How do neurons carry and pass on messages in the body?
Neurons and synaptic transmission: the structure of sensory, relay and motor neurons, the electrical impulse, and how neurotransmitters cross the synapse.
A focused answer to AQA GCSE Psychology 3.7, covering neurons and synaptic transmission, including the structure and function of sensory, relay and motor neurons, the electrical impulse along a neuron, and how neurotransmitters cross the synapse.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
AQA wants you to describe the structure and function of the three types of neuron (sensory, relay and motor), explain how an electrical impulse travels along a neuron, and explain how a message crosses the synapse using neurotransmitters. In Paper 2 this is examined with short outline questions and with multi-mark "describe the process" items, so you need the sequence in order.
The structure of a neuron
Many axons are covered in a fatty myelin sheath, which insulates the axon and speeds up the electrical impulse. The three types differ in structure to suit their jobs:
- Sensory neuron: long dendrites and short axons; carries messages from the sense organs to the central nervous system.
- Relay neuron: short dendrites and short axons; found in the CNS, it connects sensory neurons to motor neurons.
- Motor neuron: short dendrites and long axons; carries messages from the CNS to the muscles and glands so the body can respond.
Synaptic transmission
Why this matters
Neurons and synaptic transmission are how the whole nervous system communicates, from detecting a sensation to producing a response. Understanding the synapse also explains how some drugs and treatments work: many antidepressants, for example, change how much neurotransmitter is available in the synapse by blocking reuptake, which is why this topic links to psychological problems.
Try this
Q1. Name the three types of neuron. [3 marks]
- Cue. Sensory, relay and motor neurons.
Q2. Explain how a message crosses the synapse. [3 marks]
- Cue. Neurotransmitters are released into the gap, diffuse across, and bind to receptors on the next neuron, starting a new impulse.
Q3. Identify the part of the neuron that speeds up the electrical impulse. [1 mark]
- Cue. The myelin sheath.
Exam-style practice questions
Practice questions written in the style of AQA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AQA 20204 marksDescribe the process of synaptic transmission. (Paper 2, Section C)Show worked answer →
A 4-mark Describe item rewards a sequenced account, ideally four linked stages.
- An electrical impulse (action potential) travels down the axon of the first neuron and arrives at the axon terminal.
- This triggers the release of chemical messengers called neurotransmitters from vesicles into the synapse (the tiny gap between the two neurons).
- The neurotransmitters diffuse across the synapse and bind to receptor sites on the dendrite of the next neuron.
- This either excites the next neuron (making a new impulse more likely) or inhibits it; any neurotransmitter left in the gap is reabsorbed (reuptake).
Markers reward the correct sequence: electrical impulse, neurotransmitter release, diffusion across the gap, binding to receptors. They penalise saying the electrical impulse itself crosses the synapse.
AQA 20173 marksOutline the function of a sensory neuron, a relay neuron and a motor neuron. (Paper 2, Section C)Show worked answer →
A 3-mark item that rewards one creditworthy point per neuron.
A sensory neuron carries messages from the sense organs (such as the eyes or skin) to the central nervous system. A relay neuron is found within the central nervous system and connects sensory neurons to motor neurons, allowing them to communicate. A motor neuron carries messages from the central nervous system out to effectors (the muscles and glands) so the body can respond.
Markers reward the direction of travel for each (in from senses, connecting inside the CNS, out to muscles or glands). A common error is to swap sensory and motor.
Related dot points
- The structure and function of the nervous system: the central and peripheral nervous systems, the autonomic nervous system, and the fight or flight response.
A focused answer to AQA GCSE Psychology 3.7, covering the structure and function of the nervous system, including the central and peripheral nervous systems, the autonomic nervous system, and the fight or flight response.
- The structure and function of the brain: the four lobes of the cerebral cortex, the cerebellum and the autonomic functions, and the role of the brainstem.
A focused answer to AQA GCSE Psychology 3.7, covering the main structures of the brain, including the four lobes of the cerebral cortex (frontal, parietal, temporal and occipital), the cerebellum and the brainstem, and their functions.
- Localisation of function and ways of studying the brain: language areas, the role of neuropsychology, Penfield's work, and scanning techniques such as CT, PET and fMRI.
A focused answer to AQA GCSE Psychology 3.7, covering localisation of function (including language areas), the role of neuropsychology and Penfield's work, and the brain scanning techniques used to study the brain such as CT, PET and fMRI.
- Encoding and retrieval in memory: acoustic and semantic encoding, the reconstructive nature of memory (Bartlett's War of the Ghosts), and the effect of context and cues on retrieval.
A focused answer to AQA GCSE Psychology 3.1, covering acoustic and semantic encoding, the reconstructive nature of memory shown by Bartlett's War of the Ghosts study, and the effect of context and cues on retrieval.
Sources & how we know this
- AQA GCSE Psychology (8182) specification — AQA (2017)