body.

iii. Stimulate and control the activities of other endocrine glands.

iv. Control sexual development and metabolism.

2. Midbrain The midbrain is a small part of the brain found between the forebrain and the hindbrain. It contains nerve fibres covered with myelin and centres for visual and hearing reflexes.

Functions of the midbrain

1. Controls eye movement.

2. Coordinates head movement in response to light and sound.

3. Processes sound information.

3. Hindbrain The hindbrain is made up of the cerebellum and the medulla oblongata. It acts as the command centre for essential survival functions (acting as the body’s autopilot) A. Cerebellum: Also referred to as “little brain” the cerebellum receives information from the inner ear and muscles to help the body stay balanced and maintain posture. Drinking too much alcohol can disturb its function.

Functions of the cerebellum

i. Maintains posture and balance.

ii. Coordinates voluntary movements such as walking, running, or driving.

iii. Helps to maintain normal muscle tone.

B. Medulla Oblongata: The medulla oblongata lies below the cerebellum and connects the brain to the spinal cord. It controls many involuntary activities of the body.

Functions of the medulla oblongata

i. Controls heart rate and breathing.

ii. Regulates blood pressure.

iii. Manages reflexes such as coughing, sneezing and yawning.

iv. Controls swallowing and vomiting.

Functions of the Central Nervous System (CNS)

₁. Controls human emotional behaviour.

2. Manages all reflex and conditioned reflex actions.

3. Coordinates the body’s response to changes in the environment (e.g., regulating body temperature when external temperature changes).

4. Receives information from all parts of the body through sensory neurons, interprets it, and sends the correct response through motor neurons to effectors such as muscles and glands.

Causes of Failure of the Nervous System (Brain and Spinal Cord) ₁. Psychological conditions (e.g., depression): Mental health problems such as depression and anxiety can change brain structure and function. Stress and depression may reduce neurotransmitter levels, shrink brain areas like the hippocampus (important for memory), and affect thinking. Long-term stress may also increase the risk of brain diseases such as Alzheimer’s.

2. Substance abuse (e.g., Indian hemp, heroin): Drugs and alcohol can damage the brain.

Prolonged use of substances like marijuana, heroin, cocaine, and methamphetamine changes how the brain works, affecting memory, thinking, and self-control. Some drugs lower oxygen supply to the brain, killing cells and increasing the risk of strokes.

Alcohol abuse may cause Wernicke-Korsakoff syndrome, a brain disorder linked to vitamin B1 deficiency.

3. Mental Illness and Sexually Transmitted Infections (STIs)

a. Disease that gets worse over time. The brain or nerves are being damaged slowly by some disease over time. For a example Alzheimer’s disease, this cause memory loss, Parkinson disease affects movement, multiple sclerosis affects how nerves send signals.

b. Tumours, an outgrowth of cell into a lump. This in the brain or spinal cord can press vital organs and stop them from working well

c. Additionally, sexually transmitted infections (STIs) such as syphilis and HIV can damage the nervous system. Neurosyphilis affects the brain and spinal cord, leading to cognitive decline and movement disorders. HIV-associated neurocognitive disorders (HAND) occur when the virus damages brain cells, leading to difficulties in memory, concentration, and coordination.

4. Physical trauma (e.g., Motor vehicle and domestic accidents): Traumatic injuries from accidents or physical abuse can cause permanent damage to the brain and spinal cord. A traumatic brain injury (TBI) may result from falls, blows to the head, or car accidents, leading to loss of cognitive function, impaired speech, and personality changes. Spinal cord injuries from severe impacts can result in paralysis, loss of sensation, and difficulty in motor function. The severity of these injuries often depends on the location and extent of the damage.

The Spinal Cord

The spinal cord is a soft, white, rope-like structure that runs inside the backbone. It begins from the medulla oblongata in the brain and extends through the length of the vertebral column. The backbone protects the spinal cord from injury. At its centre, the spinal cord has a canal called the central canal, which is filled with cerebrospinal fluid.

The spinal cord has two main parts: the inner grey matter and the outer white matter. The grey matter contains nerve cells (neurons) and surrounds the central canal, giving it a grey colour. The white matter contains nerve fibres, which give it a whitish appearance.

On the surface of the spinal cord, there are two grooves: one at the back called the dorsal fissure, and one at the front called the ventral fissure.

The spinal cord has 31 pairs of spinal nerves connected to it. The sensory nerves enter the spinal cord through the dorsal (back) roots, carrying information like touch, heat, and pain towards the brain. The motor nerves leave the spinal cord through the ventral (front) roots, carrying instructions from the brain to the muscles and glands.

In addition, there are side parts of the spinal cord called the lateral columns, which carry both sensory and motor information. These are called mixed nerves.

Figure 3.2: A diagram of the spinal cord.

Functions of the Spinal Cord

The spinal cord serves as a vital communication and coordination centre within the central nervous system.

1. The spinal cord receives information from different parts of the body through sensory nerves. These nerves carry messages about things like pain, heat, pressure, or touch into the back part of the spinal cord. From there, the information is sent to the brain so it can be understood.

2. The spinal cord also sends instructions from the brain to the body. Motor nerves carry these messages from the front part of the spinal cord to muscles and glands. This allows the body to move or for glands to release substances.

3. The spinal cord controls reflex actions. Reflexes are quick, automatic responses to stimuli, and do not need the brain’s help. For example, when you touch something hot, your hand pulls away immediately. This fast response helps to protect the body from harm.

In a group of at least 5 members. Write down your findings on what happened when you get an itch on your elbow.

Activity 3.1 Transmission of Nerve Impulses

What to do Study the following step-by-step description of how the body responds to an itchy elbow, and then answer the questions that follow

1. Receptors in your skin detect an itch on your right elbow

2. The receptors send a message along sensory neurons to the spinal cord

3. The message is sent up to the brain, telling it what is happening

4. The brain receives a message about the itchy skin

5. The brain decides to scratch your elbow with your left hand, it sends a message back down the spinal cord

6. The message is sent to the muscle in your hand and arm from the central nervous system down the motor neuron

7. The muscle moves your hand and arm to scratch the itchy skin.

Key questions

1. Identify the stimulus in the reaction.

2. What is the response?

3. Which part of the body is the receptor, the effector, and the coordinator?

Activity 3.2 Building your personal CNS model Aim: Create a model of your nervous system to understand its structure and functions What you need

• Three different coloured modelling clay or playdough

• Cardboard base (size of a book)

• Toothpicks and small labels

• Measuring tape or ruler

• Mirror

• Notebook for observation What to do

Step 1: Build your Cerebrum

1. Take pink/red clay and form a large oval shape (about 8cm long)

2. Draw a line down the middle; this separates the left and right hemispheres

3. Mark the four lobes with toothpicks

a. Frontal lobe (front): Where you think and plan

b. Parietal lobe (top): Where you feel touch

c. Temporal lobe (sides): Where you hear and remember

d. Occipital lobe (back): Where you process vision Self-Test: Point to each lobe on your model and explain what it does.

a. Build your cerebellum

i. Take yellow clay and make a smaller round shape (3cm diameter)

ii. Add ridges with a pencil to show it is folded

iii. Place behind your cerebrum

iv. Label: “Balance and coordination” Stand on one foot while looking at your model. Your cerebellum is working to keep you balanced!

b. Build your brain stem

i. Take brown clay and make a cylinder (4cm long, 2cm wide)

ii. Connect to the bottom of the cerebrum

iii. Label three parts

• Midbrain (top): Eye movement

• Pons (middle): Sleep regulation

• Medulla oblongata (bottom): Breathing and heart rate Self-Test: Count your heartbeats for 15 seconds. Your medulla oblongata controls this automatically.

Step 2: Build your spinal cord

1. Take the remaining brown clay and roll it into a long rope (12cm)

2. Attach to the bottom of the brain stem

3. Make small marks every 2cm to show segments

4. Add small clay pieces sticking out - these are nerve branches.

Self-Test: Feel along your spine from neck to lower back. This is where your spinal cord runs.

Step 3: Test CNS functions Cerebrum tests

1. Frontal lobe: Solve this math problem: 25 + 17 =?

2. Parietal lobe: Close your eyes and touch your nose

3. Temporal lobe: Listen to sounds around you for 30 seconds

4. Occipital lobe: Look at your model and identify the colours Cerebellum tests:

1. Walk in a straight line heel-to-toe for 10 steps

2. Touch your nose with alternating hands (eyes closed)

3. Stand on one foot for 30 seconds

Activity 3.3 Exploring functions of CNS Aim: To get familiarised with the functions of the central nervous system.

What to do

1. In a group of 6 (3 pairs), conduct research into functions of different parts of the central nervous system, e.g.

a. The cerebral cortex in cognition

b. The spinal cord in reflexes

c. The brainstem in the regulation of vital functions

2. Discuss your findings as a group and with members of other groups.

3. Using your findings as a prompt, conduct a role-play scenario whereby each of the group members represents a different part of the CNS. Be creative with this task, considering how you will demonstrate how signals are processed in the CNS.

4. Perform your role-play to one other group.

Peripheral Nervous System

The peripheral nervous system (PNS) is made up of nerves that extend from the central nervous system (CNS) to the rest of the body. It serves as a communication network connecting the brain and spinal cord to the organs, muscles, and skin. The PNS has two main parts: the cranial nerves, which come from the brain (to handle sensory, motor or mixed functions, primarily controlling head, neck and facial sensations, muscle movement and involuntary autonomic functions like digestion) and the spinal nerves, which come from the spinal cord (they facilitate voluntary movement, sensory perception like pain and touch as well as manage involuntary functions like heartbeat and sweat gland activity).

Functions of the Peripheral Nervous System

₁. Carrying sensory information such as vision, smell, and hearing to the brain.

2. Controlling motor actions such as movements of the tongue, eyes, jaw, and lips.

3. Relaying information between the CNS and the body’s organs and limbs.

Example: When you touch a hot object, the PNS quickly sends a message to the spinal cord and brain (CNS), which then sends a signal back through the PNS to move your hand away Read the scenario below and try answering the questions that follow.

In a group of 3-5 members, discuss the question below and write down your answer in your notebook.

Emmanuel is a final-year student to give a speech at the national science fair. As he walks onto the stage, he starts to feel very nervous. His heart beats faster, his hands get sweaty, and he breathes more quickly. These changes happen automatically because his body is reacting to stress.

Once Emmanuel starts speaking and sees the audience smiling and clapping, he begins to feel more confident. His heart rate slows down, his breathing becomes normal, and he feels more relaxed. This happens because his body is calming down with the help of the nervous system, which controls how the body reacts in different situations.

After the speech, Emmanuel goes backstage. Someone gives him a hot drink in a cup. As he reaches for it, the cup slips a little in his hand. Without thinking, he quickly grabs it tighter and stops it from falling.

