Figure 2.

Peripheral nerve structure. The endoneurium is the innermost layer and consists of nerve fibers, composed of axons surrounded by different subtypes of Schwann Cells (myelinating and non–myelinating Schwann cells); it also contains blood vessels, resident macrophages and fibroblasts [56]. The perineurium, which surrounds the endoneurium, is a layer of cylindrical cells tightly interconnected with tight and gap junctions, forming a protective barrier [57]. The epineurium is the outermost layer surrounding several nerve bundles; it includes an elastin and collagen sheath, blood and lymphatic vessels, resident macrophages and mast cells, fibroblasts. The epineurium is itself–innervated by small axons deriving from the endoneurium [58].