spinal nerve

Information about spinal nerve

Nerve:
The formation of the spinal nerve from the dorsal and ventral roots
Scheme showing structure of a typical spinal nerve.
1. Somatic efferent.
2. Somatic afferent.
3,4,5. Sympathetic efferent.
6,7. Sympathetic afferent.
Latinnervi spinales
subject #208 916
MeSH Spinal+nerves
Dorlands/Elsevier n_05/12566663
The term spinal nerve generally refers to the mixed spinal nerve, which is formed from the dorsal and ventral roots that come out of the spinal cord. The spinal nerve is the bit that passes out of the vertebrae through the intervertebral foramen. All spinal nerves are part of the peripheral nervous system (PNS).

Numbering

There are a total of 31 bilaterally-paired spinal nerves : The first to seventh cervical nerves (C1 to C7) exit from the vertebral canal above the respective cervical vertebra(that is to say, C1 exits above the first cervical vertebra; C2 exits above the second, and so forth). The C8 spinal nerve exits below the seventh cervical vertebra, and all the other spinal nerves leave below their corresponding vertebra.

Formation of the spinal nerves

Inside the spinal cord, there is grey matter, surrounded by white matter. From out of the grey matter, two dorsal roots (one on the left side, and one on the right side) and two ventral roots emerge. (Dorsal means back, ventral means front.) As the body is symmetrical, the same thing happens on both the left and right side of the body. This happens in each vertebra of the spine.
  • The dorsal roots contain afferent sensory axons, and the ventral roots contain efferent motor axons. The dorsal roots of each side continue outwards, along the way forming a dorsal root ganglion (also called a spinal ganglion).
  • The ventral roots similarly continue out from the spinal column, and meet and mix with their corresponding dorsal nerve root at a point after the ganglion.
At this point, the combination of the dorsal roots and ventral roots is called a mixed spinal nerve.

Fate of the spinal nerve

After the dorsal and ventral roots fuse to form a spinal nerve, the nerve bifurcates into dorsal and ventral primary rami. Each primary ramus has two branches.

Dorsal

The two main branches are a lateral and medial branch.

Ventral

The two main branches are an anterior and lateral cutaneous branch. In addition, the anterior cutaneous bifurcates, forming a medial and lateral branch, while the lateral cutaneous branch splits into an anterior and posterior branch. These secondary and tertiary branches themselves typically have muscular and sensory branches that innervate the body wall.

The ventral primary rami also give rise to the roots of the various nervous plexuses (e.g. the brachial plexus), which become the sensory and motor nerves of the limbs.

Before forming the plexuses, the ventral rami have two branches leading to a sympathetic ganglion. These ganglia connect to the one above and below them, forming the sympathetic chain.

Importance of the spinal nerves

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.

This is of great importance in the diagnosis of neurological disorders, as lesions of one or more nerve roots result in typical patterns of neurologic defects (muscle weakness, loss of sensation) that allow localisation of the causating lesion.

Additional images


Cervical vertebra

A portion of the spinal cord, showing its right lateral surface. The dura is opened and arranged to show the nerve roots.

Distribution of cutaneous nerves. Ventral aspect.

Distribution of cutaneous nerves. Dorsal aspect.

