In routine H&E staining of peripheral nerve, a cross-section shows individual axons surrounded by myelin (clear halos) and then a thin endoneurial sheath. Which cell is responsible for myelination in the peripheral nervous system and what is the ratio of myelinating cells to axons?

• A Oligodendrocytes; one cell myelinates multiple axons simultaneously
• B Satellite cells; one cell per axon in sympathetic ganglia
• C Schwann cells; one Schwann cell myelinates one segment of one axon (1:1 ratio) ✓
• D Astrocytes; one astrocyte supports multiple axons in a PNS nerve bundle

Explanation

In the peripheral nervous system, each myelinated axon segment (internode) is covered by a single Schwann cell that spirally wraps its plasma membrane around the axon multiple times. Each Schwann cell myelinates only ONE segment of ONE axon (1:1 relationship), in contrast to CNS oligodendrocytes which can myelinate segments of up to 50 different axons simultaneously. Unmyelinated axons in the PNS are embedded in Schwann cell cytoplasm without spiral wrapping (Remak bundles, up to 10 axons per Schwann cell). Nodes of Ranvier are the gaps between adjacent Schwann cell territories. Satellite cells surround neuronal cell bodies in ganglia.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.