# Describe the roles of the three types of neurone found in the nervous system, and explain one structural adaptation of a neurone that allows nerve impulses to travel quickly.

> Eduqas A-Level Biology — 4.6 The nervous system · Describe · 5 marks

## Mark scheme (5 marks)

1. Sensory neurone carries impulses from a receptor to the spinal cord / brain (CNS)
2. Relay neurone carries impulses between different parts of the central nervous system
3. Motor neurone carries impulses from the CNS to an effector (muscle or gland)
4. Named structural adaptation: myelin sheath (made of Schwann cells) surrounds the axon
5. Explanation of how the named adaptation speeds up the impulse: myelin sheath provides electrical insulation which speeds up the nerve impulse / long axon reduces the number of synapses so fewer slow-downs occur / dendrites pick up impulses from multiple neurones

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