Cambridge O Level Biology · Syllabus 5090 · Coordination and Control
Sensory Neurone
What is Sensory Neurone?
A neurone that carries electrical impulses from a receptor to the central nervous system. In a simplified diagram it is recognised by a cell body lying part-way along the fibre, on a short side branch, rather than at either end.
This definition is part of the Coordination and Control chapter in Cambridge O Level Biology.
Common mistakes with Sensory Neurone
- Nerve or neurone? These are not synonyms and the exam distinguishes them. A neurone is a single nerve cell. A nerve is a bundle containing the fibres of many neurones, wrapped together in connective tissue. So the peripheral nervous system is made of nerves, and each nerve contains many neurones. Writing "a nerve carries an impulse to the CNS" is loose; "a sensory neurone carries an impulse to the CNS" is precise, and precise is what gets the mark.
- A wiring point students invent. Not every pathway contains all three neurones, and the syllabus does not claim it does. What you must be able to describe is the reflex arc, which does contain all three. Do not write that a sensory neurone connects directly to a muscle: sensory neurones end in the CNS, and the instruction to a muscle always leaves along a motor neurone.
Questions students ask about Sensory Neurone
What is the order of a reflex arc?
Stimulus, receptor, sensory neurone, relay neurone in the central nervous system, motor neurone, effector, response. The effector is a muscle or a gland, and the impulse never travels backwards along this pathway.
Last reviewed Syllabus 2026-2028