Describe the roles of the central nervous system (CNS) and effectors in producing a response to a stimulus.

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 CNS, consisting of the brain and spinal cord, receives and processes information from receptors via sensory neurons. It then sends impulses through motor neurons to effectors. Effectors, which are either muscles or glands, carry out the response by producing the appropriate action.

Examiner tips

Use the exact terms ‘brain and spinal cord’, ‘sensory neurons’, ‘motor neurons’, and ‘effectors (muscles or glands)’
Show the flow: receptor → CNS → motor neuron → effector
Keep the answer concise and to the point

Common mistakes

Confusing the CNS with the PNS or omitting the spinal cord
Failing to mention that effectors can be muscles or glands
Using vague language such as ‘organism’ instead of ‘effectors’

Mark scheme (4 marks)

The CNS is made up of the brain and spinal cord
The CNS receives / processes information (from receptors / sensory neurones)
The CNS sends impulses (via motor neurones) to effectors
Effectors (muscles or glands) carry out the response / produce the action

Key terms in this question

central nervous system · effector · stimulus