Trace a supplied withdrawal reflex from stimulus to movement
Explain how the five-part route produces a muscle response.
Section B13.1 · Coordination and response
Mapped to the named 0654 section using teaching from the corresponding single-science course. A 0654-specific review of every Core and Supplement objective is still in progress. Written practice is self-checked; it does not demonstrate supervised laboratory competence or award an official Cambridge grade.
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 carries the outgoing signal towards the muscle?
What you will learn
- Connect the hypothetical input with neural stages
- Separate rapid initiation from later awareness
Trace a supplied withdrawal reflex from stimulus to movement
| Feature | Meaning |
|---|---|
| Input | Skin receptor detects the specified stimulus |
| Central connection | Sensory input → spinal relay |
| Outgoing signal | Motor neurone towards muscle |
| Response | Muscle contraction moves the limb away |
Connect the hypothetical input with neural stages
In the supplied paper model, a potentially damaging skin stimulus activates a receptor. A sensory neurone communicates towards the spinal cord, where a relay neurone connects the incoming information with an outgoing motor pathway. The motor neurone communicates to a muscle effector, and contraction moves the limb away.
Detection, neural communication and movement are different events in the explanation. The receptor does not itself pull the whole limb, and the motor neurone is not the same structure as the muscle. Include receptor, sensory neurone, relay neurone, motor neurone and muscle effector to show how the supplied input is linked with the response.
Separate rapid initiation from later awareness
The specified spinal reflex can be initiated automatically without waiting for a conscious decision to withdraw. Information can also reach the brain, allowing awareness of the event. Automatic initiation therefore does not mean the brain can never receive information, and the spinal example should not become a claim that every reflex is processed only in the spinal cord.
This activity uses a written scenario and labelled diagram rather than asking learners to provoke a painful stimulus. Its aim is to explain the pathway. The simple model does not include every inhibitory connection or muscle pair involved in real withdrawal, so use the supplied arc to describe the required coordinated muscle response without claiming that its drawing is a complete circuit map.
Sources for this lesson
Pause and explain
What produces movement in the supplied reflex?
Worked example
Trace the supplied withdrawal model from receptor to movement.
Show the worked solution
- Sensory communication reaches a central relay.
- Motor communication reaches muscle, whose contraction moves the limb.
Answer Receptor → sensory neurone → spinal relay neurone → motor neurone → muscle effector contracts, moving the limb away.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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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.
Explain the supplied withdrawal pathway including all five parts.
Give me a hint
Link communication with the final tissue action.
Compare my reasoning
- Receptor input travels by sensory neurone to a spinal relay.
- Relay connects with motor neurone, which supplies muscle effector.
Receptor → sensory neurone → relay neurone in spinal cord → motor neurone → muscle effector contracts and moves the limb away.
Look for these in your work
- Include all five parts
- State muscle contraction
Does automatic spinal initiation mean the brain cannot become aware of the event?
Give me a hint
Initiation and awareness are different.
Compare my reasoning
- The reflex need not wait for conscious choice.
- Information can still reach the brain.
No. Automatic spinal initiation does not require a conscious decision first, but information can also reach the brain and produce awareness.
Look for these in your work
- Separate initiation and awareness
- Avoid never-brain claim
Why should this simple drawing not be called a complete map of every withdrawal circuit?
Give me a hint
A teaching arc selects required stages.
Compare my reasoning
- It supplies one sensory-relay-motor route.
- Other connections and muscle coordination are not all drawn.
It is a simplified required route, not a complete map of every connection or muscle pair in real withdrawal circuits.
Look for these in your work
- Recognise the model scope
- Keep the required route useful
Common mistakes
- Making the receptor the contracting muscle.
- Saying automatic means the brain never receives information.
What can you explain now?
What produces movement in the supplied reflex?
Compare with the explanation
Muscle effector contraction
The neural pathway communicates with responding tissue.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Explain the withdrawal route and why automatic initiation does not exclude awareness.
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.