Spinal nerves


There are 31 pairs of spinal nerves, and the each is created by the unification of the anterior and posterior spinal root. This spinal root creeps from the spinal cord and then pushes through the intervertebral foramen on its way to innervate the body dermatome. There are distinctive categories for each of the pairs of spinal nerves. There are 8 cervical spinal nerves, 12 thoracic spinal nerves, 5 lumbar spinal nerves, 5 sacral spinal nerves, and 1 coccygeal spinal nerve. All the spinal nerves, (except the first cervical spinal nerve) traverse through the vertebral canal as well as the intervertebral foramina. The excepted first pair of cervical spinal nerves, finds its way through the opening between the occipital bone, which belongs to the skull, and the atlas.

For nerve pairs number 2 through seven, they simply exit just above the vertebrate for which they are aligned with. The eighth nerve pair, however, squeaks past the seventh cervical vertebrate and the first thoracic vertebrate. The pattern of coming forth just above the vertebrate for which they are named continued with the remaining pairs of spinal nerves.


The spinal nerve is anchored by the dorsal (posterior) root and the ventral (anterior) root. Each of these roots comprises either the motor (ventral) or the sensory (dorsal) fibers which create this mixed nerve. The dorsal root also contains the ganglion, which can be noted as an enlarged area along the beginnings of the root. The cell bodies which belong to the sensory neurons live within this ganglion. Sensory impulses relay the sensory related information via the dorsal root of the nerve fibers. The dendrites and other appropriate neurons then pick up the impulses in the spinal cord so synapse can occur.


Spinal nerves
Image: Spinal Nerves


The ventral root hosts the various axons which deal with motor neurons. These motor neurons are responsible driving command impulses away from the central nervous system. The eventual adjoining of the dorsal root and the ventral root leads to the actual creation of the spinal nerve, which then emerge together as a unit through the intervertebral foramen. However, once the unified nerve makes its way through the intervertebral foramen, it then branches off into various tributaries of itself. The meninges benefit as they receive their innervation from the small meningeal branch after it reenters the vertebral canal. It then continues to innervate the vertebrates and the vertebral ligaments.

The posterior ramus, which is a slightly larger branch of the original spinal nerve, innervates the skin, muscles, and joints associated with the back that runs along the vertebral column. Alternatively, the anterior ramus innervates the muscles of the anterior and lateral trunk, as well as the surrounding skin. Various combinations of anterior rami derived from various spinal nerves then innervate the limbs.

Two distinct branches from the spinal nerve which in turn make permanent contact with a sympathetic trunk ganglion are known as communicante ramis. They are also a vital part of the autonomic nervous system. Gray ramus, which means unmyelinated fibers, and the myelinated white fibers, create the rami communicantes.
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