GROSS ANATOMY

Detailed explanation-1: -Within a nerve, each axon is surrounded by a layer of connective tissue called the endoneurium. The axons are bundled together into groups called fascicles. Each fascicle is wrapped in a layer of connective tissue called the perineurium.

Detailed explanation-2: -Perineurium isolates groups of axon-Schwann cell units to form nerve fascicles and constitutes the main diffusion barrier between the endoneurium and the extrafascicular tissues. Perineurium is composed of concentric layers of large, flat perineurial cells.

Detailed explanation-3: -Epineurium. Epineurium is the interfascicular connective tissue layer. It lies between and around the secondary fascicles and forms a sheath encircling all peripheral nerve trunks. The epineurium is a continuation of the dura mater that extends to the ends of the peripheral nerves.

Detailed explanation-4: -The perineurium is a multilayered structure of flattened cells derived from fibroblasts. Each layer of the perineurium is invested by basement membrane on both sides. Hence, in contrast to classic epithelial tissue, the perineurium does not display an apicobasal polarity.

Detailed explanation-5: -On the outside of each peripheral nerve, there is collagenous tissue: epineurium. Surrounding every fascicle within the nerve is the perineurium. Individual nerve fibers within the fascicles are embedded in endoneurium, which fills the space bound by the perineurium.