Peripheral nerve: endoneurium, perineurium, epineurium; myelin !

Tissue

A peripheral nerve is a cable of many axons, each with its Schwann cells, bundled by three layers of connective tissue.

Updated 2026-11-01

See it in 3D: Sciatic nerve · Median nerve · Ulnar nerve · Radial nerve

What it is

Peripheral nerves carry motor, sensory and autonomic axons between the central nervous system and the body. Their axons, myelinated or not, are wrapped by Schwann cells and grouped into fascicles by three connective tissue sheaths. Large myelinated fibres conduct fastest because the action potential jumps from node to node.

Key facts

Each Schwann cell myelinates one internode of one axon.
Nodes of Ranvier concentrate voltage-gated sodium channels; saltatory conduction is faster and saves energy.
Fibre diameter and myelin thickness set conduction speed: large myelinated A-alpha motor fibres fastest, thin unmyelinated C fibres slowest.
Nerve conduction studies measure velocity (slowed by demyelination) and amplitude (reduced by axon loss).

Structure

Epineurium: dense irregular connective tissue with fat and vessels around the whole nerve and between its fascicles.
Perineurium: several layers of flattened perineurial cells joined by tight junctions around each fascicle; it forms the blood–nerve barrier.
Endoneurium: loose, delicate connective tissue (reticular fibres) around each individual axon and its Schwann cell.
Cross section on H&E: round fascicles of small dots (axons) each surrounded by a pale ring (dissolved myelin) and scattered Schwann cell nuclei.
Longitudinal section: wavy, zigzag fibres with elongated Schwann nuclei; nodes of Ranvier show as narrow constrictions.
Unmyelinated fibres (pain and autonomic C fibres) sit in groups inside grooves of one Schwann cell (Remak bundles).

Clinical notes

Carpal tunnel syndrome: compression of the median nerve under the flexor retinaculum causes focal demyelination first (slowed conduction, night tingling in the thumb, index and middle fingers), then axon loss and thenar wasting.
Ulnar nerve compression at the elbow (cubital tunnel) is the second most common entrapment of the arm.
Diabetic neuropathy, the most common peripheral neuropathy, starts in the longest axons, giving a stocking-and-glove sensory loss.
Leprosy, still seen in Colombia, infects Schwann cells and thickens nerves, causing numb skin patches.

Test yourself

Think of the answer, then tap the question to see it.

Which nerve sheath forms the blood–nerve barrier?

The perineurium, whose flattened cells are joined by tight junctions around each fascicle.

What surrounds each individual axon in a peripheral nerve?

The endoneurium, a delicate loose connective tissue, outside the axon's Schwann cell and its basal lamina.

Why do myelinated fibres conduct faster than unmyelinated ones?

Myelin insulates the internodes, so the action potential is regenerated only at the nodes of Ranvier and jumps from node to node (saltatory conduction).

In carpal tunnel syndrome, what happens to the median nerve over time?

Compression first causes focal demyelination with slowed conduction and tingling; prolonged compression causes axon loss, numbness and thenar muscle weakness.

Add to my cards (4)

See it in 3D

The structures of Durgical's 3D anatomy where it is found.

← All of histology

Educational content on normal microscopic structure and its clinical relevance; no substitute for studying slides or for a health professional's advice.

Sources: 13.4 The Peripheral Nervous System (OpenStax, 2022); 12.2 Nervous Tissue (OpenStax, 2022); Carpal Tunnel Syndrome (MedlinePlus, U.S. National Library of Medicine, 2024); Peripheral Nerve Disorders (MedlinePlus, U.S. National Library of Medicine, 2024).

Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake

Representative model, for educational purposes only.