The fluid component of the peripheral nervous system is derived from the blood. Let us therefore concentrate on the blood supply of peripheral nerve and ganglia in order to understand the structural basis for endoneurial fluid formation. The vessels are concerned with exchange of gases, nutrients and metabolic waste products, the maintenance of the blood-nerve barrier and the volume and pressure regulation of endoneurial fluid. Cardinal features of these vessels are the richness of anastomoses and the presence of microvascular networks or plexuses. Nutrient arteries from adjacent large vessels give off many small branches, which by anastomoses form the epineurial and perineurial vascular plexuses.
Numerous vessels pierce the perineurium to join the endoneurial vascular network.
This is composed of many small vessels running mainly in the longitudinal direction along the nerves. They emphasized that the small endoneurial vessels, i.e. the capillaries were wider and more widely spaced than in muscle. The rabbit nerves contained vessels which were special in many respects. The spatial distribution of capillaries has also been investigated in rat nerves and described in a small but important paper by Nukada et al. They found that the vessels were unevenly distributed in the fascicles.