Which layer surrounds individual axons?

Which layer surrounds individual axons?

• A. Perineurium
• B. Endoneurium
• C. Epineurium
• D. Meninges

Answer: (B)

In peripheral nerves, each axon is wrapped by its own delicate protective layer, the endoneurium. This thin connective tissue surrounds individual axons (and their Schwann cell coverings and myelin), providing a microenvironment with capillaries to nourish the fiber and a bit of mechanical support. Surrounding groups of axons into bundles called fascicles is the perineurium, which forms a diffusion barrier and helps maintain the internal milieu of the fascicle. The entire nerve, with all its fascicles, is encased by the epineurium, a tougher outer sheath. The meninges are protective coverings of the brain and spinal cord, not part of peripheral nerves.

In peripheral nerves, each axon is wrapped by its own delicate protective layer, the endoneurium. This thin connective tissue surrounds individual axons (and their Schwann cell coverings and myelin), providing a microenvironment with capillaries to nourish the fiber and a bit of mechanical support. Surrounding groups of axons into bundles called fascicles is the perineurium, which forms a diffusion barrier and helps maintain the internal milieu of the fascicle. The entire nerve, with all its fascicles, is encased by the epineurium, a tougher outer sheath. The meninges are protective coverings of the brain and spinal cord, not part of peripheral nerves.