The Process of Synaptic Transmission (AQA AS Psychology)

Revision Note

Claire Neeson

Written by: Claire Neeson

Reviewed by: Lucy Vinson

The process of synaptic transmission

  • The junction where two neurons meet is known as a synapse

  • A synapse consists of:

    • the presynaptic knob:

      • A swelling at the end of the presynaptic neuron; it contains vesicles which hold neurotransmitters

    • the synaptic cleft:

      • The space in between the axon of one neuron and the dendrites of another; where the electrical signal is turned into a chemical messenger that can be detected by the next neuron

    • the postsynaptic membrane

      • The membrane receives a signal (and binds the neurotransmitter) from the presynaptic neuron

Diagram of a synapse showing a presynaptic membrane with vesicles containing neurotransmitters, synaptic cleft, postsynaptic membrane, and neurotransmitter receptor molecules.
The structure of a synapse and associated neurones.

What happens at a synapse?

  • Synaptic transmission involves a series of events

    1. A signal begins as an electrical impulse (an action potential) within the presynaptic neuron

    2. When the electrical impulse arrives at the end of the axon on the pre-synaptic knob, chemical messengers called neurotransmitters are released from structures called vesicles at the presynaptic membrane

    3. Neurotransmitters are released into the synaptic cleft as a chemical substance from the presynaptic neuron after the action potential has occurred

    4. Neurotransmitters diffuse across the synaptic cleft and temporarily bind with receptor sites on the postsynaptic membrane

    5. This action stimulates the postsynaptic neuron to generate another electrical impulse (action potential) that then travels down the axon of the postsynaptic neuron

    6. The neurotransmitter molecules are then destroyed by enzymes or recycled to prevent continued stimulation of the second neuron, which could cause repeated impulses to be sent

    7. The re-absorbed neurotransmitter may be used again by the presynaptic neuron

Illustration of neuron communication showing an impulse arriving at the presynaptic neuron, neurotransmitter release, synaptic cleft diffusion, receptor binding, impulse triggering, and neurotransmitter recycling.
Synaptic transmission

Neurotransmitters

  • Neurotransmitters are many and varied, each having a specific function with accompanying receptor sites ready to 'catch it' e.g.

    • Serotonin receptor 4 (5-HT4R) plays an important role in regulating mood, particularly depression and anxiety

    • Dopamine receptors play an essential role in movement and the experience and anticipation of reward

      • dopamine receptors are located in the hippocampal dentate gyrus

  • Neurotransmitters are either excitatory or inhibitory

Excitatory neurotransmitters

  • Excitatory neurotransmitters are those which stimulate an action potential in the postsynaptic neuron

  • Excitatory neurotransmitters increase the neuron’s positive charge

    • Increasing the neuron's positive charge makes it more likely to ‘fire’

  • Adrenaline is an excitatory neurotransmitter

Inhibitory neurotransmitters

  • Inhibitory neurotransmitters are those which inhibit an action potential in the postsynaptic neuron

  • Inhibitory neurotransmitters increase the neuron’s negative charge

    • Increasing the neuron's negative charge makes it less likely to ‘fire’

  • Serotonin is an inhibitory neurotransmitter

Examiner Tips and Tricks

Make sure that you know each stage of what is involved in synaptic transmission. For example, you may be asked to:

'Outline the structures and processes involved in synaptic transmission'

[6 marks]

To achieve a mark in the top band for this question you would be expected to:

  • Communicate secure and confident knowledge of both the structures and the processes involved in synaptic transmission

  • You would need to include references to both presynaptic and postsynaptic processes

  • Your answer would need to be accurate and with a good level of detail

  • Your answer would have to be clear and coherent

  • You would be expected to use specialist terminology effectively

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Claire Neeson

Author: Claire Neeson

Expertise: Psychology Content Creator

Claire has been teaching for 34 years, in the UK and overseas. She has taught GCSE, A-level and IB Psychology which has been a lot of fun and extremely exhausting! Claire is now a freelance Psychology teacher and content creator, producing textbooks, revision notes and (hopefully) exciting and interactive teaching materials for use in the classroom and for exam prep. Her passion (apart from Psychology of course) is roller skating and when she is not working (or watching 'Coronation Street') she can be found busting some impressive moves on her local roller rink.

Lucy Vinson

Author: Lucy Vinson

Expertise: Psychology Subject Lead

Lucy has been a part of Save My Exams since 2024 and is responsible for all things Psychology & Social Science in her role as Subject Lead. Prior to this, Lucy taught for 5 years, including Computing (KS3), Geography (KS3 & GCSE) and Psychology A Level as a Subject Lead for 4 years. She loves teaching research methods and psychopathology. Outside of the classroom, she has provided pastoral support for hundreds of boarding students over a four year period as a boarding house tutor.