| Spinal nerve | |
|---|---|
 The formation of the spinal nerve from the posterior and anterior roots | |
| Details | |
| Identifiers | |
| Latin | nervus spinalis |
| MeSH | D013127 |
| TA98 | A14.2.00.027 |
| TA2 | 6143 |
| FMA | 5858 |
| Anatomical terms of neuroanatomy | |
Aspinal nerve is amixed nerve, which carriesmotor,sensory, andautonomic signals between thespinal cord and the body. In thehuman body there are 31 pairs of spinalnerves, one on each side of thevertebral column.[1][2] These are grouped into the correspondingcervical,thoracic,lumbar,sacral andcoccygeal regions of the spine.[1] There are eight pairs ofcervical nerves, twelve pairs ofthoracic nerves, five pairs oflumbar nerves, five pairs ofsacral nerves, and one pair ofcoccygeal nerves. The spinal nerves are part of theperipheral nervous system.[1]
Each spinal nerve is amixed nerve, formed from the combination ofnerve rootfibers from itsdorsal andventral roots. The dorsal root is theafferent sensory root and carries sensory information to the brain. The ventral root is theefferent 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 theoccipital bone and theatlas (the first vertebra).[3] 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 alumbarized S1 vertebra (also known as L6) or asacralized L5 vertebra, the nerves are typically still counted to L5 and the next nerve is S1.
Outside the vertebral column, the nerve divides into branches. Thedorsal 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). Theventral 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. Themeningeal 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. Therami 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 anerve 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. Thespinal plexuses are thecervical plexus,brachial plexus,lumbar plexus, thesacral plexus and the much smallercoccygeal plexus.[3]
The cervical nerves are the spinal nerves from the cervical vertebrae in thecervical segment of the spinal cord. Although there are seven cervical vertebrae (C1–C7), there are eight cervical nervesC1–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 thesuboccipital nerve (C1), thegreater occipital nerve (C2) and thethird occipital nerve (C3). The anterior distribution includes thecervical plexus (C1–C4) andbrachial plexus (C5–T1).
The cervical nerves innervate thesternohyoid,sternothyroid andomohyoid muscles.
A loop of nerves calledansa cervicalis is part of the cervical plexus.
The thoracic nerves are the twelve spinal nerves emerging from the thoracic vertebrae. Each thoracic nerve T1–T12 originates from below each correspondingthoracic vertebra. Branches also exit the spine and go directly to theparavertebral ganglia of theautonomic nervous system where they are involved in the functions of organs and glands in the head, neck, thorax and abdomen.
Theintercostal nerves come from thoracic nerves T1–T11, and run between the ribs. At T2 and T3, further branches form theintercostobrachial nerve. Thesubcostal nerve comes from nerve T12, and runs below the twelfth rib.
The medial branches (ramus medialis) of the posterior branches of the upper six thoracic nerves run between thesemispinalis dorsi andmultifidus, which they supply; they then pierce therhomboid andtrapezius muscles, 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 andlongissimus dorsi, occasionally they give off filaments to the skin near the middle line. This sensitive branch is called the posterior cutaneous ramus.
Thelumbar nerves are the five spinal nerves emerging from the lumbar vertebrae. They are divided into posterior and anterior divisions.
The medial branches of the posterior divisions of the lumbar nerves run close to the articular processes of the vertebrae and end in themultifidus muscle.
The laterals supply theerector spinae muscles.
The upper three give off cutaneous nerves which pierce the aponeurosis of thelatissimus dorsi at the lateral border of the erector spinae muscles, and descend across the posterior part of theiliac crest to the skin of thebuttock, some of their twigs running as far as the level of thegreater trochanter.
The anterior divisions of the lumbar nerves (rami anteriores) increase in size from above downward. They are joined, near their origins, bygray rami communicantes from thelumbar ganglia of thesympathetic trunk. These rami consist of long, slender branches which accompany thelumbar arteries around the sides of the vertebral bodies, beneath thepsoas major. Their arrangement is somewhat irregular: one ganglion may give rami to two lumbar nerves, or one lumbar nerve may receive rami from twoganglia.
The first and second, and sometimes the third and fourth lumbar nerves are each connected with the lumbar part of the sympathetic trunk by awhite ramus communicans.
The nerves pass obliquely outward behind the psoas major, or between itsfasciculi, distributing filaments to it and thequadratus lumborum.
The first three and the greater part of the fourth are connected together in this situation by anastomotic loops, and form thelumbar plexus.
The smaller part of the fourth joins with the fifth to form thelumbosacral trunk, which assists in the formation of thesacral plexus. The fourth nerve is named thefurcal nerve, from the fact that it is subdivided between the two plexuses.
Thesacral nerves are the five pairs of spinal nerves which exit thesacrum at the lower end of thevertebral column. The roots of these nerves begin inside the vertebral column at the level of theL1 vertebra, where thecauda equina begins, and then descend into the sacrum.[4][5]
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 theanterior sacral foramina and the other division through theposterior sacral foramina.[4]
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 thesacral plexus and thelumbosacral plexus. The branches of these plexus give rise to nerves that supply much of thehip,thigh,leg andfoot.[4][6]
The sacral nerves have bothafferent andefferent fibers, thus they are responsible for part of thesensory 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 thedescending colon andrectum,urinary bladder andgenital 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 thecentral nervous system (CNS) and motor impulses from the CNS to the pelvis that control the movements of these pelvic organs.[6]
The bilateral coccygeal nerves, Co, are the 31st pair of spinal nerves. It arises from the conus medullaris, and its ventral ramus helps form thecoccygeal plexus. It does not divide into a medial and lateral branch. Its fibers are distributed to the skin superficial and posterior to thecoccyx bone via theanococcygeal nerve of the coccygeal nerve plexus.
| Level | Motor function |
|---|---|
| C1–C6 | Neckflexors |
| C1–T1 | Neckextensors |
| C3,C4,C5 | Supplydiaphragm (mostlyC4) |
| C5,C6 | Moveshoulder, raisearm (deltoid); flex elbow (biceps) |
| C6 | externally rotate (supinate) the arm |
| C6,C7 | Extendelbow andwrist (triceps and wristextensors);pronate wrist |
| C7,C8 | Flex wrist; supply small muscles of thehand |
| T1–T6 | Intercostals andtrunk above thewaist |
| T7–L1 | Abdominal muscles |
| L1–L4 | Flexhip joint |
| L2,L3,L4 | Adduct thigh; Extendleg at theknee (quadriceps femoris) |
| L4,L5,S1 | abduct thigh; Flex leg at the knee (hamstrings);Dorsiflexfoot (tibialis anterior); Extendtoes |
| L5,S1,S2 | Extend leg at thehip (gluteus maximus); flex foot and flex toes |
Aspinal plexus is a weblikenerve plexus formed by theanterior nerve roots that branch andmerge repeatedly. The only region that does not have a plexus is the thoracic region. The smallcervical plexus is in the neck, thebrachial plexus is in the shoulder, thelumbar plexus is in the lower back, beneath this is thesacral plexus, and next to the lower sacrum andcoccyx is the very smallcoccygeal plexus.[3]
The muscles that one particular spinal root supplies are that nerve'smyotome, and thedermatomes 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 insacral 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
