View source for Spinal nerve

{{Short description|Nerve that carries signals between the spinal cord and the body}}
{{Infobox nerve
| Name        = Spinal nerve
| Latin       = nervus spinalis
| Image       = spinal nerve.svg
| Caption     = The formation of the spinal nerve from the posterior and anterior roots
| Image2      =
| Innervates  =
| BranchFrom  =
| BranchTo    =
}}
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 [[nerve]]s, one on each side of the [[vertebral column]].<ref name="Kaiser">{{cite book |last1=Kaiser |first1=JT |last2=Lugo-Pico |first2=JG |title=Neuroanatomy, Spinal Nerves. |date=January 2024 |pmid=31194375}}</ref><ref name="AANS">{{cite web |title=A Neurosurgeon’s Overview of the Anatomy of the Spine and Peripheral Nervous System |url=https://www.aans.org/en/Patients/Neurosurgical-Conditions-and-Treatments/Anatomy-of-the-Spine-and-Peripheral-Nervous-System |website=www.aans.org |access-date=21 December 2023 |language=en}}</ref> These are grouped into the corresponding [[cervical vertebrae|cervical]], [[thoracic vertebrae|thoracic]], [[lumbar vertebrae|lumbar]], [[sacral vertebrae|sacral]] and [[coccygeal vertebrae|coccygeal]] regions of the spine.<ref name="Kaiser"/> There are eight pairs of '''cervical nerves''', twelve pairs of '''thoracic nerves''', five pairs of '''lumbar nerves''', five pairs of '''sacral nerves''', and one pair of '''coccygeal nerves'''. The spinal nerves are part of the [[peripheral nervous system]].<ref name="Kaiser" />

== Structure ==

[[File:Gray675.png|thumb|left|240px|Spinal nerve]]
[[File:Cervical vertebra english.png|thumb|240px|Typical spinal nerve location]]
Each spinal nerve is a [[mixed nerve]], formed from the combination of [[nerve root]] [[axon|fibers]] from its  [[Dorsal root of spinal nerve|dorsal]] and [[Ventral root of spinal nerve|ventral roots]]. The dorsal root is the [[afferent nerve fiber|afferent]] sensory root and carries sensory information to the brain. The ventral root is the [[efferent nerve fiber|efferent]] motor root and carries motor information from the brain. The spinal nerve emerges from the spinal column through an opening ([[intervertebral foramen]]) between adjacent vertebrae. This is true for all spinal nerves except for the first spinal nerve pair (C1), which emerges between the [[occipital bone]] and the [[Atlas (anatomy)|atlas]] (the first vertebra).<ref name="Saladin1">{{cite book |last1=Saladin |first1=Kenneth S. |title=Human anatomy |date=2011 |publisher=McGraw-Hill |location=New York |isbn=9780071222075 |pages=382–388|edition=3rd}}</ref> Thus the cervical nerves are numbered by the vertebra below, except spinal nerve C8, which exists below vertebra C7 and above vertebra T1. The thoracic, lumbar, and sacral nerves are then numbered by the vertebra above. In the case of a [[Lumbar vertebrae#Variation|lumbarized]] S1 vertebra (also known as L6) or a [[Lumbar vertebrae#Variation|sacralized]] L5 vertebra, the nerves are typically still counted to L5 and the next nerve is S1.