Emmanuel sits down and takes a sip of the warm drink. He feels proud of his speech and thankful for how his body helped him through it, from being nervous at first, to calming down and even reacting quickly to stop an accident.

a. Analyse the role of the autonomic nervous system in Emmanuel’s physiological changes before, during, and after his speech.

b. Support your answer with specific references to both the sympathetic and parasympathetic nervous systems.

Consider this: You step out onto the porch of your house, and suddenly your eyes widen;

what? A snake! It is lying in the corner close to the wall. At the sight of it, a sudden chill runs through your body because you know snakes can be very dangerous. Instantly, without even thinking, you react in one of two ways. You either run away in fear or you gather courage and quickly look for a stick, stone, or anything you can use to kill the snake.

But here is the big question: What makes you choose whether to run (flight) or to fight?

Let us explore this together.

Note

• Autonomic Nervous System controls involuntary actions such as breathing and heartbeat and includes the sympathetic (triggers fight or flight by raising heart rate, blood pressure or dilating pupils) and parasympathetic (promotes rest and digest by lowering heart rate and stimulating digestion) systems. The sympathetic system mobilises energy for stress response, while the parasympathetic system conserves energy (resting state).

• Motor nerves carry instructions from the CNS to muscles and glands, enabling movement and response.

• Peripheral Nervous System (PNS) connects the central nervous system to the rest of the body and enables communication between the brain, spinal cord, and organs.

• Sensory nerves carry information to the CNS from sense organs like the skin, eyes, and ears.

• The Somatic Nervous System controls voluntary actions such as walking, writing, or picking up objects.

The Peripheral Nervous System (PNS)

The Peripheral Nervous System (PNS) includes all the nerves found outside the brain and spinal cord. It connects the central nervous system (CNS); which is the brain and spinal cord, to the rest of the body.

The PNS is made up of ₁. Spinal nerves: They are arranged in 31 pairs and carry messages to and from the spinal cord.

2. Cranial nerves: They are arranged in 12 pairs and carry messages directly between the brain and different parts of the body, without going through the spinal cord.

Together, these nerves help the brain and spinal cord communicate with the body, allowing us to move, feel, and respond to the environment.

Spinal nerves emerge bilaterally from the spinal cord. These points of exit are the dorsal and ventral horns of the spinal cord. The ventral portion of a spinal nerve is responsible for transmitting information away from the CNS to effector organs like muscles and glands (that act in response to a nerve impulse or stimulus); this is known as efferent function.

Due to its role in controlling skeletal muscle movement, the ventral portion of the nerve is also commonly referred to as a “motor” nerve. On the other hand, the dorsal portion of the spinal nerve is afferent, meaning it carries sensory information towards the CNS. In summary, afferent axons provide sensory input to the CNS, while efferent axons enable the CNS to send motor commands to muscles, internal organs, and glands.

Types of the Peripheral Nervous System (PNS)

The peripheral nervous system (PNS) is organised into two main subdivisions: the somatic nervous system and the autonomic nervous system.

1. Somatic Nervous System (SNS)

The somatic nervous system is part of the peripheral nervous system that controls both sensing and movement. The sensory nerves in this system carry information from the skin (like pain and temperature) and from the muscles to the central nervous system (CNS).

This allows us to be aware of what is happening around us. The motor nerves carry instructions from the CNS to the skeletal muscles. This makes it possible for us to move our bodies voluntarily, such as walking, writing, or lifting objects. In short, the somatic nervous system helps us sense the environment and make voluntary movements in response.

2. Autonomic nervous system (ANS) The autonomic nervous system (ANS) regulates the body’s internal environment. It does this through a network of sensory and motor neurons that connect the central nervous system (especially the hypothalamus and medulla oblongata) to internal organs such as the heart, lungs, and both exocrine and endocrine glands. The autonomic nervous system (ANS) constantly monitors internal conditions and makes necessary changes to maintain homeostasis.

Motor neurons in the autonomic nervous system control the movement of smooth muscles (found in the walls of internal organs) and cardiac muscles (in the heart). Motor neurons in the autonomic nervous system control the movement of smooth muscles (found in the walls of internal organs) and cardiac muscles (in the heart).

In contrast to the somatic system, the actions of the autonomic nervous system are largely involuntary. Another important difference is that the autonomic nervous system (ANS) uses two neurons linked in a chain to send messages to organs, while the somatic system uses only one motor neuron.

Figure 3.3: Peripheral nervous system The autonomic nervous system (ANS) controls the body’s internal environment without us thinking about it. It works through special sensory and motor nerves that connect the brain (especially the hypothalamus and medulla oblongata) to organs such as the heart, lungs, and glands.

The ANS is always checking the inside of the body and making changes to keep things balanced (homeostasis). It controls smooth muscles in the walls of internal organs and the cardiac muscle of the heart, helping to regulate functions like heartbeat, breathing, and gland activities.

Effector Tissues of ANS

These tissues are the targets of the ANS and are responsible for carrying out its functions.

There are three types, which are

1. Smooth muscle: Found in the walls of blood vessels, the digestive tract, and other organs, smooth muscle contractions are controlled by the ANS.

2. Cardiac muscle: The heart muscle, responsible for pumping blood, is also regulated by the ANS.

3. Glandular tissues: The ANS controls the secretions of various glands, including salivary glands, sweat glands and digestive glands.

Figure 3.4: Types of effector tissues for ANS Sympathetic and Parasympathetic Nervous Systems The autonomic nervous system (ANS) has two main branches: the sympathetic and parasympathetic systems. The sympathetic and parasympathetic systems act on the same organs but in opposite ways. The sympathetic system prepares the body for “fight or flight,” like when you are scared or in danger. It increases heart rate, breathing, and energy supply.

On the other hand, the parasympathetic system helps the body rest, relax, and save energy.

Figure 3.5: Sympathetic and parasympathetic nerves.

1. Sympathetic nervous system In this system, there is a short nerve (called a preganglionic nerve) that comes from the brain or spinal cord and connects to a small group of nerve cells called a ganglion, which is located near the spinal cord.

At the ganglion, this first nerve releases a chemical called acetylcholine (ACh). This chemical passes the message to the next nerve (called the postganglionic nerve), which is usually long and thin.

The postganglionic nerve then carries the message all the way to a body part (like the heart). When it gets there, it releases another chemical (hormone) called norepinephrine (NE). This chemical attaches to special receptors on the body part (called alpha and beta receptors) to cause a specific response; like making the heartbeat faster.

The effects of norepinephrine release include

a. Stimulation of heartbeat, increasing heart rate.

b. Elevation of blood pressure.

c. Dilation of the pupils of the eyes.

d. Dilation of the trachea and bronchi, increasing airflow to the lungs.

e. Stimulation of glycogenolysis, the breakdown of liver glycogen into glucose, providing energy.

f. Shunting of blood away from the skin and viscera (internal organs) towards skeletal muscles, the brain, and the heart, prioritizing oxygen delivery to these critical areas.

g. Inhibition of peristalsis in the gastrointestinal (GI) tract, slowing down digestion.

h. Inhibition of contraction of the bladder and rectum, delaying elimination.

The sympathetic nervous system helps the body get ready to face or escape danger, a reaction often called “fight or flight.” This wide response happens in two main ways. First, one preganglionic neuron can connect with many postganglionic neurons, spreading the signal to several organs at once. Second, the adrenal glands release adrenaline (epinephrine) into the blood, carrying the message to almost all cells in the body, even those not directly connected to sympathetic nerves.

Figure 3.5: Sympathetic nervous system.

2. Parasympathetic nervous system This part of the autonomic nervous system is called the parasympathetic system. It has long preganglionic nerves that come from the brain or spinal cord and travel to small groups of nerve cells (ganglia) that are very close to or inside the organ they control.

At the ganglia, the first nerve releases a chemical called acetylcholine (ACh), which passes the message to the postganglionic nerve. This second nerve is short and carries the message to the target organ (like the heart).

When the message reaches the organ, the second nerve releases ACh again, but this time it connects to muscarinic receptors on the organ. These receptors decide how the organ responds, such as slowing the heart rate or helping digestion.

Parasympathetic stimulation generally produces effects that are opposite to those of the sympathetic system, promoting a “rest-and-digest” state:

a. Slowing down of the heartbeat, decreasing heart rate.

b. Lowering of blood pressure.

c. Constriction of the pupils of the eyes.

d. Increased blood flow to the skin and viscera, supporting digestion and other restorative processes.

e. Stimulation of peristalsis in the gastrointestinal (GI) tract, promoting digestion.

Figure 3.6: Parasympathetic nervous system Balance between the sympathetic and parasympathetic nervous systems ₁. The sympathetic and parasympathetic nervous systems work together to keep the body balanced and healthy (a state called homeostasis).

2. The sympathetic system helps the body get ready for action in stressful situations. It increases your heart rate, breathing, and blood pressure; this is called the “fight-or- flight” response.

3. The parasympathetic system helps the body calm down and recover after the stress. It slows the heart rate, lowers blood pressure, and helps with digestion; this is called the “rest-and-digest” response.

4. Both systems take turns depending on what your body needs at the moment, helping you stay safe, calm, and healthy.

Figure 3.7: Balance between sympathetic and parasympathetic activity

Table 3.1: Difference between somatic and autonomic nervous systems Somatic Nervous System Autonomic Nervous System Works voluntarily (under conscious control) Works involuntarily (automatic, not under conscious control) Controls skeletal muscles Controls smooth muscles, heart muscles, and glands Has only one motor neuron Has two motor neurons (preganglionic and postganglionic) Uses acetylcholine as the neurotransmitter Uses acetylcholine or norepinephrine as the neurotransmitter Always causes stimulation (excitatory) Can either stimulate (excitatory) or slow down (inhibitory) Controlled mainly by the cerebrum Controlled mainly by the brain’s centres (pons, hypothalamus, medulla) Voluntary Action Voluntary actions are activities that we can control. They can be started or stopped at any time by our choice. These actions are controlled by the brain (cerebrum).

Examples: walking, singing, eating, swimming, dancing, jumping, kicking a ball, and throwing a stone.

Involuntary Actions

Involuntary actions are activities that happen in the body without our control. They occur automatically, even if we do not notice them. Most are controlled by the spinal cord or brainstem, not the conscious brain.

Examples: heartbeat, breathing, blinking, dilation of pupils, salivation when smelling food, regulating body temperature, and dilation/constriction of blood vessels.

Table 3.2: Comparison of involuntary and voluntary actions Involuntary Actions (Spinal Reflex) Voluntary Actions Controlled by the spinal cord, not under conscious control Controlled by the forebrain, under conscious control Impulse travels only in the spinal cord Impulse travels from the brain down the spinal cord A nerve impulse takes the shortest path A nerve impulse takes a longer path Response is immediate Response can be delayed Response can be in skeletal or internal involuntary muscles The response is only in skeletal muscles Perform this activity in a group of no more than 8 members.

