Compare the three neurone roles within a reflex pathway
Trace incoming information central connection and outgoing instructions.
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
Which stage is the final response-producing structure?
What you will learn
- Follow the pathway by function
- Keep cell role separate from the whole system
Compare the three neurone roles within a reflex pathway
Sensory, relay and motor are communication roles between the separate receptor and effector in the specified simple arc. Original teaching model.
| Feature | Meaning |
|---|---|
| Sensory | Input from receptor towards CNS |
| Relay | Connection within CNS |
| Motor | Output from CNS towards effector |
| Effector | Muscle contraction or gland secretion |
Follow the pathway by function
A simple three-neurone reflex pathway uses sensory, relay and motor neurones in sequence. Sensory information travels from a receptor towards central structures. A relay neurone connects the central incoming and outgoing pathways, and a motor neurone conducts towards the effector. Each role is defined through its connection and contribution to the pathway.
The receptor and effector are additional required parts, not fourth and fifth neurone types in this list. A receptor detects the stimulus, while an effector performs the response. In a withdrawal example, the muscle is an effector and contraction is its response; the motor neurone supplies communication rather than being the whole muscle itself.
Keep cell role separate from the whole system
A central relay connects neurones within CNS tissue in the supplied spinal model. Peripheral sensory and motor routes connect that central circuit with body structures. Do not call the relay neurone a long urine-carrying tube or describe all three types as having exactly the same direction relative to CNS. The incoming and outgoing roles differ.
This comparison describes the specified three-neurone arc, not a universal count for every reflex in mammals. Some real reflex circuits have different organisation, and a general cell outline alone does not establish function. Use the complete supplied receptor-to-effector context and distinguish communication stages from detection and the final tissue action.
Sources for this lesson
Pause and explain
Which ordered cell roles fit the supplied arc?
Worked example
Give the ordered neurone roles between receptor and effector in the supplied arc.
Show the worked solution
- Start with incoming sensory communication.
- Then central relay and outgoing motor communication.
Answer Sensory neurone → relay neurone → motor neurone.
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Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
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.
Compare the three neurone roles in the supplied simple reflex pathway.
Give me a hint
Give each role and direction.
Compare my reasoning
- Sensory carries receptor information towards CNS; relay connects within CNS.
- Motor carries instructions towards effector.
Sensory: receptor towards CNS. Relay: connects neurones within CNS. Motor: CNS towards effector.
Look for these in your work
- Name all three roles
- Use their distinct connections
Is the muscle effector an additional motor neurone?
Give me a hint
A communicating cell and responding tissue differ.
Compare my reasoning
- Motor neurone supplies a signal.
- Muscle carries out contraction.
No. The motor neurone communicates with a separate muscle effector; muscle contraction is the response.
Look for these in your work
- Separate cell and tissue
- State contraction
May a description of this three-neurone model be used to claim every mammalian reflex has exactly three neurones?
Give me a hint
A supplied example is not every circuit.
Compare my reasoning
- The model specifies a sensory-relay-motor route.
- Other reflex circuit arrangements exist.
No. Describe this specified simple arc; its three-neurone organisation is not a universal count for every mammalian reflex.
Look for these in your work
- Keep the supplied model
- Avoid universal circuit count
Common mistakes
- Counting receptor and effector as two extra neurone types.
- Assuming every possible reflex has exactly this circuit.
What can you explain now?
Which ordered cell roles fit the supplied arc?
Compare with the explanation
Sensory → relay → motor
Incoming, central connection, outgoing.
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Make it stick
Compare the three neurone roles and keep receptor and effector distinct.
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.