[[File:Gray799.svg|thumb|right|300px|Scheme showing structure of a typical spinal nerve<br />1. [[General somatic efferent fibers|Somatic efferent]].<br />2. [[General somatic afferent fibers|Somatic afferent]].<br />3,4,5. [[General visceral efferent fibers|Sympathetic efferent]].<br />6,7. [[General visceral afferent fibers|Autonomic afferent]].]]
Outside the vertebral column, the nerve divides into branches. The [[dorsal ramus of spinal nerve|dorsal ramus]] contains nerves that serve the posterior portions of the trunk carrying visceral motor, somatic motor, and somatic sensory information to and from the skin and muscles of the back ([[epaxial muscles]]). The [[ventral ramus]] contains nerves that serve the remaining anterior parts of the trunk and the upper and lower limbs ([[hypaxial muscles]]) carrying visceral motor, somatic motor, and sensory information to and from the ventrolateral body surface, structures in the body wall, and the limbs. The [[Meningeal branches of spinal nerve|meningeal branches (recurrent meningeal or sinuvertebral nerves)]] branch from the spinal nerve and re-enter the intervertebral foramen to serve the ligaments, dura, blood vessels, intervertebral discs, facet joints, and periosteum of the vertebrae. The [[rami communicantes]] contain autonomic nerves that serve visceral functions carrying visceral motor and sensory information to and from the visceral organs.

Some anterior rami merge with adjacent anterior rami to form a [[nerve plexus]], a network of interconnecting nerves. Nerves emerging from a plexus contain fibers from various spinal nerves, which are now carried together to some target location. The [[spinal plexus]]es are the [[cervical plexus]], [[brachial plexus]], [[lumbar plexus]], the [[sacral plexus]] and the much smaller [[coccygeal plexus]].<ref name="Saladin1" />

== Regional nerves ==
{{Further |Spinal cord#Spinal cord segments}}

=== Cervical nerves ===

[[File:Gray795.png|thumb|Cervical nerves]]

The cervical nerves are the spinal nerves from the cervical vertebrae in the [[Spinal cord#Spinal cord segments|cervical segment]] of the spinal cord. Although there are seven cervical vertebrae (C1–C7), there are eight cervical nerves [[cervical spinal nerve 1|C1]]–[[cervical spinal nerve 8|C8]]. C1–C7 emerge above their corresponding vertebrae, while C8 emerges below the C7 vertebra. Everywhere else in the spine, the nerve emerges below the vertebra with the same name.

The posterior distribution includes the [[suboccipital nerve]] (C1), the [[greater occipital nerve]] (C2) and the [[third occipital nerve]] (C3). The anterior distribution includes the [[cervical plexus]] (C1–C4) and [[brachial plexus]] (C5–T1).

The cervical nerves innervate the [[sternohyoid muscle|sternohyoid]], [[sternothyroid muscle|sternothyroid]] and [[omohyoid muscle]]s.

A loop of nerves called [[ansa cervicalis]] is part of the cervical plexus.

=== Thoracic nerves ===

The thoracic nerves are the twelve spinal nerves emerging from the thoracic vertebrae. Each thoracic nerve T1–T12 originates from below each corresponding [[thoracic vertebra]]. Branches also exit the spine and go directly to the [[paravertebral ganglia]] of the [[autonomic nervous system]] where they are involved in the functions of organs and glands in the head, neck, thorax and abdomen.

==== Anterior divisions ====
The [[intercostal nerves]] come from thoracic nerves T1–T11, and run between the ribs. At T2 and T3, further branches form the [[intercostobrachial nerve]]. The [[subcostal nerve]] comes from nerve T12, and runs below the twelfth rib.

====Posterior divisions====
The medial branches (ramus medialis) of the posterior branches of the upper six thoracic nerves run between the [[semispinalis dorsi]] and [[multifidus]], which they supply; they then pierce the [[rhomboid muscle|rhomboid]] and [[trapezius muscle]]s, and reach the skin by the sides of the spinous processes. This sensitive branch is called the medial cutaneous ramus.

The medial branches of the lower six are distributed chiefly to the multifidus and [[longissimus dorsi]], occasionally they give off filaments to the skin near the middle line. This sensitive branch is called the posterior cutaneous ramus.

=== Lumbar nerves ===
[[File:Gray823.png|thumb|Lumbar plexus and branches]]
The [[lumbar nerves]] are the five spinal nerves emerging from the lumbar vertebrae. They are divided into posterior and anterior divisions.

====Posterior divisions====
The medial branches of the posterior divisions of the lumbar nerves run close to the articular processes of the vertebrae and end in the [[multifidus muscle]].

