Cervical nerves The cervical nerves are the spinal nerves from the cervical vertebrae in the
cervical segment of the spinal cord. Although there are seven cervical vertebrae (C1–C7), there are eight cervical nerves
C1–
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,
sternothyroid and
omohyoid muscles. 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 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 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
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 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. 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: 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 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.
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 ==