Trace taste-bud stimulation to an action potential
Describe how a chemoreceptor cell in a human taste bud stimulates an action potential in a sensory neurone.
A Level; Cambridge International Biology 9700, 2028–2030. Written answers are self-checked; this is not practical-skills certification.
Before you begin
- A control pathway links a stimulus, receptor, coordination system and response.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Where is the action potential generated in this taste pathway?
What you will learn
- Use a taste-bud chemoreceptor as an example of sensory transduction
- Sequence receptor-cell depolarisation, neurotransmitter release and sensory-neurone action potential
Taste receptor cell to sensory impulse
| Feature | Meaning |
|---|---|
| Stimulus | Taste chemical binds to a receptor on a chemoreceptor cell |
| Receptor response | Receptor-cell membrane potential changes |
| Synaptic step | Neurotransmitter is released towards the sensory neurone |
| Output | The sensory neurone generates action potentials |
Build the mechanism
A dissolved taste chemical binds to a receptor on a chemoreceptor cell in a taste bud. The receptor-cell membrane potential changes; depolarisation promotes neurotransmitter release onto the associated sensory neurone. If the sensory neurone reaches threshold, voltage-gated channels open and action potentials propagate towards the CNS. The action potential is in the sensory neurone, after the receptor-cell and synaptic steps.
Keep the sequence precise
Do not say the taste chemical itself travels along the sensory neurone. It stimulates the receptor cell; chemical synaptic transmission then excites the neurone.
Pause and explain
A learner says taste chemicals are carried down the sensory axon. Correct the sequence.
Worked example
Put these events in order: sensory-neurone action potential, taste chemical binds, transmitter release, receptor-cell depolarisation.
Show the worked solution
- Binding changes receptor-cell activity.
- Depolarisation leads to transmitter release, then the neurone reaches threshold.
Answer Taste chemical binds → receptor cell depolarises → neurotransmitter is released → sensory neurone reaches threshold and generates an action potential.
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Test this topic →From guided practice to a new situation
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.
Explain how a dissolved taste molecule can lead to an impulse towards the CNS.
Give me a hint
Name the first event, then follow each link in order.
Compare my reasoning
- Binding changes a chemoreceptor cell.
- Transmitter excites a sensory neurone to threshold.
The taste molecule binds to a chemoreceptor on a taste-bud cell. The cell depolarises and releases neurotransmitter; the associated sensory neurone reaches threshold and propagates an action potential towards the CNS.
Look for these in your work
- Mechanism stated
- Steps linked in order
A diagram shows transmitter released from a taste cell, but no impulse in the sensory neurone. Give one reason this can occur.
Give me a hint
Use the terms in the question and state what changes.
Compare my reasoning
- Transmitter release does not guarantee threshold.
- The postsynaptic response may be too small.
The sensory neurone may not reach threshold. The amount of transmitter or the neurone’s current state may produce insufficient depolarisation.
Look for these in your work
- Evidence interpreted
- Biological direction explained
A learner says taste chemicals are carried down the sensory axon. Correct the sequence.
Give me a hint
Apply the mechanism to the new context without adding unsupported claims.
Compare my reasoning
- Taste chemicals bind at the receptor cell.
- Electrical impulses travel along the sensory axon only after synaptic stimulation.
Taste chemicals bind to receptor molecules on a taste-bud chemoreceptor cell. That cell releases neurotransmitter onto a sensory neurone, whose action potentials travel along the axon.
Look for these in your work
- Mechanism applied
- Limits preserved
Common mistakes
- Placing the action potential in the taste chemical
- Omitting neurotransmitter at the receptor-to-neurone connection
What can you explain now?
Where is the action potential generated in this taste pathway?
Compare with the explanation
In the associated sensory neurone
The chemoreceptor cell first changes its activity and releases transmitter.
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Make it stick
What events separate taste-chemical binding from the sensory-neurone impulse?
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.