The epineurium is the outermost layer of dense irregular

connective tissue Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesod ...

surrounding a peripheral

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

. It usually surrounds multiple

nerve fascicle A nerve fascicle is a bundle of nerve fibers belonging to a nerve in the peripheral nervous system. A nerve fascicle is also called a fasciculus, as is a nerve tract in the central nervous system. A nerve fascicle is enclosed by perineurium, a l ...

s as well as

blood vessels Blood vessels are the tubular structures of a circulatory system that transport blood throughout many animals’ bodies. Blood vessels transport blood cells, nutrients, and oxygen to most of the tissues of a body. They also take waste an ...

which supply the nerve. Smaller branches of these blood vessels penetrate into the

perineurium The perineurium is a protective sheath that surrounds a nerve fascicle. This bundles together axons targeting the same anatomical location. The perineurium is composed from fibroblasts. In the peripheral nervous system, the myelin sheath of each ...

. In addition to blood vessels which supply the nerve, lymphocytes and fibroblasts are also present and contribute to the production of collagen fibers that form the backbone of the epineurium. In addition to providing structural support,

lymphocytes A lymphocyte is a type of white blood cell (leukocyte) in the immune system of most vertebrates. Lymphocytes include T cells (for cell-mediated and cytotoxic adaptive immunity), B cells (for humoral, antibody-driven adaptive immunity), and ...

and

fibroblasts A fibroblast is a type of biological cell typically with a spindle shape that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibrobla ...

also play a vital role in maintenance and repair of the surrounding tissues. When the

spinal nerve A spinal nerve is a mixed nerve, which carries Motor neuron, motor, Sensory neuron, sensory, and Autonomic nervous system, autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each s ...

leaves the vertebral canal via an

intervertebral foramen The intervertebral foramen (also neural foramen) (often abbreviated as IV foramen or IVF) is an opening between (the intervertebral notches of) two pedicles (one above and one below) of adjacent vertebra in the articulated spine. Each interve ...

, two layers of the spinal meninges, the arachnoid and the dura invaginate the nerve to form a dural sleeve of connective tissue, which is the epineurium. The outer portion of this sleeve comprises the external epineurium which permits longitudinal nerve excursion and absorption of longitudinal stress. The layer of the epineurium that extends within the nerve to define the fascicles is termed the internal epineurium. Together, these two layers form the epineurium, which varies in thickness along the course of a nerve. The epineurium is usually most abundant around joints, as its function is to protect the nerves from stretching and subsequent injury. Epineurium is primarily made from

collagen Collagen () is the main structural protein in the extracellular matrix of the connective tissues of many animals. It is the most abundant protein in mammals, making up 25% to 35% of protein content. Amino acids are bound together to form a trip ...

Clinical significance

A common

surgical procedure Surgery is a medical specialty that uses manual and instrumental techniques to diagnose or treat pathological conditions (e.g., trauma, disease, injury, malignancy), to alter bodily functions (e.g., malabsorption created by bariatric surgery s ...

to repair a torn nerve via the epineurium is termed an epineurial repair. Schwannomas often remain completely encapsulated by the epineurium as they grow. Epineurial barriers can be used to limit the formation of neuromas after neurotmesis. The epineurium is an effective barrier against

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

growth.

References

External links

* - "PNS, nerve (LM, Low)" * - "PNS, nerve (LM, Medium)"
Diagram at Howard
{{Authority control Neurohistology

Clinical significance

See also

References

External links