Neurones are specialised cells that carry nerve impulses around the body. Compare the structure and function of sensory neurones and motor neurones.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (5 marks)
Sensory neurones carry impulses FROM receptors to the CNS, whereas motor neurones carry impulses FROM the CNS to effectors.
Sensory neurones have a long dendron (or dendrite) that carries the impulse from the receptor to the cell body.
Motor neurones have a long axon that carries the impulse from the cell body to the effector.
The cell body of a sensory neurone is located along the fibre (not at one end), usually near the receptor, while the cell body of a motor neurone is in the middle of the neurone.
Both types are surrounded by a myelin sheath, which speeds up the nerve impulse, and both have dendrites receiving impulses.
Sensory neurones have a long dendron (or dendrite) that carries the impulse from the receptor to the cell body.
Motor neurones have a long axon that carries the impulse from the cell body to the effector.
The cell body of a sensory neurone is located along the fibre (not at one end), usually near the receptor, while the cell body of a motor neurone is in the middle of the neurone.
Both types are surrounded by a myelin sheath, which speeds up the nerve impulse, and both have dendrites receiving impulses.
Examiner tips
- Use the command word ‘compare’ – list each feature for both types and then note the difference.
- Show the direction of impulse for each type – this is a key point in the mark scheme.
- Mention the myelin sheath – examiners reward the inclusion of this functional detail.
Common mistakes
- Confusing the direction of impulses – writing that sensory neurones carry impulses to effectors.
- Forgetting that the sensory neurone’s cell body is not at the end of the fibre.
- Leaving out the myelin sheath or describing it incorrectly.
Mark scheme (5 marks)
- Sensory neurones carry impulses FROM receptors (to the CNS) / motor neurones carry impulses FROM the CNS (to effectors)
- Sensory neurones have a long dendron / long fibre carrying the impulse from the receptor to the cell body
- Motor neurones have a long axon / long fibre carrying the impulse from the cell body to the effector
- The cell body of a sensory neurone is located along / to the side of the fibre (not at one end) / cell body is in the middle of the neurone
- Both types are surrounded by / have a myelin sheath (which speeds up the nerve impulse) OR both have dendrites receiving impulses
Key terms in this question
sensory neurone · motor neurone
Related
- All WJEC A-Level Biology (Wales) revision notes →
- How to answer a "Compare" question →
- Decode the mark scheme abbreviations →
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