Order the four events at a chemical synapse
Link arriving impulse release diffusion binding and the next impulse.
Section 14.1 · Coordination and response
Extended only (Supplement); Biology 0610, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked
Before you begin
- Recall cell membranes, diffusion, sensitivity and the difference between cells, tissues and organs.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What stimulates transmitter release in this account?
What you will learn
- Start with the arriving electrical impulse
- Finish with stimulation in the next cell
Order the four events at a chemical synapse
Four required events: arriving impulse stimulates release; transmitter diffuses; it binds next-cell receptors; an impulse is stimulated in the next neurone. Original teaching model.
| Feature | Meaning |
|---|---|
| 1 | Impulse stimulates release from vesicles into gap |
| 2 | Neurotransmitters diffuse across gap |
| 3 | Bind receptor proteins on the next neurone |
| 4 | Impulse stimulated in next neurone |
Start with the arriving electrical impulse
The first event in the supplied chemical-synapse account begins when an electrical impulse reaches the presynaptic terminal. It stimulates release of neurotransmitter molecules from vesicles into the synaptic gap. The vesicle membrane and its chemical contents have different roles: the contents are released into the space rather than an intact vesicle travelling all the way through the next neurone.
Second, neurotransmitter molecules diffuse across the synaptic gap. The route crosses the small space between separate cells, rather than blood carrying the transmitter around the body. Third, the neurotransmitter molecules bind to receptor proteins on the next neurone. Diffusion to the receiving side and binding to a receptor are related but distinct steps, so include both in an ordered explanation.
Finish with stimulation in the next cell
Fourth, an electrical impulse is stimulated in the next neurone in the required excitatory model. The output returns to electrical signalling along that cell. The complete chain is electrical arrival, chemical release, chemical diffusion, receptor binding and electrical stimulation of the next cell, with release grouped with the initial arriving-impulse event in the four numbered syllabus events.
Do not omit binding and claim that merely entering the space always completes transmission. The explanation also does not say that an electrical impulse jumps directly across the gap. The supplied model describes stimulation of the next neurone; wider biology includes other synaptic effects, but those do not replace the specified four-event sequence required here.
Pause and explain
What immediately follows transmitter diffusion in the required sequence?
Worked example
Order the four specified synaptic events.
Show the worked solution
- Arrival stimulates release, then transmitter diffuses across the gap.
- It binds to next-cell receptor proteins, then an impulse is stimulated there.
Answer Impulse stimulates transmitter release from vesicles into gap → diffusion across gap → binding to receptor proteins on next neurone → impulse stimulated in next neurone.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Give all four required events in their order.
Give me a hint
Keep diffusion and receptor binding as separate events.
Compare my reasoning
- Impulse stimulates release from vesicles into gap, then molecules diffuse across.
- They bind receptor proteins on the next neurone, then stimulate an impulse there.
Impulse stimulates neurotransmitter release from vesicles into the gap; neurotransmitters diffuse across; bind receptor proteins on the next neurone; an impulse is stimulated in that neurone.
Look for these in your work
- Include all four
- Keep the correct order
A student gives release, next impulse, diffusion, binding. Repair the order.
Give me a hint
The chemical signal must reach and bind the receiving side first.
Compare my reasoning
- Keep release before diffusion.
- Put binding after diffusion and next impulse after binding.
Release → diffusion across gap → receptor binding → stimulation of the next impulse, with the arriving impulse triggering release.
Look for these in your work
- Repair both misplaced stages
- Include the arriving trigger
Evaluate: an electrical impulse crosses the gap and no receptor proteins are involved.
Give me a hint
Distinguish within-cell and between-cell signalling.
Compare my reasoning
- The gap is crossed by neurotransmitter molecules in this chemical model.
- Binding to receptor proteins precedes next-cell impulse stimulation.
Incorrect. Neurotransmitter molecules diffuse across the gap and bind receptor proteins; this stimulates an electrical impulse in the next neurone in the supplied model.
Look for these in your work
- State chemical gap transmission
- Retain binding and next impulse
Common mistakes
- Omitting receptor binding.
- Sending an intact vesicle along the next neurone.
What can you explain now?
What immediately follows transmitter diffusion in the required sequence?
Compare with the explanation
Binding to receptor proteins on the next neurone
Binding connects chemical arrival with next-cell stimulation.
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Make it stick
Explain the four synaptic events in order without omitting diffusion or binding.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.