For this reason, metabolic disorders of myelin lipids, such as metachromatic leukodystrophy, affect both the central white matter and peripheral nerves. The myelin sheath acts as an electrical insulator, preventing short-circuiting between axons. More important, it facilitates conduction. The nodes of Ranvier are the only points where the axon is uncovered and ions can be exchanged between it and the extracellular fluid. Peripheral nerves consist of many fascicles that contain myelinated and unmyelinated axons.
Endoneurium is the small amount of collagen that is present between individual axons.
Perineurium is a sheath of special, fiber-like cells that ties the axons of each fascicle together. Epineurium is the connective tissue that surrounds the entire trunk of a peripheral nerve and gives off vascular connective tissue septa that traverse the nerve and separate fascicles from one another. Wallerian degeneration . The neuronal cell body maintains the axon through the axoplasmic flow. When an axon is transected, its distal part, including its myelin sheath, undergoes a series of changes leading to its complete structural disintegration and chemical degradation.