CB2.3 — The nervous system (Edexcel 1SC0)
The nervous system coordinates rapid responses to stimuli via electrical impulses.
Structure
- Central nervous system (CNS): brain + spinal cord — processes information.
- Peripheral nervous system: sensory and motor neurones connecting CNS to body.
Types of neurone
| Neurone | Function | Direction |
|---|---|---|
| Sensory | Carries impulse from receptor to CNS | → CNS |
| Relay | Connects sensory to motor in CNS | Within CNS |
| Motor | Carries impulse from CNS to effector | CNS → |
Synapses
A synapse is a gap between neurones. Signal crosses chemically:
- Electrical impulse arrives at presynaptic neurone.
- Vesicles release neurotransmitter into the synapse.
- Neurotransmitter diffuses across the gap.
- Binds to receptor on postsynaptic membrane → new electrical impulse.
Reflex arc
Stimulus → receptor → sensory neurone → relay neurone (spinal cord) → motor neurone → effector (muscle/gland) → response.
Reflexes are fast, automatic and involuntary — they protect the body without waiting for the brain.
Example: hand touching a hot surface → withdrawing hand before pain is consciously felt.
AI-generated · claude-opus-4-7 · v3-edexcel-combined-science