On electron microscopy of a peripheral nerve, a single Schwann cell is found to envelop multiple unmyelinated axons. This arrangement is seen in which type of fiber?

• A A-beta fibers (large myelinated touch fibers)
• B Remak bundle (C fibers — unmyelinated, slow pain and autonomic postganglionic fibers) ✓
• C A-alpha motor fibers
• D Ia afferent spindle fibers

Explanation

Unmyelinated C fibers (carrying slow pain, temperature, and autonomic postganglionic signals) are grouped in Remak bundles — multiple unmyelinated axons ensheathed by a single Schwann cell without forming a myelin spiral. This is distinct from myelinated fibers, where each Schwann cell forms a single myelin sheath around one axon segment (internode). A-alpha, A-beta, and Ia fibers are all large myelinated fibers with individual Schwann cell myelination.

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

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Written and medically reviewed by the StethoPrep medical team.