Activity 3.4 Role-playing PNS

Aim: To understand how the Peripheral Nervous System (PNS) works What you need

1. Labels or paper to show your role

2. A small object (like a ball or chalk) to represent a message What to do

1. Form a group of 8 learners. Assign each person one of the following roles:

a. Brain

b. Spinal Cord

c. Sensory Neuron 1

d. Sensory Neuron 2

e. Motor Neuron 1

f. Motor Neuron 2

g. Skin

h. Muscle

2. Use your creativity to act out this situation: “A person touches something hot.”

3. Act it out step-by-step

a. The Skin feels the heat and passes the message (object) to Sensory Neuron 1.

b. Sensory Neuron 1 passes it to Sensory Neuron 2.

c. Sensory Neuron 2 sends it to the Spinal Cord.

d. The Spinal Cord sends the message to the Brain.

e. The Brain thinks and sends a command back to the Spinal Cord.

f. The Spinal Cord sends it to Motor Neuron 1, then to Motor Neuron 2.

g. Motor Neuron 2 gives it to the Muscle, which reacts by pretending to pull the hand away.

4. Each group member must say their role aloud when they pass the message (e.g., “I am the motor neuron. I send the command to the muscle!”).

5. After the Role Play

a. Draw a simple diagram in your books showing the path the message took.

b. Write one sentence each to explain your role.

Activity 3.5 Study and recreate a diagram of the PNS

1. Ensure that you label your diagram in a detailed manner, including;

2. The key components, such as nerves, ganglia and sensory receptors

3. The functions of the somatic and the autonomic nervous systems

4. Examples of voluntary and involuntary actions

5. A comparison of the roles of the sympathetic and parasympathetic systems Present your work to a few of your peers.

Activity 3.6 Nature walk Go for a walk around your local area and allow yourself to notice all of the sensory experiences that you are getting. What can you smell, hear, feel, see, taste?

When you get back to the classroom, give an example of each of these senses being stimulated and explain how the PNS facilitates these experiences.

Let’s build upon what we have already learnt about voluntary and involuntary actions. You might have, at some point, accidentally touched a hot cooking pot, heater or pressing iron;

stepped on a sharp pin, iron nail or bone or had your knee touched suddenly. In each case, you reacted in a way that you did not initiate. What about the giggles that take you over as you are being tickled? All of these reactions of your body to the stimuli above do not come from the brain. Together, they are called reflex action.

Let us find out more about reflex action.

Notes

• Reflex Action: A reflex action is a fast, automatic, and involuntary response to a stimulus without conscious thought.

• Functions of Reflexes: Reflexes help protect the body from harm, allow quick reactions to danger, and maintain homeostasis.

• Importance of Reflexes: Reflexes are crucial for survival, support bodily functions like blinking and breathing, and reduce reaction time in emergencies.

• Reflex Arc Structure: A reflex arc is the pathway followed by nerve impulses during a reflex action, involving a receptor, sensory neuron, relay neuron, motor neuron, and effector.

• Types of Neurons in Reflexes: Reflex actions involve sensory neurons (carry impulses to the CNS), relay neurons (process the information), and motor neurons (carry impulses to muscles or glands).

Reflex action A reflex action is a quick and automatic response to something that happens in or around the body. It does not involve thinking or decision-making.

The idea of reflexes was first explained by a scientist named Marshall Hall in the 1800s.

He compared reflexes to how a ball bounces back when thrown against a wall; the body “reacts” quickly to a stimulus.

Reflex actions are natural and happen through the central nervous system (CNS) without involving the brain for conscious thought. For example, when you touch something hot, you quickly pull your hand away without thinking.

Examples of Reflex Actions

₁. The pupil of the eye dilates or constricts when exposed to light of different intensities.

2. Sudden withdrawal of the hand or leg when pricked by a pin.

3. Coughing or sneezing caused by irritants in the nasal passage.

4. Knee-jerk reaction when the knee is tapped or stamped on.

5. Immediate withdrawal of the hand when it touches a sharp object.

6. Sudden blinking of the eyes when an insect comes very close.

7. Quick withdrawal of the hand from a hot object.

8. Watering (tearing) of the eyes when something falls into them.

9. The flow of breast milk when a baby sucks the mother’s nipple.

10. Withdrawal of the leg when stepping on a sharp object.

A Reflex Arc

A reflex arc is the path that nerve impulses follow during a reflex. Some critical components which form the reflex arc are receptor organs, sensory neurons, nerve centres, associated neurons, motor neurons, and effector neurons. The stimuli are perceived by the receptor organs. Afferent neurons, also known as sensory neurons, transport stimuli from receptors to the spinal cord. The sensory neurons are found in the spinal cord’s ganglion. The nerve centre, where synaptic connections are formed, is the spinal cord. Motor neurons are found in the ventral horn of the spinal cord. The glands and muscles that respond to stimuli are known as effector organs.

A simple reflex arc is summarised as follows

1. A receptor detects a stimulus (e.g., heat from a hot object).

2. A sensory neuron transmits the signal from the receptor to the central nervous system (spinal cord).

3. The sensory neuron connects with a motor neuron in the integration centre.

4. The motor neuron carries the signal from the integration centre to an effector.

5. The effector, which is either a muscle or gland that carries out the response (e.g., muscle contraction to move the hand away).

Figure 3.8: A reflex arc Neurons and their Role in Reflexes Most reflex arcs use only three neurons. Neurons are special nerve cells that are designed to carry electrical messages (impulses) from one part of the body to another. They are very important in reflex actions because they quickly link the sensory organs, spinal cord, muscles, and glands.

Neurons make up the main nervous tissue in animals (except simple ones like sponges and placozoa). Plants and fungi do not have nerve cells.

Each neuron has

a. A cell body: contains the nucleus and processes information.

b. Dendrites: branch-like parts that receive information and carry it to the cell body.

c. Axon: a long fibre that carries impulses away from the cell body to the axon terminals (end plates).

d. Myelin sheath: a fatty layer around the axon that insulates it and speeds up the message.

e. Nodes of Ranvier: small gaps in the myelin sheath that allow impulses to travel faster along the axon.

Figure 3.9: Structure of a neuron.

Classification of Neurons

Structurally, neurons can be put into the following classes based on the location of the cell body and the number of morphological processes emerging out of it:

a. Unipolar neuron: This is characterised by a single process extending from the cell body, which then splits into two branches, one acting as a dendrite and the other as an axon.

b. Pseudo-unipolar neuron: This is characterised by a single axon that splits into two branches shortly after emerging from the cell body.

c. Bipolar neuron: This is characterised by two processes, one axon and one dendrite extending from opposite sides of the cell body.

d. Multipolar neuron: This is characterised by one axon and multiple dendrites extending from the cell body.

Figure 3.10: Classes of neurons.

Types of Neurons

Functionally, there are three types of neurons. These are

1. Sensory neuron

2. Relay neuron/Inter-neuron

3. Motor neuron

1. Sensory Neurons: They are also known as afferent neurons, and are nerve cells that convert stimuli from the environment (such as light, sound and pain) into electrical signals (action potentials) and transmit them to the central nervous system for processing.

They use a process called sensory transduction to convert stimuli detected through sensory receptors into action potentials

Figure 3.11: A sensory neuron

2. Relay Neuron/Inter-neuron: Relay neurons are only found in the central nervous system (the brain and spinal cord) and connect a sensory neuron to a motor neuron to facilitate reflex actions and complex processing. They are also referred to as associated neuron or intermediate neuron.

Figure 3.12: A relay/inter-neuron

3. Motor neurons: They are typically multipolar and their axon is often myelinated.

They transmit signals from the central nervous system (brain and spinal cord) to muscles and glands, enabling movement and other bodily functions (voluntary and involuntary).

It is also known as efferent neurons (since they carry impulses away from the central nervous system).

Figure 3.13: A motor neuron

Activity 3.7 Investigation Reflex Action

What you need

• Reflex hammer (or use your hand)

• Chair or bench

• Stopwatch (optional)

• Volunteer learner What to do

1. Ask the volunteer to sit with their legs hanging freely.

2. Locate the patellar tendon below the kneecap.

3. Gently tap the tendon with the reflex hammer.

4. Observe the leg’s automatic kick (knee-jerk reflex).

5. Repeat to compare reflex strength between both legs.

Discussion and analysis

1. Discuss with a few peers whether the body’s response is voluntary or involuntary. Can the volunteer stop it from happening if they concentrate really hard?

2. Analyse/discuss the differences between voluntary and involuntary actions.

3. Create a concept map and/or an illustration to demonstrate the pathway of nerve impulses/reflex arcs.

Figure 3.14: Reflex action

Activity 3.8 Research Neurological Disorders Affecting Neuron Function

Using the internet and any other resources available, investigate one neurological disorder or abnormality which affects neuron function. Create a short summary of the nature of abnormality and of the way in which it affects sufferers. Discuss treatments and management strategies.

Role Of Reflexes in Daily Life

Reflex actions are crucial for survival in the following ways:

1. Protection

a. Avoiding Injury: Reflexes like withdrawing a hand from a hot or sharp object or blinking when something approaches the eye prevents potential injuries.

b. Maintaining Balance: Reflexes help maintain posture and balance, such as automatically adjusting limb position when you trip or stumble.

2. Movement and coordination

a. Basic Motor Skills: Reflexes, like the stepping reflex in infants, form the foundation for more complex movements like walking.

b. Coordination: Reflexes help coordinate movements, allowing for smooth and efficient actions like catching a ball or avoiding obstacles.

3. Homeostasis: Reflexes contribute to maintaining a stable internal environment, such as shivering to generate heat when cold.

4. Adaptation: Reflexes allow the body to adapt to changing conditions, like adjusting pupil size in different light intensities.

In this section we will analyse the transmission of nerve impulses in further detail. The human body contains specialised cells called neurons, which are responsible for transmitting electrical signals; known as nerve impulses; throughout the body at high speeds.

These nerve impulses play a crucial role in enabling various functions, such as movement, sensation, memory, and perception. Whether it is feeling pain, enjoying the taste of food, or recalling important information, nerve impulses allow the brain to communicate effectively with different parts of the body in real time.

Note

• Neurotransmitters are chemical messengers that allow communication between neurons across synapses and can excite or inhibit the receiving neuron.

• Nerve impulses are electrical signals generated by changes in voltage across the neuron’s membrane (action potentials) and travel along axons, especially fast in myelinated neurons.

• Synapses connect neurons through structures like axon terminals, synaptic clefts, and receptor sites, enabling one-way signal transmission.

• Synaptic transmission involves neurotransmitter release triggered by calcium ions, binding to receptors, and signal termination through reuptake or breakdown.

• Synapses perform vital functions such as integrating signals, directing signal flow, filtering weak stimuli, and supporting memory and behaviour.

