The Nervous System – JSS3 Intermediate Science Lesson Note (Second Term)

The nervous system is the network of the brain, spinal cord and nerves that senses changes, processes information and controls how the body responds.

Behavioural objectives

1. Define the nervous system and state its three main functions.
2. Name the parts of the central and peripheral nervous systems.
3. State the functions of the cerebrum, cerebellum and medulla oblongata.
4. Distinguish between sensory nerves and motor nerves.
5. Describe the path of a reflex action.
6. List ways of keeping the nervous system healthy.

What does the nervous system do?

The nervous system has three main jobs: sensing, processing and responding.

• Sensing: it gathers information from inside and outside the body, such as the feel of a mosquito bite.
• Processing: it decides what the information means, such as recognising that the bite is itchy or painful.
• Responding: it tells the body what to do, such as telling the hand to scratch the spot.

What are the main parts of the nervous system?

The nervous system has two main divisions: the central nervous system and the peripheral nervous system.

• Central nervous system (CNS): the headquarters, made up of the brain and the spinal cord.
• Peripheral nervous system (PNS): the messengers, made up of the nerves that spread from the brain and spinal cord to the whole body.

What is the brain and what are its parts?

The brain is the control centre of the body, protected inside the skull.

• Cerebrum: the largest part, which handles thinking, memory, voluntary movement and understanding what the senses detect.
• Cerebellum: sits at the back of the brain and controls balance and coordination, such as riding a bicycle without falling.
• Medulla oblongata: part of the brain stem, which controls actions you do not think about, such as heartbeat and breathing.

What is the spinal cord?

The spinal cord is a long bundle of nerve tissue that runs down the back and links the brain to the rest of the body.

• Protection: the backbone (vertebrae) surrounds and protects it.
• Link: it carries messages between the brain and the nerves of the body.
• Reflex centre: some messages turn back at the spinal cord and go straight to the muscles.

What are nerves?

Nerves are thin, wire-like bundles of nerve fibres that spread from the brain and spinal cord to every part of the body, even the toes.

Sensory nerves

• Direction: carry messages from the sense organs to the brain and spinal cord.
• Example: “This pepper is hot!”

Motor nerves

• Direction: carry messages from the brain and spinal cord to muscles and glands.
• Example: “Move your tongue and drink water!”

What is a neuron?

A neuron is a nerve cell that carries messages as tiny electrical signals called nerve impulses.

• Cell body: contains the nucleus and controls the cell.
• Dendrites: short, branched arms that catch signals.
• Axon: a long tail that sends signals away from the cell body.
• Shape: neurons are long and branched, unlike regular round cells.
• Nerves: each nerve is made of bundles of neuron fibres, and the brain holds billions of neurons.

What are the types of neurons?

There are three types of neuron: sensory, motor and relay.

• Sensory neuron: carries impulses from a receptor to the CNS.
• Relay neuron: passes impulses inside the CNS, for example in the spinal cord.
• Motor neuron: carries impulses from the CNS to a muscle or gland.

What is a reflex action?

A reflex action is a quick, automatic response to a stimulus that does not wait for a decision from the brain.

• Example: pulling your hand away from a hot stove before you feel the pain.
• Example: jumping when you hear a loud bang.
• Purpose: it protects the body from harm in the shortest time.

What is the path of a reflex action?

1. A stimulus, such as heat, acts on the body.
2. A receptor in the skin detects it.
3. A sensory neuron carries the impulse to the spinal cord.
4. A relay neuron in the spinal cord passes the impulse on.
5. A motor neuron carries the impulse to a muscle.
6. The muscle (effector) contracts and the hand moves away.

How does a reflex action differ from a voluntary action?

A voluntary action is one you decide to do, such as writing, and it is controlled by the cerebrum.

How can we keep the nervous system healthy?

We keep the nervous system healthy by protecting the head and spine and by living healthily.

1. Wear a helmet: protect your skull when riding a bicycle or motorcycle, because a brain injury is very serious.
2. Get enough sleep: the brain rests and recovers while you sleep.
3. Eat good food: fish, eggs and green vegetables support the brain.
4. Avoid drugs and alcohol: they disturb the nerves and can permanently damage brain cells.

Evaluation

1. Name the three main parts of the brain and state one function of each.
2. State two differences between a sensory nerve and a motor nerve.
3. What protects the spinal cord from injury?
4. Define a reflex action and give one example.
5. Name the three parts of a neuron and state what each does.

Assignment

Draw and label a neuron. Then write the six steps of a reflex action, using the example of touching a hot pot.