Spinal nerve

From Wikipedia, the free encyclopedia
  (Redirected from Coccygeal nerve)
Jump to: navigation, search
Spinal nerve
Spinal nerve.svg
The formation of the spinal nerve from the posterior and anterior roots
Details
Latin nervus spinalis
Identifiers
Gray's p.916
MeSH A08.800.800.720
Code TA A14.2.00.027
Anatomical terms of neuroanatomy

A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine.[1] 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.

Structure[edit]

Spinal nerve
Typical spinal nerve location

Each spinal nerve is formed from the combination of nerve fibers from its posterior and anterior roots. The posterior root is the afferent sensory root and carries sensory information to the brain. The anterior root is the 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 (the first vertebra). 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 lumbarized S1 vertebra (aka L6) or a sacralized L5 vertebra, the nerves are typically still counted to L5 and the next nerve is S1.

Scheme showing structure of a typical spinal nerve
1. Somatic efferent.
2. Somatic afferent.
3,4,5. Sympathetic efferent.
6,7. Sympathetic afferent

Outside the vertebral column, the nerve divides into branches. The posterior 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 anterior 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 (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 posterior 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. Major plexuses include the cervical, brachial, lumbar, and sacral plexuses.

Regional nerves[edit]

Cervical nerves[edit]

Cervical nerves

The cervical nerves are the spinal nerves from the cervical vertebrae. Although there are seven cervical vertebrae (C1-C7), there are eight cervical nerves C1C8. All cervical nerves except C8 emerge above their corresponding vertebrae, while the C8 nerve emerges below the C7 vertebra. Elsewhere 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, sternothyroid and omohyoid muscles.

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

Thoracic nerves[edit]

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 and trapezius 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 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[edit]

Further information: List of lumbar nerves
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 lateral branches 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 spine 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 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[edit]

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 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.[2][3]

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.[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 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.[5][6]

The sacral nerves have both 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 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.[7]

Coccygeal nerve[edit]

The coccygeal nerve is the 31st pair of spinal nerves. It arises from the sacral plexus, and its anterior root helps form the coccygeal plexus. It does not divide into a medial and lateral branch. It is distributed to the skin over the back of the coccyx.

Function[edit]

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 of the spinal nerves edit
Level Motor Function
C1-C6 Neck flexors
C1-T1 Neck extensors
C3, C4, C5 Supply diaphragm (mostly C4)
C5, C6 Shoulder movement, raise arm (deltoid); flexion of elbow (biceps); C6 externally rotates the arm (supinates)
C6, C7 Extends elbow and wrist (triceps and wrist extensors); pronates wrist
C7, T1 Flexes wrist; supply small muscles of the hand
T1 -T6 Intercostals and trunk above the waist
T7-L1 Abdominal muscles
L1, L2, L3, L4 Thigh flexion
L2, L3, L4 Thigh adduction; Extension of leg at the knee (quadriceps femoris)
L4, L5, S1 Thigh abduction; Flexion of leg at the knee (hamstrings); Dorsiflexion of foot (tibialis anterior); Extension of toes
L5, S1, S2 Extension of leg at the hip (gluteus maximus); Plantar flexion of foot and flexion of toes

Clinical significance[edit]

The muscles that one particular spinal root supplies are that nerve's myotome, and the 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.

Additional Images[edit]

References[edit]

  1. ^ "Spinal Nerves". National Library of Medicine. Retrieved 12 April 2014. 
  2. ^ 1. Anatomy, descriptive and surgical: Gray's anatomy. Gray, Henry. Philadelphia : Courage Books/Running Press, 1974
  3. ^ 2. Clinically Oriented Anatomy. Moore, Keith L. Philadelphia : Wolters Kluwer Health/Lippincott Williams & Wilkins, 2010 (6th ed)
  4. ^ 1. Anatomy, descriptive and surgical: Gray's anatomy. Gray, Henry. Philadelphia : Courage Books/Running Press, 1974
  5. ^ 1. Anatomy, descriptive and surgical: Gray's anatomy. Gray, Henry. Philadelphia : Courage Books/Running Press, 1974
  6. ^ 3. Human Neuroanatomy. Carpenter, Malcolm B. Baltimore : Williams & Wilkins Co., 1976 (7th ed)
  7. ^ 3. Human Neuroanatomy. Carpenter, Malcolm B. Baltimore : Williams & Wilkins Co., 1976 (7th ed)
  • 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.

External links[edit]