# Explain how the structure of a myelinated motor neurone allows for rapid transmission of nerve impulses compared with an unmyelinated neurone.

> IB DP Biology Higher Level (2023 syllabus) — C2.2 Neural signalling · Explain · 4 marks

## Mark scheme (4 marks)

1. Myelin sheath is formed by Schwann cells wrapping around the axon, acting as an electrical insulator
2. Depolarisation / ion exchange can only occur at nodes of Ranvier (gaps between myelin sheaths) where the axon membrane is exposed
3. The impulse effectively 'jumps' from node to node (saltatory conduction), covering larger distances per depolarisation event
4. This significantly increases conduction velocity compared with an unmyelinated axon, in which depolarisation must occur continuously along the entire length of the membrane

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