• Neurons sum inputs through temporal and spatial summation, using excitatory (EPSP) and inhibitory (IPSP) signals, and can be modulated by chemicals that adjust their responsiveness.

Neurotransmitters Neurotransmitters are special chemical messengers made by nerve cells (neurons) that enable neurons to communicate with each other, muscles or glands, controlling functions like movement, mood, sleep and heart rate. They are stored in small sacs called synaptic vesicles located at the end of a neuron (in the terminal buttons).

When a neuron is activated and sends an electrical signal (action potential), it causes these vesicles to release the neurotransmitters into a small gap between two neurons called the synaptic cleft.

The neurotransmitters then travel across this gap and attach to receptors on the surface of the next cell. This cell could be another neuron, or an effector cell, like a muscle or gland.

This process allows messages to pass from one cell to another, helping the body respond quickly and accurately to changes inside or outside the body (like muscle contraction or mood regulation). It is an essential part of how the nervous system works.

So far, scientists have discovered more than 100 different types of neurotransmitters. New ones are still being found as researchers learn more about how the brain and nervous system function.

Types of Neurotransmitters and Their Effects

Neurotransmitters affect how messages are passed between nerve cells. They can have two main effects on the next neuron (called the postsynaptic neuron)

1. Excitatory neurotransmitters These increase the chance that the next neuron will send a signal (called an action potential), boosting activity in the brain.

Examples of excitatory neurotransmitters

a. Acetylcholine (ACh): Helps with muscle movement, learning, memory, and REM sleep.

b. Glutamate: The most common excitatory neurotransmitter in the brain. Important for learning and brain flexibility (also called neural plasticity).

c. Catecholamines: Dopamine and norepinephrine: Help with mood, alertness, focus, and body movement.

d. Serotonin: Affects mood, appetite, and sleep.

e. Histamine: Helps keep us awake and plays a role in immune system responses.

2. Inhibitory Neurotransmitters

These reduce the chance that the next neuron will send a signal. They help calm the brain and prevent overactivity.

Example: GABA (gamma-aminobutyric acid): The main inhibitory neurotransmitter in the brain. It relaxes the nervous system and prevents overstimulation.

3. Dual-Function Neurotransmitters

Some neurotransmitters can be either excitatory or inhibitory, depending on:

a. The type of receptor they attach to.

b. The situation in the body.

Example: Dopamine: It can excite or inhibit depending on the receptor type (like D1 vs.

D2).

Table 3.3: Neurotransmitters and their functions Neurotransmitters Functions Acetylcholine (ACh) Affects movement, learning, memory, and REM sleep Gama-Aminobutyric Acid (GABA) Facilitates neural inhibition in the central nervous system (too much action potential), it is the brain’s chill pill-it calms neurons, reducing

activity and promoting relaxation, sleep, as well as lowering anxiety.

Endorphins Provide relief from pain and promote feelings of pleasure and well- being. It acts like the body’s natural painkillers Dopamine (DA) Controls voluntary movements of the body and affects movement, attention, learning, reinforcement, and pleasure. It acts like the brain’s reward chemical Norepinephrine (NE) Affects eating, alertness, and wakefulness. It boosts energy and focus. Acts as the alert system Epinephrine aka Adrenaline Affects the metabolism of glucose, energy release during exercise and stress. Triggers the fight or flight response Serotonin (5HT) Affects mood, sleep, appetite, impulsivity, and aggression. It is like a mood stabiliser Neurotransmitter Release When a nerve signal (called an action potential) reaches the end of a neuron (the presynaptic terminal), it causes the membrane to change (depolarise). This opens calcium channels, and calcium ions (Ca²+) enter the neuron. The calcium ions make small sacs called synaptic vesicles move and join with the cell membrane. These vesicles then release neurotransmitters into the gap between neurons (called the synaptic cleft); this process is called exocytosis.

Once released, the neurotransmitters travel across the synaptic cleft and attach to special receptors on the next cell (the postsynaptic membrane). These receptors can be Ligand- gated ion channels (they open to let ions in or out). G protein-coupled receptors (they start slower, longer-lasting effects inside the cell).

Postsynaptic Effects

₁. If the neurotransmitter opens channels that let positive ions in, the cell becomes more likely to fire (called depolarisation or EPSP).

2. If it opens channels for negative ions, the cell becomes less likely to fire (called hyperpolarisation or IPSP).

3. G protein-coupled receptors (cell surfaces that detect signals and activate internal responses) may affect the cell in other ways, such as changing enzyme activity or turning on/off genes.

How the Signal Stops (Neurotransmitter Inactivation)

Once the message is sent, the neurotransmitter must be removed so the cell can reset. This happens in three main ways:

a. Reuptake: The neurotransmitter is taken back into the original neuron or nearby support cells.

b. Enzymatic Breakdown: Special enzymes break down the neurotransmitter in the synaptic cleft.

c. Diffusion: The neurotransmitter simply moves away from the synapse into surrounding areas.

Neurotransmission Neurotransmission is the fundamental process by which neurons communicate with each other and with effector cells (like muscle or gland cells) across synapses. It involves the generation and propagation of electrical signals within neurons and the conversion of these electrical signals into chemical signals that cross the synaptic gap.

Generation and Propagation of Nerve Impulses

A nerve impulse is an electrical signal that travels along a neuron (nerve cell). It allows the nervous system to send messages quickly between the brain, spinal cord, and other parts of the body.

1. Resting Potential (Before the Impulse)

When a neuron is not sending a signal, it is said to be at resting potential. The inside of the neuron is negatively charged compared to the outside. This is because there are more sodium ions (Na+) outside the cell and more potassium ions (K+) and negatively charged proteins inside. The resting potential is about -70 millivolts (mV). It is like the ready state of the neuron, primed and waiting to trigger an action potential.

2. Action Potential (Impulse Generation)

Nerve impulses, also known as action potentials, are quick electrical signals that travel along a nerve cell (neuron).

a. Depolarisation (Starting the Signal): When a stimulus (like a chemical message from another neuron) reaches a nerve cell, it causes the inside of the cell to become less negative. If this change reaches a certain level (called the threshold), special gates in the cell membrane open and let sodium ions (Na+) rush into the cell. This makes the inside of the cell more positive, and more gates open in a positive feedback loop. The membrane potential can rise to about +30 millivolts (mV). Depolarisation triggers the action potential (more like the spark that sparks the fire)

b. Repolarisation (Resetting the Signal): Very soon after, the sodium gates close, and potassium gates open. Potassium ions (K+) move out of the cell, making the inside more negative again. This step helps bring the nerve cell back toward its resting state.

c. Hyperpolarisation (Brief Extra Reset): The potassium gates stay open a little too long, which makes the cell even more negative than usual. This is called hyperpolarisation. After this, the cell returns to its normal resting potential, ready to send another signal

3. Transmission of the Impulse Along the Neuron

The action potential travels along the axon like a wave. As it moves, it opens ion channels in the next part of the axon, continuing the signal. This process is called propagation.

4. Saltatory Conduction (Faster Transmission)

In myelinated neurons, the impulse jumps between gaps in the myelin sheath called Nodes of Ranvier. This makes the impulse travel much faster. This type of transmission is called saltatory conduction.

Regulation and Integration of Neural Signalling

Neurons receive input from multiple other neurons at synapses on their dendrites and cell bodies. These inputs can be excitatory (depolarizing) or inhibitory (hyperpolarising):

a. Excitatory postsynaptic potentials (EPSPs): Depolarisations that increase the likelihood of the postsynaptic neuron firing an action potential.

b. Inhibitory postsynaptic potentials (IPSPs): Hyperpolarisations that decrease the likelihood of the postsynaptic neuron firing.

Temporal and Spatial Summation

The postsynaptic neuron integrates these inputs through temporal summation (adding up EPSPs or IPSPs that occur close together in time) and spatial summation (adding up EPSPs or IPSPs that occur simultaneously at different locations on the neuron). If the combined effect of the inputs depolarizes the postsynaptic neuron to the threshold, an action potential is generated at the axon hillock and propagates along its axon.

Neuromodulator: In addition to fast synaptic transmission, neuromodulators can regulate neuronal activity. Neuromodulators are chemicals that don’t directly excite or inhibit neurons but instead modify the strength of synaptic transmission or the excitability of neurons. They can act over longer distances and time scales than neurotransmitters.

Synapse A synapse is the small gap between two nerve cells (neurons) where messages are passed from one neuron to the next.

Structure of a Synapse

₁. Presynaptic Neuron (Sender): This is the neuron that sends the message.

a. Axon terminal: The end of the neuron that connects to the next cell.

b. Synaptic vesicles: Tiny bubbles that carry neurotransmitters (the chemicals that carry the message).

c. Calcium channels: Let calcium in when a signal arrives. This helps release the message.

d. Mitochondria: Provide energy to the cell.

2. Synaptic Cleft (The Gap): A tiny space between the two neurons (about 20–40 nanometers wide). The message (neurotransmitters) jumps across this gap to reach the next neuron.

3. Postsynaptic Neuron (Receiver): This is the neuron that receives the message.

Receptors: Special proteins that catch the neurotransmitters. When the receptors catch the chemical signal, a new electrical signal is made in the receiving neuron.

Figure 3.15: Synaptic transmission Functions of synapse ₁. Synapses in the CNS: In the central nervous system (CNS), synapses usually connect one neuron to another. These connections allow neurons in the brain and spinal cord to communicate, making learning, memory, and control of body functions possible.

2. Synapses in the PNS: In the peripheral nervous system (PNS), the postsynaptic cell can be another neuron or an effector cell like a muscle or gland. For example:

a. At neuromuscular junctions, neurons connect to muscles, causing them to contract.

b. At neuroglandular junctions, neurons connect to glands, leading to secretion of substances such as hormones.

3. One-way communication: Nerve impulses at synapses always travel in one direction;

from the presynaptic neuron to the postsynaptic cell. This ensures that messages move in an organized way through the nervous system.

4. Filtering signals: Synapses can strengthen or weaken signals. Weak signals may be blocked so they do not activate the postsynaptic neuron, while strong signals that reach the threshold are passed on. This helps the brain focus on important information and ignore unimportant noise.

5. Role of neurotransmitters: Neurons communicate at synapses by releasing chemicals called neurotransmitters. These chemicals carry messages that control movement, feelings, perception, and thinking. If synapses do not work properly, it can lead to conditions such as depression, anxiety, epilepsy, or Alzheimer’s disease.

6. Integration of signals: One neuron can receive signals from hundreds of others.

Synapses help the neuron combine (integrate) these signals—some exciting, some stopping activity; and then decide whether to send a new signal. This process is important for decision-making in the brain.

7. Threshold for action: For a signal to cross a synapse, it must be strong enough to trigger an action potential (about +40 mV). If the signal is too weak, it will not pass on. This prevents the brain from being overloaded with weak or irrelevant information and allows attention to focus on important events like a loud noise or bright light.