The mechanism of the reflex arc


External links

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Nerves: spinal nerves
Cervicalanterior (Cervical plexus, Brachial plexus) - posterior (Posterior branches of cervical nerves, Suboccipital, Greater occipital, Third occipital)
Thoracicanterior (Intercostal, Intercostobrachial - T2, Thoraco-abdominal nerves - T7-T11, Subcostal - T12) - posterior (Posterior branches of thoracic nerves)
Lumbaranterior (Lumbar plexus, Lumbosacral trunk) - posterior (Posterior branches of the lumbar nerves, Superior cluneal nerves)
Sacralanterior (Sacral plexus) - posterior (Posterior branches of sacral nerves, Medial cluneal nerves)
Coccygealanterior (Coccygeal plexus) - posterior (Posterior branch of coccygeal nerve)
 •  • [ e]
Anatomy of torso (primarily): the spinal cord
Spinal nerveDorsal (Root, Ganglion, Ramus) • Ventral (Root, Ramus) • Sympathetic trunk • rami communicantes (Gray, White)
Gray matter/Rexed laminaePosterior horn (Column of Clarke, Substantia gelatinosa of Rolando, Nucleus proprius) • Lateral horn • Anterior horn • Central canal/Substantia gelatinosa centralis
White matter: somatic/ascending (blue)
White matter: motor/descending (red)
LayersEpidural space • Dura mater • Subdural space • Arachnoid mater • Subarachnoid space • Pia mater
Other structuresDenticulate ligaments • Conus medullaris • Cauda equina • Filum terminale • Cervical enlargement • Lumbar enlargement • Anterior median fissure
 •  • [ e]
Vertebral column and spinal cord
Vertebrae cervical: C1 (Atlas) • C2 (Axis) • C3 • C4 • C5 • C6 • C7 (Vertebra prominens) thoracic: T1 • T2 • T3 • T4 • T5 • T6 • T7 • T8 • T9 • T10 • T11 • T12 lumbar: L1 • L2 • L3 • L4 • L5 sacral: S1 • S2 • S3 • S4 • S5 coccygeal: Co1 • Co2 • Co3 • (Co4) • (Co5)
Spinal nerves cervical: C1 • C2 • C3 • C4 • C5 • C6 • C7 • C8 thoracic: T1 • T2 • T3 • T4 • T5 • T6 • T7 • T8 • T9 • T10 • T11 • T12 lumbar: L1 • L2 • L3 • L4 • L5 sacral: S1 • S2 • S3 • S4 • S5 coccygeal: Co
The somatic efferent neurons (GSE, 'somatomotor, or somatic motor fibers), arise from motor neuron cell bodies in the ventral horns of the gray matter within the spinal cord.
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The general somatic afferent fibers (GSA, or somatic sensory fibers), afferent fibers, arise from cells in the spinal ganglia and are found in all the spinal nerves, except occasionally the first cervical, and conduct impulses of pain, touch and temperature from the
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The general visceral efferent fibers (GVE or sympathetic efferent fibers), probably arise from cells in the lateral column or the base of the anterior column and emerge through the anterior roots and white rami communicantes.
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The general visceral afferent fibers (or sympathetic afferent fibers), conduct sensory impulses from the viscera through the rami communicantes and posterior roots to the spinal cord.
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Latin}}} 
Official status
Official language of: Vatican City
Used for official purposes, but not spoken in everyday speech
Regulated by: Opus Fundatum Latinitas
Roman Catholic Church
Language codes
ISO 639-1: la
ISO 639-2: lat
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Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed
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Elsevier, the world's largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. Based in Amsterdam, the company has substantial operations in the UK, USA and elsewhere.
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A nerve is an enclosed, cable-like bundle of axons (the long, slender projection of a neuron). Neurons are sometimes called nerve cells, though this term is technically imprecise since many neurons do not form nerves, and nerves also include the glial cells that
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spinal chord is a thin, tubular bundle of nerves that is an extension of the central nervous system from the brain and is enclosed in and protected by the bony vertebral column.
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The Vertebral Column (singular: vertebra) are the individual irregular bones that make up the spinal column (aka ischis) — a flexuous and flexible column.
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intervertebral foramina (singular: foramen; also called neural foramina). The foramen allows for the passage of the spinal nerve root, dorsal root ganglion, the spinal artery of the segmental artery, communicating veins between the internal and external plexuses,
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The Peripheral nervous system resides or extends outside the "CNS" central nervous system (the brain and spinal cord) to serve the limbs and organs. Unlike the central nervous system, however, the PNS is not protected by bone, leaving it exposed to toxins and mechanical injuries.
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The cervical nerves are the spinal nerves from the cervical vertebrae.

Although there are seven cervical vertebrae (C1-C7), there are eight cervical nerves (C1-C8).
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The thoracic nerves are the spinal nerves emerging from the thoracic vertebrae.

Anterior divisions

  • The intercostal nerves come from thoracic nerves T1-T11, and run between the ribs ("costae"). At T2 and T3, it further branches into the intercostobrachial nerve.

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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
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The five sacral nerves emerge from the sacrum. Although the vertebral components of the sacrum are fused into a single bone, the sacral vertebrae are still used to number the sacral nerves.
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The coccygeal nerve is the spinal nerve that corresponds to the coccyx bone.

Structure

The coccygeal nerve is the 31st spinal nerve. It arises from the sacral plexus, and its ventral ramus helps form the coccygeal plexus.
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In vertebrates, cervical vertebrae (singular: vertebra) are those vertebrae immediately behind (caudal to) the skull.

Variation among species

In some species, some parts of the skull may be composed of vertebra-like elements, e.g.
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In anatomy, the atlas (C1) is the topmost (first) cervical vertebra of the spine.

It is named for the Atlas of mythology, because it supports the globe of the head.
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Vertebra prominens is the proper name for the seventh cervical vertebra. The most distinctive characteristic of this vertebra is the existence of a long and prominent spinous process which is papable from the skin surface, hence the name.
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White matter is one of the three main solid components of the central nervous system designated by color. The other two are gray matter and substantia nigra.

Structure


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In anatomy and neurology, the dorsal root (or posterior root) is the afferent sensory root of a spinal nerve.

At the distal end of the dorsal root is the dorsal root ganglion, which contains the neuron cell bodies of the nerve fibres conveyed by the root.
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In anatomy and neurology, the ventral root (or anterior root) is the efferent motor root of a spinal nerve.

At its distal end, the ventral root joins with the dorsal root to form a mixed spinal nerve.
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afferent neurons--otherwise known as sensory or receptor neurons--carry nerve impulses from receptors or sense organs toward the central nervous system. This is the case vice versa as well. This term can also be used to describe relative connections between structures.
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Somatic sensation consists of the various sensory receptors that trigger the experiences labelled as touch or pressure, temperature (warm or cold), pain (including itch and tickle), and the sensations of muscle movement and joint position including posture, movement, and facial
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axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma.

Anatomy


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efferent nerves – otherwise known as motor or effector neurons – carry nerve impulses away from the central nervous system to effectors such as muscles or glands (and also the ciliated cells of the inner ear).
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Location Ventral horn of the spinal cord
Function Excitatory projection (to NMJ)
Neurotransmitter ACh
Morphology Projection neuron
Presynaptic connections M1 via the Corticospinal tract
Postsynaptic connections
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axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma.

Anatomy


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In anatomy and neurology, the dorsal root ganglion (or spinal ganglion) is a nodule on a dorsal root that contains cell bodies of neurons in afferent spinal nerves.

The axons of dorsal root ganglion neurons are known as afferents.
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