GCSE Biology · Edexcel 1BI0 · Topic 2C
The nervous system
Key points
- The nervous system is the brain and spinal cord (central nervous system) plus nerves. It carries fast electrical impulses.
- Sensory neurones carry impulses from receptors to the CNS; relay neurones are in the CNS; motor neurones carry impulses to effectors (muscles or glands).
- Neurones have a long axon covered in a myelin sheath, which insulates it and speeds up the impulse; dendrites connect to other neurones.
- A synapse is a tiny gap between neurones. The impulse causes a neurotransmitter to be released, which diffuses across the gap and starts an impulse in the next neurone.
- A reflex arc: stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response. It is fast and automatic because it bypasses the conscious brain, protecting the body from harm.
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The nervous system lets animals detect changes and respond in fractions of a second. This sub-topic covers the structure of neurones, how signals cross synapses, and how a reflex arc protects you before you are even aware of danger.
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