The laterals supply the [[erector spinae muscles]].

The upper three give off cutaneous nerves which pierce the aponeurosis of the [[latissimus dorsi]] at the lateral border of the erector spinae muscles, and descend across the posterior part of the [[iliac crest]] to the skin of the [[buttock]], some of their twigs running as far as the level of the [[greater trochanter]].

==== Anterior divisions ====
The anterior divisions of the lumbar nerves (rami anteriores) increase in size from above downward. They are joined, near their origins, by [[gray rami communicantes]] from the [[lumbar ganglia]] of the [[sympathetic trunk]]. These rami consist of long, slender branches which accompany the [[lumbar arteries]] around the sides of the vertebral bodies, beneath the [[psoas major]]. Their arrangement is somewhat irregular: one ganglion may give rami to two lumbar nerves, or one lumbar nerve may receive rami from two [[ganglia]].

The first and second, and sometimes the third and fourth lumbar nerves are each connected with the lumbar part of the sympathetic trunk by a [[white ramus communicans]].

The nerves pass obliquely outward behind the psoas major, or between its [[Muscle fascicle|fasciculi]], distributing filaments to it and the [[quadratus lumborum]].

The first three and the greater part of the fourth are connected together in this situation by anastomotic loops, and form the [[lumbar plexus]].

The smaller part of the fourth joins with the fifth to form the [[lumbosacral trunk]], which assists in the formation of the [[sacral plexus]]. The fourth nerve is named the [[furcal nerve]], from the fact that it is subdivided between the two plexuses.

=== Sacral nerves ===

[[File: Gray828.png|thumb|Plan of sacral and pudendal plexuses]]
The '''sacral nerves''' are the five pairs of spinal nerves which exit the [[sacrum]] at the lower end of the [[Human vertebral column|vertebral column]]. The roots of these nerves begin inside the vertebral column at the level of the [[L1 vertebra]], where the [[cauda equina]] begins, and then descend into the sacrum.<ref name="ReferenceA">1. '''Anatomy, descriptive and surgical: Gray's anatomy'''. Gray, Henry. Philadelphia : Courage Books/Running Press, 1974</ref><ref>2. '''Clinically Oriented Anatomy'''. Moore, Keith L. Philadelphia : Wolters Kluwer Health/Lippincott Williams & Wilkins, 2010 (6th ed)</ref>

There are five paired sacral nerves, half of them arising through the sacrum on the left side and the other half on the right side. Each nerve emerges in two divisions: one division through the [[anterior sacral foramina]] and the other division through the [[posterior sacral foramina]].<ref name="ReferenceA"/>

The nerves divide into branches and the branches from different nerves join with one another, some of them also joining with lumbar or coccygeal nerve branches. These anastomoses of nerves form the [[sacral plexus]] and the [[lumbosacral plexus]]. The branches of these plexus give rise to nerves that supply much of the [[hip]], [[thigh]], [[leg]] and [[foot]].<ref name="ReferenceA"/><ref name="ReferenceB">3. '''Human Neuroanatomy'''. Carpenter, Malcolm B. Baltimore : Williams & Wilkins Co., 1976 (7th ed)</ref>

The sacral nerves have both [[Afferent nerve fiber|afferent]] and [[efferent fibers]], thus they are responsible for part of the [[sensory perception]] and the movements of the lower extremities of the human body. From the S2, S3 and S4 arise the pudendal nerve and parasympathetic fibers whose electrical potential supply the [[descending colon]] and [[rectum]], [[urinary bladder]] and [[genital organs]]. These pathways have both afferent and efferent fibers and, this way, they are responsible for conduction of sensory information from these pelvic organs to the [[central nervous system]] (CNS) and motor impulses from the CNS to the pelvis that control the movements of these pelvic organs.<ref name="ReferenceB"/>

=== Coccygeal nerves ===

The bilateral coccygeal nerves, Co, are the 31st pair of spinal nerves. It arises from the conus medullaris, and its ventral ramus helps form the [[coccygeal plexus]]. It does not divide into a medial and lateral branch. Its fibers are distributed to the skin superficial and posterior to the [[coccyx]] bone via the [[anococcygeal nerve]] of the coccygeal nerve plexus.

