Quick Summary
The nervous system controls and coordinates body activities. Focus on neuron structure, central nervous system, peripheral nerves, reflex action, and sense organs.
Key Definitions
- Neuron: Structural and functional unit of the nervous system.
- Stimulus: Change in the environment that produces a response.
- Impulse: Electrical signal carried by neurons.
- Central nervous system: Brain and spinal cord.
- Peripheral nervous system: Nerves outside the brain and spinal cord.
- Reflex action: Quick automatic response to a stimulus.
- Reflex arc: Pathway followed by nerve impulses during reflex action.
Structure of a Neuron
| Part | Function |
|---|---|
| Dendrite | Receives impulses |
| Cell body | Contains nucleus and cytoplasm |
| Axon | Carries impulses away from cell body |
| Nerve ending | Passes impulse to another cell |
Brain
| Part | Function |
|---|---|
| Cerebrum | Thinking, memory, intelligence, voluntary actions |
| Cerebellum | Balance and coordination |
| Medulla oblongata | Involuntary actions such as breathing and heartbeat |
How a Nerve Impulse Travels (synapse)
An impulse travels along the axon as an electrical signal. At the synapse (gap between two neurons), the electrical signal triggers release of a neurotransmitter chemical that crosses the gap and starts a new impulse in the next neuron. Transmission is therefore electrochemical and one-way.
Reflex Action
Reflex action protects the body from harm. For example, withdrawing the hand from a hot object happens quickly through a reflex arc — the impulse takes a shortcut through the spinal cord without waiting for the brain, which is why it is so fast.
The Reflex Arc — sequence
Central vs Peripheral Nervous System
Sense Organs
Sense organs receive stimuli from the environment. Eyes, ears, nose, tongue, and skin help in vision, hearing, smell, taste, and touch.
Textbook Solution Strategy
1. For neuron questions, draw and label dendrite, cell body, axon, and nerve ending. 2. For brain questions, write part plus function. 3. For reflex action, explain stimulus, sensory neuron, spinal cord, motor neuron, and response. 4. Use examples for coordination answers. 5. Keep definitions short and exact.
Important Questions
One Mark
- Define neuron.
- What is reflex action?
- Name the largest part of the brain.
Two Marks
- Differentiate between voluntary and involuntary actions.
- Write the functions of cerebrum and cerebellum.
- What is a reflex arc?
Five Marks
- Explain the structure of a neuron with diagram.
- Describe reflex action with an example.
- Explain the main parts of the brain and their functions.
Common Mistakes
- Confusing cerebrum and cerebellum functions.
- Writing reflex action as a slow conscious response.
- Drawing neuron without labels.
- Forgetting the spinal cord role in reflex action.
Revision Checklist
- Neuron diagram practised
- Brain parts and functions memorised
- Reflex arc sequence revised
- CNS and PNS meanings understood
- Sense organ functions revised