The epineurium is the outermost layer of dense irregular
connective tissue 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
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 and
fibroblasts
A fibroblast is a type of biological cell that synthesizes the extracellular matrix and collagen, produces the structural framework ( stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells ...
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 c ...
via an
intervertebral foramen
The intervertebral foramen (also called neural foramen, and often abbreviated as IV foramen or IVF) is a foramen between two spinal vertebrae. Cervical, thoracic, and lumbar vertebrae all have intervertebral foramina.
The foramina, or openi ...
, two layers of the
spinal meninges, the
arachnoid
Arachnoid may refer to:
* Relating to arachnids
* Arachnoid (astrogeology), a geological structure found only on the planet Venus
* Arachnoid (botany), referring to organs with a cobwebby exterior appearance
* Arachnoid granulation, small protrus ...
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 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 n ...
.
Schwannomas
A schwannoma (or neurilemmoma) is a usually benign nerve sheath tumor composed of Schwann cells, which normally produce the insulating myelin sheath covering peripheral nerves.
Schwannomas are homogeneous tumors, consisting only of Schwann cells. ...
often remain completely encapsulated by the epineurium as they grow.
Epineurial barriers can be used to limit the formation of
neuromas
A neuroma (; plural: neuromata or neuromas) is a growth or tumor of nerve tissue. Neuromas tend to be benign tumor, benign (i.e. not malignant, cancerous); many Nervous tissue#Tumours, nerve tumors, including those that are commonly malignant, ar ...
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
An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
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 brain ...
*
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 ...
*
Endoneurium
The endoneurium (also called endoneurial channel, endoneurial sheath, endoneurial tube, or Henle's sheath) is a layer of delicate connective tissue around the myelin sheath of each myelinated nerve fiber in the peripheral nervous system. Its com ...
*
Epimysium
Epimysium (plural ''epimysia'') (Greek ''epi-'' for on, upon, or above + Greek ''mys'' for muscle) is the fibrous tissue envelope that surrounds skeletal muscle. It is a layer of dense irregular connective tissue which ensheaths the entire muscle ...
, 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