How do neurons carry and pass on messages in the nervous system?
Neurons and synapses: the structure and function of neurons, the electrical impulse, and synaptic transmission using neurotransmitters.
A focused answer to Edexcel GCSE Psychology Topic 4, covering the structure and function of neurons, the electrical impulse, and synaptic transmission using neurotransmitters.
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What this dot point is asking
Edexcel wants you to describe the structure and function of neurons and explain how a message travels: as an electrical impulse within a neuron and as a chemical signal across the synapse using neurotransmitters. This biological detail supports treatments (such as how antidepressants change serotonin at the synapse), so learn the sequence precisely.
The structure and function of a neuron
The main parts are:
- Cell body: contains the nucleus, which keeps the cell alive and controls its activities.
- Dendrites: short, branching fibres that receive signals from other neurons and carry them towards the cell body.
- Axon: a long fibre that carries the electrical impulse away from the cell body towards the axon terminals.
- Myelin sheath: a fatty layer covering many axons that insulates them and speeds up the impulse.
- Axon terminals: the endings that release chemicals to the next neuron.
Different neurons do different jobs: sensory neurons carry information from the senses to the brain, motor neurons carry instructions to muscles, and relay neurons connect neurons within the brain and spinal cord.
The electrical impulse and synaptic transmission
This is why the synapse matters for behaviour and treatment. Many drugs work by changing what happens at the synapse, for example SSRIs for depression block the reuptake of serotonin, leaving more in the synapse to act on the next neuron.
Try this
Q1. What is the gap between two neurons called? [1 mark]
- Cue. The synapse (synaptic cleft).
Q2. What is the function of the myelin sheath? [1 mark]
- Cue. It insulates the axon and speeds up the electrical impulse.
Q3. Explain how neurotransmitters carry a message across the synapse. [2 marks]
- Cue. They are released into the gap, diffuse across, and bind to receptors on the next neuron, which can trigger a new impulse.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20193 marksDescribe the structure of a neuron. (Paper 1)Show worked answer →
A 3-mark Describe item rewards the main parts of a neuron and what each does.
A neuron has a cell body containing the nucleus, which keeps the cell alive. Branching dendrites receive signals from other neurons and carry them towards the cell body. A long fibre called the axon carries the electrical impulse away from the cell body towards the axon terminals. The axon is often covered by a fatty myelin sheath, which insulates it and speeds up the impulse.
Markers reward the cell body (with nucleus), dendrites (receiving signals), the axon (carrying the impulse away), and ideally the myelin sheath (insulating and speeding the impulse).
Edexcel 20224 marksExplain how a message is passed from one neuron to another across a synapse. (Paper 1)Show worked answer →
A 4-mark Explain item rewards a clear, ordered account of synaptic transmission.
When an electrical impulse reaches the end of a neuron (the axon terminal), it triggers the release of chemicals called neurotransmitters into the gap between the two neurons, called the synapse (synaptic cleft). The neurotransmitters diffuse across the gap and bind to receptors on the next neuron. This can excite the next neuron, making it more likely to fire its own electrical impulse, so the message continues. Any leftover neurotransmitter is reabsorbed or broken down.
Markers reward the impulse reaching the axon terminal, the release of neurotransmitters into the synapse, their diffusion and binding to receptors on the next neuron, and the triggering of a new impulse.
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Sources & how we know this
- Pearson Edexcel GCSE (9-1) Psychology (1PS0) specification — Pearson Edexcel (2017)