Explain how sensory receptor cells detect stimuli
Link receptor stimulation to a change in receptor-cell activity and impulse transmission in an associated 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
What does a sensory receptor cell do first when stimulated?
What you will learn
- Outline the role of sensory receptor cells in detecting stimuli
- Explain how receptor-cell activity stimulates impulse transmission in sensory neurones
Build the mechanism
A sensory receptor cell detects a particular type of stimulus. Stimulation changes its membrane potential and can cause release of neurotransmitter onto an associated sensory neurone. If the sensory neurone reaches threshold, it generates action potentials that carry information towards the CNS. The receptor cell transduces a stimulus into a signal that can enter the nervous pathway.
Keep the sequence precise
A receptor-cell response is not itself necessarily an action potential in the sensory neurone. Keep the cell membrane changes, synaptic transmission and sensory-neurone impulse as distinct steps.
Pause and explain
Explain why different receptor cells can detect different kinds of stimuli.
Worked example
A receptor stimulus increases transmitter release onto a sensory neurone. Explain the next step.
Show the worked solution
- Transmitter changes the sensory-neurone membrane potential.
- If threshold is reached, action potentials are generated.
Answer The neurotransmitter changes the sensory-neurone membrane potential. If depolarisation reaches threshold, action potentials travel along the sensory 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.
Describe how receptor stimulation can lead to impulses in a sensory neurone.
Give me a hint
Name the first event, then follow each link in order.
Compare my reasoning
- The receptor cell changes its activity after detecting the stimulus.
- Transmitter affects the sensory neurone, which fires if threshold is reached.
A stimulus changes the receptor-cell membrane potential and can trigger neurotransmitter release. The sensory neurone is stimulated and generates action potentials if its threshold is reached.
Look for these in your work
- Mechanism stated
- Steps linked in order
A receptor detects a stimulus but the sensory neurone remains below threshold. What can you conclude?
Give me a hint
Use the terms in the question and state what changes.
Compare my reasoning
- Detection occurred at the receptor.
- Action potentials require sufficient depolarisation of the sensory neurone.
The receptor detected the stimulus, but it did not produce enough postsynaptic depolarisation to reach the sensory neurone threshold, so an action potential was not generated.
Look for these in your work
- Evidence interpreted
- Biological direction explained
Explain why different receptor cells can detect different kinds of stimuli.
Give me a hint
Apply the mechanism to the new context without adding unsupported claims.
Compare my reasoning
- Receptors have specialised stimulus-sensitive proteins or structures.
- This changes cell activity in response to particular conditions.
Different receptor cells have specialised structures or molecules responsive to particular stimuli. Their activity changes when the relevant stimulus is detected, initiating an appropriate sensory pathway.
Look for these in your work
- Mechanism applied
- Limits preserved
Common mistakes
- Skipping the receptor-cell response
- Claiming a stimulus always produces an impulse regardless of threshold
What can you explain now?
What does a sensory receptor cell do first when stimulated?
Compare with the explanation
Its activity or membrane potential changes
The receptor response can then stimulate transmission in an associated sensory neurone.
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Make it stick
How does a receptor-cell response connect a stimulus to a sensory-neurone impulse?
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