Synaptic Transmission

Synaptic transmission is the process by which a signal is transmitted from one neuron to another or to an effector cell across a synapse. The CNS contains more than 100 billion neurons. The brain has 86 billion neurons. Some CNS neurons receive 20,000 synapses.

How Nerve Impulses Move Across a Synapse

When a nerve impulse (action potential) reaches the end of a neuron (called the terminal or axon terminal), it causes calcium (Ca²+) channels in the membrane to open. As a result, calcium ions enter the neuron from outside.

This calcium triggers tiny sacs called vesicles (which contain neurotransmitters) to move toward the edge of the neuron. These vesicles fuse with the membrane and release neurotransmitters into the gap between two neurons. This gap is called the synaptic cleft.

The neurotransmitters then move across the synaptic cleft and attach to receptor sites on the next neuron (called the postsynaptic neuron). This triggers a response in the postsynaptic neuron:

a. If the neurotransmitter is excitatory (like glutamate), it causes sodium (Na+) channels on the next neuron to open. Sodium flows in, causing the inside of the neuron to become more positive. If the signal is strong enough, it creates a new nerve impulse in the next neuron.

b. If the neurotransmitter is inhibitory (like GABA), it may open potassium (K+) or chloride (Cl–) channels. Potassium may flow out or chloride may flow in, making the inside of the neuron more negative, and making it harder for an impulse to start.

Figure 3.16: Synaptic Transmission

What Happens to Extra Neurotransmitters?

Not all neurotransmitters bind to receptors. The extras are removed in two ways:

1. Reuptake: The sending neuron takes them back for reuse.

2. Enzymatic breakdown: Special enzymes break them down. For example, acetylcholinesterase breaks down acetylcholine. These clean-up steps keep the synapse ready for the next signal.

Figure 3.17: Reuptake of Neurotransmitters

Effect of Drugs Like Cocaine

Some drugs can interfere with this process. For example, cocaine blocks the reuptake of dopamine (a feel-good neurotransmitter). This causes dopamine to stay longer in the synapse and overstimulate the next neuron. That is why cocaine causes strong feelings of pleasure; but it also makes it highly addictive.

Activity 3.9 Modelling Nerve Impulse Generation

Aim: To understand generation and transmission of nerve impulses What you need

• 10 dominoes or rectangular bars

• Ruler or meter stick

• Stopwatch

• Coloured tape (red, blue, green)

• Labels and markers

• Notebook for recording What to do Part A: Resting Potential Setup Create Your Neuron Model

1. Arrange 10 dominoes in a straight line, spaced 2cm apart

2. Label the setup

a. Red tape: Mark the first domino as “Stimulus point”

b. Blue tape: Mark dominoes 2-9 as “Axon”

c. Green tape: Mark the last domino as “Axon terminal”

3. Record initial state

a. All dominoes standing represent Resting potential (-70mV)

b. System is ready to receive stimulus Understanding resting potential

a. Standing dominoes represent the neuron at rest

b. Negative charge inside the neuron (more K+ inside, more Na+ outside)

c. Stable state until stimulus arrives Part B: Action Potential Generation (15 minutes) Stimulus Application

a. Gently push the first domino (stimulus point)

b. Start the stopwatch as soon as you push

c. Observe the chain reaction as dominoes fall in sequence

d. Stop timing when the last domino falls Record your observations

a. Time for complete transmission: _____ seconds

b. Speed of transmission: Distance ÷ Time = _____ cm/second

c. Pattern observed: Describe how the “impulse” travelled Analyse the Process Domino 1 (Stimulus point)

a. Depolarisation: Domino falls represent Na+ channels open

b. Threshold reached: -55mV equivalent Dominoes 2-9 (Axon)

a. Propagation: Each falling domino triggers the next

b. All-or-nothing: Each domino falls completely or not at all

c. Unidirectional: Signal travels in one direction only Domino 10 (Axon terminal)

a. Signal arrives: Ready for synaptic transmission

b. Calcium channels open: Prepares for neurotransmitter release Reset and Repeat

a. Stand all dominoes up represents repolarisation and return to resting potential

b. Repeat the experiment 3 times

c. Calculate average transmission time Part C: Factors Affecting Transmission Speed Experiment with variables Test 1: Spacing Effect (Myelination)

a. Increase spacing to 4cm between dominoes

b. Time the transmission again

c. Compare speeds: Wider spacing results to faster transmission (like myelinated neurons) Test 2: Obstacle Effect (Damage)

a. Place a small obstacle between dominoes 5 and 6

b. Observe what happens to signal transmission

c. Analyse: How does this relate to nerve damage?

Figure 3.18: Dominoes or rectangular bars

Activity 3.10 Research Task on an Aspect of Neurotransmission Objective: Explore the fundamental processes of neurotransmission, focusing on how neurons communicate across synapses to transmit signals within the nervous system.

Choose One of the Following Focus Areas

a. Steps of neurotransmission: synthesis, storage, release, receptor binding, and termination.

b. Major neurotransmitters (e.g., glutamate, GABA, dopamine, serotonin, acetylcholine) and their roles.

c. The difference between excitatory and inhibitory signalling.

d. Mechanisms of synaptic plasticity and their importance in learning and memory.

e. How disruptions in neurotransmission contribute to neurological and psychiatric disorders.

What to do Produce a brief summary of your chosen area, including labelled diagrams where appropriate.

Activity 3.11 Neuron Simulation

Click on the link below and spend some time becoming familiar with the PHeT simulation about neurons. Experient with changing variables and observing the effects.

Neuron 1.1.34

1. Analyse what happens in your CNS when you ride a bicycle.

2. If someone had damage to their cerebellum, what difficulties would they experience?

3. A patient has a spinal cord injury that affects both somatic and autonomic functions

a. Differentiate between the somatic and autonomic symptoms that might occur.

b. Explain why some reflexes might still work below the injury level.

c. Analyse the challenges this creates for homeostasis.

d. Discuss how the body might compensate for lost autonomic control.

Scenario On her way home from school, Fatima suddenly heard the screeching of tyres. In an instant, she jumped back onto the sidewalk, narrowly avoiding a speeding motorcycle. She later noticed her heart racing, her hands trembling, and her breathing becoming faster. Fatima realised she had not made a conscious choice to move; her body had reacted automatically.

Her biology teacher used this incident as a case study and challenged the class to investigate what had happened inside Fatima’s body. Learners were asked to examine her response as a reflex action, compare it with voluntary movement, and explain why reflexes are essential for survival.

4. Analyse the sequence of events in Fatima’s response and identify the following.

a. The stimulus

b. The sensory neuron

c. The interneuron (relay neuron)

d. The motor neuron

e. The effector (muscle or gland)

5. A postsynaptic neuron receives the following inputs simultaneously:

3 excitatory inputs (each +2 mV) 2 inhibitory inputs (each -3 mV) Threshold = +3 mV Analyse the information given and do the following.

a. Calculate the net effect on the postsynaptic neuron

b. Determine if an action potential will be generated

c. Explain how this demonstrates synaptic integration

d. Predict what would happen if one more inhibitory input were added

The human body relies on the skeleton and muscles to give it shape, protect vital organs, and make movement possible. In this lesson, we will study the musculoskeletal system, which includes the bones, muscles, joints, and connective tissues that work together to support the body. The lesson will examine how the human skeleton is structured and how it works with muscles to produce movement. You will also learn about the three main types of muscle tissues found in the human body. Skeletal muscles are attached to bones and help us make voluntary movements such as walking or writing. Smooth muscles are located in the walls of internal organs like the stomach and intestines; they control involuntary actions such as digestion. The third type, cardiac muscle, is found only in the heart and helps to pump blood throughout the body continuously. Through observation, modelling, and classroom discussions, you will gain a deeper understanding of how the bones and muscles depend on each other. You will explore how they work together to produce movement, maintain body posture, and protect delicate organs such as the brain, heart, and lungs. By the end of this lesson, you should be able to explain how the musculoskeletal system supports life and

activity in the human body.

KEY IDEAS

• The axial and appendicular skeletons form the two main divisions of the human skeleton.

• The skeletal system is made up of bones, joints, and connective tissues such as cartilage and ligaments.

• The human skeleton performs several important functions, including support, movement, protection of internal organs, and production of blood cells.

• The main parts of the human skeleton include the skull, vertebral column, rib cage, and limbs.

• There are different types of skeletal systems found in living organisms, such as exoskeletons, endoskeletons, and hydrostatic skeletons.

Hello, learners. Have you ever come across the bone remains of a dead animal? Have you wondered what those bones were doing in the body of the animal and the parallels between that and our own bodies? This week, we are embarking on a trip into the human body to study its bony framework known as the skeletal system.

Skeletal material The skeletons of animals are made of three types of materials. These are:

1. Chitin: It is the major component of the skeleton of arthropods. It is a tough, light and flexible material. Chitin is made of carbohydrate (cellulose) and strengthened by deposits of hardened proteins and minerals. Organisms whose skeleton is made of chitin include crustaceans (crabs, lobsters, shrimp) and arachnids (spiders, scorpions)

2. Cartilage: Cartilage is made of living cells (called chondroblasts), carbohydrates and protein fibres. It is a tough and flexible tissue that has great tensile strength. It acts as a shock absorber and protects bones from rubbing against each other during movement. The skeleton and entire system of sharks, rays, skates and foetuses are made of cartilage: In humans, cartilage occurs in the ear, nose, discs between the vertebrae of the vertebral column, trachea, bronchi, epiglottis and the Eustachian tube.

Cartilage does not have its own blood supply vessels but depends on the oxygen and nutrients that diffuse across nearby tissues.

There are three types of cartilage. These are hyaline cartilage, fibro-cartilage and elastic cartilage.

3. Bone: Bones are hard, living connective tissue that provide structural support, protect organs, facilitate movement and store minerals like calcium. It is composed of compact and spongy tissue and contains specialised cells (osteoblasts, osteocytes, and osteoclasts) that constantly build, maintain, and reshape the tissue through a process called bone remodelling.

Activity 4.1 Identifying cartilage Aim: To identify cartilage through touch.

What to do

1. Individually, feel your ears by probing them gently with your hands.

2. Repeat by doing the same to your nose.

3. Touch other body parts such as lips, cheeks, neck and arms. Can you find any other areas which feel similar to the ears and nose, and are therefore made of cartilage?

4. Record your observations and findings.

Discussion

1. Discuss your observations and findings in small groups of four and share ideas with other groups.

2. List all structures in the human body made of cartilage for a class discussion.

Types of skeletons The main types of skeletons in animals are Endoskeleton, Exoskeleton and Hydrostatic Skeleton.

