Describe how a nerve impulse travels from a receptor to an effector in a simple reflex arc.

WJEC GCSE Biology (Wales) — 2.5.1 The nervous system · Describe · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The receptor senses a stimulus and generates a nerve impulse.
The impulse travels along a sensory neuron to the spinal cord.
In the spinal cord it synapses onto a relay neuron.
The impulse then travels along a motor neuron to the effector, producing a response.

Examiner tips

Use the exact sequence of steps; include receptor, sensory neuron, relay neuron, motor neuron and effector.
Show the direction of impulse (receptor → sensory → relay → motor → effector).
Mention the spinal cord as the site of the relay.
Use the term "nerve impulse" or "action potential" consistently.

Common mistakes

Omitting the relay neuron or the spinal cord.
Using the wrong order of neurons.
Confusing sensory and motor neurons.

Mark scheme (4 marks)

The receptor detects a stimulus and generates a nerve impulse
The impulse travels along a sensory neurone towards the spinal cord / CNS
The impulse passes through a relay neurone in the spinal cord / CNS
The impulse travels along a motor neurone to an effector, which produces a response

Key terms in this question

receptor · effector · reflex arc