Neurones and synapses

Your nervous system carries electrical impulses along neurones. Each type of neurone has a shape that suits its job, and synapses link them together.

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Parts of a neurone

Cell body: contains the nucleus.
Dendrites: short branches that receive impulses from other neurones.
Dendron: a long fibre that carries impulses towards the cell body (in sensory neurones).
Axon: a long fibre that carries impulses away from the cell body.
Myelin sheath: a fatty layer around many axons and dendrons. It insulates them and makes impulses travel faster.

Three types of neurone

NeuroneJobShape
SensoryCarries impulses from a receptor to the CNSLong dendron, cell body part-way along, short axon
RelayPasses impulses between neurones inside the CNSShort, with many connections
MotorCarries impulses from the CNS to an effector (muscle or gland)Cell body in the CNS, many dendrites, long axon

Receptors and synapses

Receptors detect a stimulus and start an impulse: for example light receptors in the eye and temperature receptors in the skin.
At a synapse: 1. an impulse reaches the end of the axon; 2. a neurotransmitter is released; 3. it diffuses across the gap; 4. it binds to receptors on the next neurone and starts a new impulse.
Neurotransmitter is only released on one side, so impulses cross a synapse in one direction.
Worked example

Put these synapse events in order: A neurotransmitter diffuses across the gap. B An impulse reaches the end of the axon. C A new impulse starts in the next neurone. D Neurotransmitter is released.

  1. The impulse must arrive first (B).
  2. It causes release of neurotransmitter (D).
  3. The neurotransmitter diffuses across (A) and starts a new impulse (C).

Answer: B, D, A, C

Key idea

Dendrites receive impulses, the dendron carries them towards the cell body and the axon carries them away. The myelin sheath insulates and speeds up impulses. At a synapse a neurotransmitter diffuses across the gap.

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Extra practice

2 more questions

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  1. What is the job of the axon?

    1. To detect stimuli
    2. To receive impulses
    3. To release hormones
    4. To carry impulses away from the cell body
    Show the answer

    Answer: To carry impulses away from the cell body

    Axons are long fibres.

  2. Which neurone carries impulses from a receptor to the CNS?

    1. Sensory neurone
    2. Relay neurone
    3. Motor neurone
    4. Effector
    Show the answer

    Answer: Sensory neurone

    Sensory neurones bring information in.

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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