# The Nervous System
The nervous system allows organisms to detect and respond to changes in their environment. It coordinates rapid, short-lived responses.
1. Structure of the Nervous System
- CNS: brain + spinal cord (coordination centre)
- Peripheral nervous system: sensory and motor neurones
Pathway: stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response
2. Types of Neurones
| Type | Function | Direction |
|---|---|---|
| Sensory | Carries impulses from receptors to CNS | Receptor → CNS |
| Relay | Connects sensory to motor in CNS | Within CNS |
| Motor | Carries impulses from CNS to effectors | CNS → Effector |
Synapse: gap between two neurones. Signal crosses by chemical diffusion (neurotransmitters).
3. Reflex Arc
Automatic, rapid response to protect the body.
Path: receptor → sensory neurone → relay neurone (in spinal cord) → motor neurone → effector (muscle contracts)
Example: touching a hot object → hand pulls away before you consciously feel pain.
Advantages: fast (doesn't involve brain for decision), protective.
4. The Brain (Higher Tier)
| Region | Function |
|---|---|
| Cerebral cortex | Consciousness, memory, language, intelligence |
| Cerebellum | Balance, coordination of movement |
| Medulla oblongata | Unconscious activities (heart rate, breathing) |
Studied using: MRI, CT scans, electrical stimulation, studying brain-damaged patients.
5. The Eye
| Part | Function |
|---|---|
| Cornea | Refracts light |
| Iris | Controls pupil size (amount of light entering) |
| Lens | Focuses light on retina (accommodation) |
| Retina | Contains receptors (rods and cones) |
| Optic nerve | Carries impulses to brain |
Accommodation: changing lens shape to focus on near/far objects.
- Near: ciliary muscles contract → suspensory ligaments slack → lens becomes fat
- Far: ciliary muscles relax → suspensory ligaments taut → lens becomes thin
6. Practice Questions
- Describe the pathway of a reflex arc.
- What is the function of a synapse?
- Compare sensory and motor neurones.
- Explain how the eye focuses on a near object.
- Name the three main regions of the brain and their functions.
Want to check your answers and get step-by-step solutions?
Summary
- Stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response
- Reflex arcs: fast, automatic, protective
- Synapses: chemical transmission across gaps
- Brain: cerebral cortex (consciousness), cerebellum (coordination), medulla (unconscious)
- Eye: accommodation changes lens shape for focusing