The epineurium is the outermost layer of dense irregular
connective tissue
Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...
surrounding a peripheral
nerve. It usually surrounds multiple
nerve fascicles as well as
blood vessels which supply the nerve. Smaller branches of these blood vessels penetrate into the
perineurium.
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 and
fibroblasts also play a vital role in maintenance and repair of the surrounding tissues.
When the
spinal nerve leaves the
vertebral canal
The spinal canal (or vertebral canal or spinal cavity) is the canal that contains the spinal cord within the vertebral column. The spinal canal is formed by the vertebrae through which the spinal cord passes. It is a process of the dorsal body ...
via an
intervertebral foramen, 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.
Clinical significance
A common
surgical procedure
Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pa ...
to repair a
torn nerve via the epineurium is termed an
epineurial repair
Epineurial repair is a common surgical procedure to repair a nerve laceration via the epineurium, the connective tissue surrounding nerve fibers originating from the spinal cord. It is intended to allow the restoration of sensory function. When a ...
.
Schwannomas often remain completely encapsulated by the epineurium as they grow.
Epineurial barriers can be used to limit the formation of
neuromas after
neurotmesis
Neurotmesis (in Greek tmesis signifies "to cut") is part of Seddon's classification scheme used to classify nerve damage. It is the most serious nerve injury in the scheme. In this type of injury, both the nerve and the nerve sheath are disrupted. ...
.
The epineurium is an effective barrier against
axon growth.
See also
*
Connective tissue in the peripheral nervous system
Nervous tissue, also called neural tissue, is the main tissue component of the nervous system. The nervous system regulates and controls body functions and activity. It consists of two parts: the central nervous system (CNS) comprising the bra ...
*
Perineurium
*
Endoneurium
*
Epimysium, a similar type of connective tissue which surrounds muscles
References
External links
* - "PNS, nerve (LM, Low)"
* - "PNS, nerve (LM, Medium)"
Diagram at Howard
{{Authority control
Neurohistology