== Function ==

[[File:Gray802.png|thumb|right| Areas of distribution of the cutaneous branches of the posterior divisions of the spinal nerves. The areas of the medial branches are in black, those of the lateral in red]]
{{Actions by spinal nerves}}
{{Clear}}

==Spinal plexuses==

A [[spinal plexus]] is a weblike [[nerve plexus]] formed by the [[Ventral ramus of spinal nerve|anterior nerve roots]] that branch and [[anastomoses|merge]] repeatedly. The only region that does not have a plexus is the thoracic region. The small [[cervical plexus]] is in the neck, the [[brachial plexus]] is in the shoulder, the [[lumbar plexus]] is in the lower back, beneath this is the [[sacral plexus]], and next to the lower sacrum and [[coccyx]] is the very small [[coccygeal plexus]].<ref name="Saladin1"/>

== Clinical significance ==

The muscles that one particular spinal root supplies are that nerve's [[myotome (anatomy)|myotome]], and the [[dermatome (anatomy)|dermatomes]] are the areas of sensory innervation on the skin for each spinal nerve. Lesions of one or more nerve roots result in typical patterns of neurologic defects ([[muscle weakness]], abnormal sensation, changes in reflexes) that allow localization of the responsible lesion.

There are several procedures used in [[sacral nerve stimulation]] for the treatment of various related disorders.

[[Sciatica]] is generally caused by the compression of lumbar nerves L4, or L5 or sacral nerves S1, S2, or S3, or by compression of the sciatic nerve itself.

== Gallery ==

<gallery>
 File:Gray796.png|A portion of the spinal cord, showing its right lateral surface. The dura is opened and arranged to show the nerve roots.
 File:Gray797.png|Distribution of the cutaneous nerves. Ventral aspect.
 File:Gray798.png|Distribution of the cutaneous nerves. Dorsal aspect.
 File:Sobo 1909 611.png|The spinal cord with [[dura mater|dura]] cut open, showing the exits of the spinal nerves.
 File:Sobo 1909 613.png|The spinal cord showing how the anterior and posterior roots join in the spinal nerves.
 File:Sobo 1909 614.png|A longer view of the spinal cord.
 File:Sobo 1909 615.png|Projections of the spinal cord into the nerves (red motor, blue sensory).
 File:Sobo 1909 616.png|Projections of the spinal cord into the nerves (red motor, blue sensory).
 File:Cervical plexus.gif|Schematic diagram of cervical plexus.
</gallery>
<gallery caption="Dissection images">
File:Slide2PIT.JPG|Cerebrum. Inferior view. Deep dissection.
File:Slide3PIT.JPG|Cerebrum. Inferior view. Deep dissection.
File:Slide2VAS.JPG|Spinal nerves. Spinal cord and vertebral canal. Deep dissection.
</gallery>

== See also ==
* [[Plexus]]
* [[Nerve plexus]]
:* [[Brachial plexus]]
* [[Cranial nerves]]

== References ==
{{reflist}}
{{refbegin}}

* Blumenfeld H. 'Neuroanatomy Through Clinical Cases'. Sunderland, Mass: Sinauer Associates; 2002.
* Drake RL, Vogl W, Mitchell AWM. 'Gray's Anatomy for Students'. New York: Elsevier; 2005:69-70.
* Ropper AH, Samuels MA. 'Adams and Victor's Principles of Neurology'. Ninth Edition. New York: McGraw Hill; 2009.

{{refend}}

{{Nervous system}}
{{Spinal nerves}}

{{Authority control}}

[[Category:Peripheral nervous system]]
[[Category:Spinal nerves|*]]