1. Endoskeleton This is an internal structure which mainly provides support in all vertebrates. It is primarily composed of bones and cartilage. Bones are living, dynamic tissues that constantly build, maintain, and reshape themselves. This process is called bone remodelling. Bones are generally hard and strong. This hardness and strength come mainly from the presence of calcium salts, which are mineral substances, in them. The presence of calcium compounds in bones makes them rigid and capable of supporting body weight. Where two bones meet in the body (such as in the hip, knee, or elbow joint), their contacting surfaces are covered with a pad of cartilage (also known as gristle).

The function of this cartilage pad is to

1. Reduce friction between bones during movement.

2. Act as a shock absorber to prevent damage from impact.

Examples of vertebrates with endoskeletons include the following listed below.

1. Mammals such as cows, rats, humans, rabbits and bats.

2. Reptiles such as snakes, lizards and crocodiles.

3. Bony fish such as tilapia.

4. Birds.

Figure 4.1: Some vertebrates with an endoskeleton.

2. Exoskeleton This is a hard, external covering mainly composed of chitin. It protects and supports the bodies of some invertebrates, particularly arthropods. It is made of a tough, flexible polysaccharide that resembles cellulose. Animals with this type of skeleton undergo periodic moulting or shedding of their exoskeleton in a process called ecdysis in order to grow. This happens because exoskeletons are rigid and non-expandable, which, if not shed, will not allow growth of the animal to take place.

Examples of animals that have exoskeletons include spiders, crabs, lobsters, millipedes, centipedes, houseflies, cockroaches, butterflies, and beetles.

Figure 4.2: Some invertebrates with exoskeleton.

3. Hydrostatic skeleton This type of skeleton is found in soft-bodied invertebrates. Such animals rely on the pressure of internal fluid to maintain shape and enable movement. The skeleton consists of a fluid-filled cavity surrounded by muscles. When muscles contract around the cavity, the incompressible fluid inside the cavity provides rigidity and support, allowing the animal to move or maintain its form. Examples of animals with hydrostatic skeletons include earthworms, maggots, jellyfish, and sea anemone.

Figure 4.3: Some soft invertebrates with a hydrostatic skeleton.

Let us do the following activity to find out how the different kinds of skeletons help living organisms. Do this in a group of four members.

Activity 4.2 Investigating Skeletons

Aim: To explain how different skeletons support movement, protect, and ensure survival across different species and environments.

What to do: In a group of 6 learners, split into pairs and research the functions of different types of skeletons (endoskeleton, exoskeleton and hydrostatic skeleton).

Consider the following questions.

1. How does this kind of skeleton support movement?

2. How does it protect the animal?

3. How does it ensure survival?

Discussion: Write down your findings and discuss them among yourselves and with the other pairs in your group. Use your findings to prepare a chart of the three types of skeletons. Present your chart for class discussion and critique and arrange them for a gallery walk.

Functions of the mammalian skeleton ₁. Structural framework: It gives the body its basic shape and structure.

2. Body shape: It helps to define the physical form and posture.

3. Support: It holds up the body and keeps it upright.

4. Protection: The skull protects the brain, the ribcage shields the heart and lungs, and the vertebrae protect the spinal cord.

5. Surfaces for muscle attachment: Bones have projections and ridges (called facets) where muscles attach to facilitate movement.

6. Movement: Bones, in combination with muscles and joints, allow for complex movement.

7. Blood cell formation: The bone marrow, found in the central cavities of certain bones, produces red blood cells, white blood cells, and platelets in a process called haematopoiesis.

8. Stores minerals: Bones serve as reservoirs for important minerals, particularly calcium and phosphorus, which can be released into the bloodstream when needed.

Key question: Consider a human body without a bony skeleton. How do you think such a body could function?

Structure and Composition of Bone

Bone is a living connective tissue made up of both organic and inorganic components, giving it a unique combination of strength, rigidity, and lightness.

It consists of;

1. Living bone cells known as osteocytes.

2. Protein fibres primarily collagen, which provide flexibility and tensile strength.

3. Mineral salts, mainly calcium phosphate and calcium carbonate, which provide hardness and rigidity.

Approximately two-thirds of the bone mass is made up of inorganic mineral salts (non- living), while one-third consists of organic materials (living cells and protein fibres).

Unlike cartilage, bone has its own blood supply, which allows for active nourishment, growth, and repair. This vascularisation (the physiological process of developing new blood vessels to deliver oxygen and nutrients) makes bone a dynamic tissue that can remodel and heal when damaged Ossification (Bone formation) The process of ossification refers to the development of bone tissue and the deposition of minerals, such as calcium phosphate and calcium carbonate, into a tissue matrix, replacing cartilage or fibrous tissue to form hardened bone. Ossification occurs during foetal development, growth in children and adolescents, fracture healing, and throughout life as part of bone remodelling.

There are two types of ossification

1. Intramembranous ossification: Where bone develops directly from mesenchymal (embryonic connective) tissue, e.g., in flat bones of the skull.

2. Endochondral ossification: Where bone forms by replacing cartilage (e.g., in long bones like the femur).

Structure of a Long Bone

A long bone, such as the femur (the longest and strongest bone in the body that connects the hip to knee) or humerus a long bone in the upper arm connecting the shoulder to elbow), in humans has two distinct regions. These are:

1. Compact bone: This makes up the hard outer shaft (diaphysis). It is dense and strong and contains Haversian systems (osteons). These are structural units made of concentric rings of bone matrix (lamellae). The lamellae are arranged around Haversian canals.

Osteocytes (bone cells) are located in small spaces called lacunae. Tiny channels, called canaliculi, connect lacunae, allowing nutrients and waste to pass between osteocytes and nearby capillaries.

2. Spongy/cancellous bone: This makes the expanded ends of the bone (epiphyses).

It has a honeycomb-like structure with numerous bony struts called trabeculae. It contains red bone marrow within its spaces, which produces blood cells. Despite its porous appearance, it is well-adapted to withstand compressive forces.

Bone marrow: This is a soft spongy tissue found inside larger bones. There are two types, namely, red bone marrow and yellow bone marrow. Red bone marrow, also known as myeloid tissue, is found in the spongy bone of the epiphyses. It contains haematopoietic (blood-forming) stem cells that constantly produce new red blood cells, white blood cells, and platelets. Yellow bone marrow, which is composed mostly of fat, is contained in the medullary cavity of the shaft. It contains mesenchymal stem cells that can develop into cartilage, fat, or bone cells.

Figure 4.4: Structure of a long bone Adaptation of bone structure Structurally, a bone is designed to possess the following adaptations

1. Light but strong: Ideal for mobility and support.

2. Ability to withstand stress and pressure: Achieved through the strategic arrangement of trabeculae in spongy bone to resist compression forces.

3. Ability to exchange nutrients and waste: Takes place via vascular and neural access through bone canals and pores.

Parts Of the Mammalian Skeleton

The mammalian skeleton consists of the following major parts;

a. Skull

b. Vertebral column.

c. Limbs and limb girdles.

Figure 4.5: The human skeleton

Activity 4.3 Cutting and building a human skeleton model Aim: Identify various parts of the human skeleton.

What you need: Pictures of the human skeleton printed on manila cards.

page1.pdf

a. Cutters such as knives and pairs of scissors.

b. Needle and thread to sew cut parts together.

What to do

1. In a group of five, cut out the skeleton on the card.

2. Using the needle and thread, each member sews together the cut pieces.

3. Each member would be expected to mount their model for the identification of the various parts.

4. Label your skeleton with the names of the major bones, joints and the locations of any known muscles.

Precaution: Care must be taken in perforating the card with the needle in order not to dismember the cut parts.

There are two main divisions. These are axial and appendicular skeletons.

Axial Skeleton

The axial skeleton forms the central axis of the body and consists of the following parts

a. Skull

b. Vertebral column (Backbone or spine)

c. Ribs and sternum (Breastbone) This is the body’s main frame Skull: The skull is a bony structure composed of several separate bones formed by intramembranous ossification. It protects the brain and houses vital senses – eyes, ears, nose and mouth. The bones can be divided into those of the cranium and those of the face.

The cranial bones are flattened and thick and are fused by immovable joints called sutures.

Key among the facial bones are the upper jawbone (maxilla) and lower jawbone (mandible).

In humans, the maxilla is movable and is used for biting and chewing food.

The cranium (braincase) protects the brain, while facial bones provide cavities (orbits) to house and protect the eyes and structures that protect the ears and nose.

Figure 4.6: Human braincase and facial bones Vertebral Column (Backbone or Spine): This runs along the dorsal (back) side of vertebrates.

In humans, it starts from the base of the skull and ends at the pelvis (sacrum). In mammals with a tail, it ends in caudal vertebrae, which extend to form the tail.

The vertebral column is composed of individual bones called vertebrae. These are joined end to end to form a flexible, protective tube which houses the spinal cord. Between each pair of vertebrae are intervertebral discs made of cartilage and fibrous tissue. These act as shock absorbers and allow flexibility and movement.

The vertebral column provides support for the body during various kinds of movement, attachment for muscles, and protection for the spinal cord.

There are five main groups of vertebrae in humans and most mammals. These are shown in

Table 4.1 below.

Table 4.1: Groups of vertebrae in humans, number of vertebrae and their locations.

Group of vertebrae Number Location Function

1. Cervical vertebrae 7 Neck region Balancing the head supports head movement and protects the spine

2. Thoracic vertebrae 12 Chest/thoracic region Attaching to the ribs and forms the chest cavity.

3. Lumbar vertebrae 5 Abdominal region Bears most of the body weight, supports spinal movement and protects nerves

4. Sacral vertebrae 5 Hip region Connects the spine to the pelvis, provides stability and support, and helps to widen the pelvis during delivery

5. Coccyx vertebrae 4 Bottom of the spine Supports sitting and childbirth, serves as an attachment point for muscles, tendons and ligaments

Figure 4.7: Vertebral column of humans Ribs and Sternum (Breastbone): Ribs are curved bones attached at the back to the thoracic vertebrae and at the front (directly or indirectly) to the sternum.

The rib cage encloses and protects vital organs like the heart, liver and lungs.

There are typically twelve pairs of ribs in humans. These are

i. True ribs (first seven pairs) connect directly to the sternum via costal cartilage.

ii. False ribs (next three pairs) connect indirectly to the sternum.

iii. Floating ribs (last two pairs) are not attached to the sternum.

Figure 4.8: Human rib cage.

Appendicular skeleton The appendicular skeleton consists of the bones of the limbs and their associated girdles (shoulder and pelvic girdles), which attach the limbs to the axial skeleton. They allow for movement and flexibility Limb girdles ᵢ. Pectoral (shoulder) girdle: Composed of the scapula (shoulder blade) and clavicle (collarbone). It connects the forelimbs (arms) to the axial skeleton.

ii. Pelvic (hip) girdle: Is formed by the fusion of three bones namely, ilium, ischium and pubis. It connects the hindlimbs (legs) to the vertebral column.

