# Explain how the ultrastructure of a myelinating Schwann cell is adapted for its function in the peripheral nervous system.

> IB DP Biology Higher Level (2023 syllabus) — B2.3 Cell specialisation · Explain · 4 marks

## Mark scheme (4 marks)

1. Schwann cells wrap multiple layers of their plasma membrane around the axon, forming the myelin sheath
2. The cytoplasm is largely displaced / compressed out during wrapping, leaving tightly packed lipid bilayers that act as electrical insulation
3. Gaps between adjacent Schwann cells form nodes of Ranvier, allowing saltatory conduction which greatly increases the speed of nerve impulse transmission
4. Schwann cells are rich in mitochondria / have metabolic activity to support the energy demands of membrane synthesis and maintenance of the sheath / active support of axon

## Key terms

- [Schwann cell](https://www.gradenine.co.uk/glossary/schwann-cell)

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-ultrastructure-of-a-0aaeeb6e) · Published by Druglandscape Ltd.