Limbs Each limb has three main sections

i. Upper segment e.g., humerus in the arm, femur in the leg.

ii. Lower segment e.g., radius and ulna in the arm, tibia and fibula in the leg

iii. Terminal segment e.g., hands and feet, including wrist/ankle bones, bones of the palms and feet (metacarpals and metatarsals), bones of fingers and toes (phalanges).

General structure of vertebrae Structurally, all vertebrae have the following features in common.

1. Centrum

2. Neural arch

3. Neural spine

4. Neural canal

5. Transverse processes

6. Anterior facets (prezygapophyses)

7. Posterior facets (postzygpophyses) Centrum (Vertebral body): This is solid and cylindrical, in shape, and forms the main body of the vertebra. It bears weight, provides structural support, and serves as the point of articulation with adjacent vertebrae through intervertebral discs. It bears the neural arch and neural spine.

Neural arch: This is an arch which extends from the back of the centrum. Together with the centrum, it encloses the neural (vertebral) canal. The arch forms the roof of the neural canal, which houses spinal nerves and protects the spinal cord from mechanical injury.

Neural spine (Spinous process): This is an outgrowth which projects upward (or backward in upright posture) from the neural arch. It provides a large surface area for the attachment of muscles and ligaments that support the spine and allow movement.

Transverse processes: These are lateral projections which grow from the junction of the neural arch and centrum. They are paired and serve as sites for muscle and ligament attachment. They also articulate with ribs in some vertebrae.

Facets (Articular processes): These are smooth-surfaced projections that extend from the neural arch. They are arranged in anterior (superior) and posterior (inferior) pairs and articulate with adjacent vertebrae. They form synovial joints that permit controlled movement of the spine.

Neural canal/Vertebral foramen: This is a hollowed channel formed by the neural arch and centrum, which runs through all vertebrae. It houses and protects the spinal cord.

Figure 4.9: General features of a human vertebra Cervical vertebrae (Neck region) These are vertebrae located in the neck region. They are seven bones that form the neck, support the skull and enable head movement. The first two cervical vertebrae, the atlas (C1) and axis (C2) are unique in structure and specialised to perform their functions.

Atlas (C1): Is the first cervical vertebra, located just beneath the skull. It lacks centrum and has a ring-like structure with large articular facets that articulate with each of the two rounded knobs at the base of the skull. It allows up and down nodding movements of the head, as in “yes.”

Figure 4.10: Diagram of atlas.

Image source: https://www.shutterstock.com/image-vector/atlas-c1-vertebra-anatomy- diagram-600nw-2506119559.jpg Axis (C2): Is the second cervical vertebra. It has a peg-like projection called the odontoid process (or dens), which projects upward into the ring of the atlas. This forms a pivot or fulcrum, allowing rotational movement of the head from side to side, as in nodding “no.” The odontoid process fits into a groove on the ventral side of the atlas, stabilised by ligaments to allow safe rotation.

Figure 4.11: Diagram of axis.

Distinguishing Features of Cervical Vertebrae

Cervical vertebrae have features that distinguish them from other vertebrae. These features are:

1. They have a vertebroarterial canal, also called transverse foramen, on each side of the transverse process. This canal allows passage of the vertebral arteries and veins, which supply blood to the brain.

2. They are generally smaller and lighter than other vertebrae.

3. They allow for a wide range of head and neck movements due to their flexibility and specialised structure.

Functions of Cervical vertebrae ₁. They support the head and allow its movement.

2. They protect the spinal cord, blood vessels, and nerves in the neck region.

3. They provide attachment surfaces for neck muscles that control head posture and movement.

Thoracic vertebrae They are located in the thoracic (chest) region of the vertebral column. In humans, there are twelve (12) thoracic vertebrae. This number may be the same or differ on other mammals.

Each thoracic vertebra articulates with a pair of ribs, contributing to the formation of the ribcage. They are more robust than cervical vertebrae due to their role in bearing more weight and providing attachment for ribs and muscles.

Features which distinguish thoracic vertebrae from other vertebrae are:

a. Long neural spine: Their neural (spinous) process is long and points downward and backward, providing a large surface area for the attachment of thoracic muscles and ligaments.

b. Facets for articulation with ribs: Each thoracic vertebra has two sets of facets, which are:

i. Capitular (costal) facets: Found on the centrum for articulation with the head (capitulum) of the rib.

ii. Tubercular facets: Found on transverse processes for articulation with the tubercle of the rib. These articulations form synovial joints that allow for limited movement of the ribs during breathing.

c. Short transverse processes: These processes are relatively short and stout and bear the tubercular facets for rib attachment.

d. Heart-shaped centrum: Centrum is larger and heart-shaped, increasing in size from T1 to T12, to bear more weight from above.

Figure 4.13: A thoracic vertebra Functions of Thoracic Vertebrae

1. Support and stability: The thoracic vertebrae provide strong support for the upper body, including the head, neck, shoulders, and arms.

2. Protection: By forming the posterior part of the rib cage, the thoracic vertebrae help protect vital organs, such as the lungs, liver and heart.

3. Articulation with ribs: Their structure allows the attachment of ribs, enabling the formation of the thoracic cage necessary for respiration.

4. Muscle attachment: The long neural spines and transverse processes serve as anchoring points for back, shoulder, and thoracic muscles, facilitating posture and upper body movement.

5. Facilitate breathing: The slight mobility at the rib-vertebrae joints allows for expansion and contraction of the rib cage during inhalation and exhalation.

Lumbar Vertebrae

These are located in the lower back or upper abdominal region, between the thoracic vertebrae and the sacrum. There are five (5) lumbar vertebrae in humans, while the number may differ in other mammals.

Features of Lumbar Vertebrae

1. Thick large centrum: With broad facets for muscle attachment and support.

2. Long, flattened transverse processes: Which serve as surfaces for attachment of strong back and abdominal muscles.

3. Extra accessory process: Which also serves as a point for muscle attachment.

Figure 4.14: A lumbar vertebra Functions of Lumbar vertebra

1. The large, thick centrum helps to support the upper half of the body, especially the trunk.

2. The broad facets and transverse processes provide ample surface area for muscle attachment, aiding in posture and movement.

3. Lumbar vertebrae absorb stress and shock from activities like walking, lifting, and twisting.

Sacral Vertebrae

There are five (5) sacral vertebrae in humans. These bones are fused together to form a single triangular bone known as the sacrum.

Figure 4.15: A sacral vertebra Functions of the Sacral vertebra

1. They articulate with the pelvic girdle at the sacroiliac joints, providing a strong, stable connection between the spine and the pelvis.

2. They help to transmit the weight of the upper body to the lower limbs.

3. They form the posterior wall of the pelvic cavity, protecting the pelvic organs.

Caudal vertebrae (Coccyx in humans) In humans, there are four (4) caudal vertebrae, which are fused to form the coccyx or tailbone. In tailed mammals such as dogs, cats and rats, these vertebrae extend to form their tail. The number of vertebrae forming the tail depends on length of the tail.

Figure 4.16: Features of a caudal vertebra Appendicular Skeleton This consists of the bones of the limbs and their associated girdles (shoulder and pelvic girdles). The girdles attach the limbs to the axial skeleton. Components of the appendicular skeleton are as follows:

Limb girdles ₐ. Pectoral (shoulder) girdle: Composed of the scapula (shoulder blade) and clavicle (collarbone). It connects the forelimbs (arms) to the axial skeleton.

b. Pelvic (hip) girdle: Is formed by the fusion of three bones namely, ilium, ischium and pubis. It connects the hindlimbs (legs) to the vertebral column.

Limbs Each limb has three main segments:

a. Upper segment: Humerus in the arm, femur in the leg.

b. Lower segment: Radius and ulna in the arm, tibia and fibula in the leg.

c. Terminal segment: Hands and feet, including wrist/ankle bones, bones of the palms and feet (metacarpals and metatarsals, respectively), bones of fingers and toes (phalanges).

Functions of appendicular skeleton

1. Movement

a. Locomotion: The lower limbs are specialized for stability and movement like walking and running.

b. Object manipulation: The upper limbs are designed for a wide range of motion, enabling humans to grasp, lift, and manipulate objects.

c. Leverage and support: It provides leverage for muscles and supports the limbs, allowing for controlled and efficient movement.

2. Muscle attachment: The bony surfaces within the appendicular skeleton serve as attachment sites for muscles, which are essential for any form of skeletal movement.

3. Limb support: The pectoral (shoulder) and pelvic (hip) girdles are crucial components that connect the upper and lower limbs to the axial skeleton, anchoring them to the body’s trunk.

4. Other skeletal functions

a. Cell, fat and cartilage production: The red bone marrow within the appendicular skeleton produces red blood cells while stem cells in the yellow bone marrow may develop into cartilage, fat, or bone cells.

b. Mineral homeostasis: These bones store and release essential minerals into the bloodstream as needed, helping to maintain the body’s mineral balance.

Pelvic Girdle (Hip Girdle)

The pelvic girdle is made up of two fused halves, joined at the front by the pubic symphysis.

Each half consists of the ilium, ischium and pubis. These bones encircle a large opening called the obturator foramen, through which nerves and blood vessels pass.

Figure 4.17: Pelvic girdle Functions of the pelvic girdle ₁. Supports the weight of the body.

2. Protects internal organs, especially the female reproductive system.

3. Articulates with the sacrum and the head of the femur at the acetabulum to form the hip joint.

Limbs Mammals have two pairs of limbs. These are:

a. Forelimbs (upper limbs in humans)

b. Hindlimbs (lower limbs in humans) The fore and hind limbs are built on a basic pentadactyl plan, which consists of five digits (fingers and toes). They are, therefore, known as pentadactyl limbs.

The forelimb is divided into five major parts as follows ₐ. Humerus: Is a long bone of the upper arm, articulating with the scapula at the shoulder joint and the radius/ulna at the elbow.

b. Radius and Ulna: Are two bones of the forearm. The ulna is usually longer and forms the hinge joint at the elbow. The radius allows for rotation of the forearm (pronation and supination).

c. Carpals: They are eight to nine small bones forming the wrist. They articulate with the radius/ulna above and metacarpals below.

d. Metacarpals: They are five long bones forming the palm of the hand. They articulate with the carpals and the phalanges.

e. Phalanges (digits): Are bones of fingers and toes. The thumb, which is the first digit on the hand, has two phalanges while the other four digits each have three.

Each phalanx may end in a nail or claw, depending on the species.

Figure 4.18: A human forelimb.

Hind limb (Lower limb of humans) Each hind limb is divided into five (5) regions namely

a. Femur: Is a long, single bone in the upper hind limb (thigh). It articulates with the acetabulum of the pelvic girdle to form the ball and socket joint at the hip.

b. Tibia and fibula: This pair of bones makes up the shank of the hind limb. The tibia is longer than the fibula. In most mammals, the lower end of the tibia and fibula are fused together while the upper end of the fibula is free.

c. Tarsals: These are bones of the ankle, numbering nine (9). They are small and irregularly shaped. The longer tarsals fit into the tibia and fibula to form the ankle joint. The tarsals also articulate with the metatarsals of the foot.

d. Metatarsals: There are five of them, which are comparatively longer than the tarsals. They make up the bones of the foot and articulate with the tarsals and the phalanges.

e. Phalanges or digits: These are bones of the toes, numbering five (5) in humans.

Figure 4.19: A human hindlimb.

Activity 4.4 Investigating Functions of the Human Skeleton

Aim: To understand how the various parts of the skeleton work in coordination.

What to do

1. Watch a video by the following link: https://youtu.be/f-FF7Qigd3U

2. Fall into ten groups with three to four learners in each group. Two groups will investigate each of the following parts of the skeleton: Skull, Vertebrae, Ribs and sternum, Upper limbs and lower limbs.

3. After watching the video and with further research, write down the functions of each part of the skeleton named above.

4. Compare your findings with those of your sister group.

Discussion: Compare the functions of your part of the skeleton with those of other parts and establish how the various parts work together to coordinate the activities of the skeleton.

Each group should prepare a map of the coordinated functions and present it for class discussion and critique, after which you arrange them for a gallery walk.

Key question: How effective is the collaboration between the axial skeleton and appendicular skeleton?

Muscle tissue is a special kind of body tissue that helps us move. It allows us to walk, run, lift things, breathe and even pump blood through our hearts.

Muscles work by contracting and relaxing, which creates movement in different parts of the body. Each type of muscle has a unique structure that helps it to do its specific job.

By learning about how muscle tissue is built and how it works, we can better understand how it contributes to movement. It’s important to explore its types, structure, organisation, and mechanism of action. Muscle tissue exists in three main forms: skeletal, cardiac and smooth. Each adapts to different roles in the body’s movement and function.

Note

• Muscle tissue contracts to move bones.

• Joints connect bones and allow movement.

• Nerves send signals to muscles, which pull bones to create movement.

• Structure and function of the movement of muscle tissue Muscles Muscle tissue is a fundamental type of tissue composed of cells that contract to create movement in the body and within organs. It enables both voluntary and involuntary actions like walking, pumping blood, and digesting food.

There are three types of muscles in the human body. These are the Smooth/Visceral, Skeletal, and Cardiac

1. Smooth (Visceral) muscle: A smooth muscle tissue is made up of long, spindle-shaped cells. Each cell has one nucleus. These muscles are found in the walls of the alimentary canal (like the stomach and intestine), the uterus, blood vessels, and the excretory system (like the bladder).

The activities of smooth muscles are controlled by the involuntary nervous system and not by our conscious minds. Smooth muscles do not get tired quickly, so they can keep working for a long time without resting.

2. Cardiac muscle: Cardiac muscle is located only in the walls of the heart. It is capable of contracting and relaxing rhythmically throughout a person’s life without becoming fatigued. Cardiac muscle is described as myogenic, which means that its contractions are initiated by the muscle itself rather than by the nervous system, although the nervous system can influence the rate of contraction.

The fibres of cardiac muscle are striated (striped in appearance) and are connected to each other by cross-links, forming an interconnecting network. Each fibre is uninucleate, meaning it contains a single nucleus.

3. Skeletal Muscles: These are attached to two or more bones and are responsible for providing different types of skeletal movements. They are striated, but unlike cardiac muscle, their bundles of fibres are not interconnected. Each muscle fibre contains many nuclei (multinucleate).

One end of a skeletal muscle (the origin) is attached to an immovable bone, such as the scapula, while the other end (the insertion) is attached to a movable bone, such as the radius. Skeletal muscles are controlled by the nervous system and can be moved voluntarily, so they are known as voluntary muscles. They are able to contract and relax to produce movement, but they become fatigued quickly. The ends of skeletal muscles form tendons, which attach the muscles to bones.

Figure 4.20: Muscle tissues

Activity 4.5 Muscles Match

Aim: To identify the types of muscle and their location in the body What you need

• Play-dough/clay to mould muscle

• Cut out pictures of skeletal, smooth and cardiac muscle

• Worksheet

• Blank outline of the human body diagram

• Colour pencils/Crayons/paper sticker What to do

1. Observe the model or pictures of the three muscles discussed

2. Write down your answers to fill in your muscle table.

a. What does it look like?

b. Where is it found in the body

c. What does it do?

3. Take your blank human body diagram

4. Use the colour pencil/ crayon /stickers to show where each muscle type is found.

a. Red for skeletal muscle (arms, legs, etc.)

b. Blue for smooth muscle (stomach, intestine )

c. Purple for cardiac muscle (hearts)

5. In your group, choose one type of muscle

6. Act it out or create a quick movement to show

a. where it is

b. What it does

c. if it moves on its own or if you control it.

JOINT A joint is a junction between two or more bones. It may be immovable, slightly movable or freely movable.

1. Immovable joint: An immovable joint, also known as synarthrosis, is a joint where bones are connected by dense fibrous connective tissue or cartilage, allowing for little to no movement. Immovable joints provide strength and stability. A typical example of immovable joints are the sutures in the skull.

2. Slightly movable joint (Cartilaginous joint): This type of joint allows for limited movement, which provides both stability and flexibility. Its bones are connected by cartilage. Examples are joints between vertebrae, two pelvic bones and where ribs connect to the breastbone.

3. Movable/Synovial joint: This is a joint that allows for a wide range of motion between bones. Movable joints are formed by bones which are not in direct contact with each other. The bones are held loosely together by ligaments and muscles. The entire joint is enclosed in Synovial membrane, which secrets Synovial fluid to lubricate the movement of one bone with another. This allows for a wide range of motion.

The articular surface of each bone is covered with hyaline cartilage, to act as shock absorber. Movable joints are classified on the basis of the degree of movement allowed.

The various types of movable joints, in the human body, are pivot joint, ball and socket joint, hinge joint and gliding joint.

Figure 4.21: Synovial joint Types of Movable Joint ₁. Ball and socket joints: They allow movement in more than one plane (rotation, flexion, adduction and abduction movements). They are so-called because a ball-shaped end fits into a socket. Examples are the shoulder joint (humerus in the scapula) and the hip joint (femur in the pelvis).

Figure 4.22: Ball-and-socket joint at the shoulder

2. Hinge joint: This joint allows movement in only one plane. Examples are the elbow joint, knee joint and joints in the phalanges. At the elbow, the forearm can be raised towards the shoulder in a hinge-like movement just the working of a door hinge. In a similar hinge-like manner, the knee joint causes the leg to be bent backward.

Figure 4.23: Hinge joint at the elbow

3. Gliding Joint/Plane joint: It allows for small, sliding or gliding movements between the flat or nearly flat surfaces of two bones. These joints are essential for stability and fine movements. They are found in the carpals of the wrist, the tarsals of the ankle, and the facet joints of the spine.

Figure 4.24: Gliding joints at wrist and ankle

4. Pivot joint: This type of synovial joint allows for rotation around a single axis, where a rounded bone rotates within a ring-shaped structure of bone and ligaments. Key examples in the human body include the atlantoaxial joint between the atlas and axis which permits “yes” nodding and “no” nodding, respectively; and the radioulnar joint in the forearm, which permits the hand to twist.

Figure 4.25: Pivot joint in the neck Key question: What is the effect of injury to a joint on the whole body?

Activity 4.6 Build and Demonstrate Types of Joints

Aim: To create simple models of different types of joints and use them to demonstrate how each joint allows specific movements.

What you need

• Rubber bands

• Cardboard

• Straws

• Paper fasteners (split pins)

• Scissors

• Glue or tape

• Markers (optional, for labelling) What to do

1. Form small groups (3–5 learners per group).

2. Build models to represent the following joint types:

a. Hinge joint (e.g., elbow or knee): Use cardboard and paper fasteners to create a model that moves in one direction.

b. Ball-and-socket joint (e.g., shoulder or hip): Use a ball made of paper or rubber and a socket from cardboard or a bottle cap to allow rotation in many directions.

c. Pivot joint (e.g., neck): Use straws or rods fixed in a way that allows rotation around a point.

3. Demonstrate each model to another group in the class, showing the type of movement allowed by that joint.

4. Explain the function of each joint type using your model (e.g., “The hinge joint only allows back-and-forth motion like a door”).

Activity 4.7 Identifying Joints In The Body

What to do: The table below shows parts of the body and their corresponding joint.

Copy and complete the table.

Part of the body Name of the joint found there

1. Between vertebrae

2. Gliding/Planar joint

3. Ball-and-socket joint

4. Between cranial bones

5. Hinge joint

6. In phalanges

7. Between radius and ulna

8. Pivot joint

“Left, right, left, right, swing your arms!!!” You must remember your teacher when he/she was training you for the Independence Day march past a few years ago. What facilitates the movement of the arms? Let us delve into this.

The arms move through the action of two important muscles. These are

1. The Biceps muscle, also called the flexor, is located at the front of the upper arm.

2. Triceps muscles, also known as the extensor, are located at the back of the upper arm.

These two types of muscles work by opposing each other (in an antagonistic manner).

Hence, they are always disagreeing with each other. When the biceps contract (shorten), under nervous stimulation, the triceps relax (lengthen). This pulls the radius upward which bends the arm at the elbow (a movement called flexion).

On the other hand, when the triceps contract, the biceps relax. This pulls the ulna downward through the olecranon process, straightening the arm (a movement called extension).This antagonistic muscle action, by the biceps and triceps, is essential for coordinated limb movement, allowing humans to perform tasks such as lifting, pushing, pulling, and throwing.

It also helps maintain joint stability and prevents sudden or jerky movements.

Figure 4.26: Opposing movements of biceps and triceps

Activity 4.8 Demonstrating Flexion And Extension

Aim: To help understand the opposing actions of one’s biceps and triceps.

What to do

1. Place one hand on the front of your other arm’s upper arm.

2. Bring your hand towards your shoulder.

3. Feel your biceps.

4. Now, place the same hand on the back of the same upper arm

5. Straighten your arm completely.

6. Feel your triceps.

7. Repeat the activity in pairs with each other.

Discussion: Discuss your observations among yourselves and share with the rest of the class.

Key question: What do you think would be the effect on arm movement if biceps and triceps did not oppose each other?

1. Study and compare the three different types of skeletons found in animals. Create a comparison that shows how they are similar and different. Your response should;

• give at least two examples of organisms for each type.

• describe the skeletal material involved.

• give advantages and limitations of each type in terms of movement and protection.

• provide information on how each supports survival in different habitats.

2. Describe how the biceps and triceps muscles work antagonistically to move the arm.

3. Compare and contrast the actions of hinge joints and ball-and-socket joints using real- life movements (e.g., kicking vs. waving).

4. Design and explain a model that shows how antagonistic muscles and hinge joints work together to produce controlled limb movement.