15.3: Spinal Nerves
- Page ID
- 53740
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Above: Position and numbering of the cervical spinal nerves.
There are 31 pairs (right and left) of spinal nerves:
- 8 pairs of cervical spinal nerves
- 12 pairs of thoracic spinal nerves
- 5 pairs of lumbar spinal nerves
- 5 pairs of sacral spinal nerves
- 1 pair of coccygeal spinal nerves
All spinal nerves, except for the first pair and last six pairs, exit the vertebral column through intervertebral foramina. The first pair of spinal nerves (C1 spinal nerves) exit the vertebral column between the occipital bone and atlas (C1).
The ventral and dorsal rami of sacral nerves 1- 4 exit the vertebral column through the anterior and posterior sacral foramina respectively, and the 5th pair of sacral nerves and the one pair coccygeal nerves exits the vertebral column through the sacral hiatus
Above: Branches of spinal nerves. Blue represents sensory neurons and red represents motor neurons.
A plexus is a network of nerves. The three biggest nerve plexuses in the body are the cervical plexus (paired, right and left) which serves the head and neck, the brachial plexus (paired, right and left) which serves the upper limb, and the lumbosacral plexus (paired, right and left) which serves the pelvis, genitalia, and lower limb.
Above: Diagram numbering each spinal nerve (those with "n." after are the spinal nerves) and the nerve plexuses.
Cervical Plexus
The cervical plexus is a plexus of the ventral rami of the first four cervical spinal nerves (C1 through C4). They are located laterally to the transverse processes between prevertebral muscles from the medial side and vertebral from lateral side. There is anastomosis (cross-connection) with accessory nerve, hypoglossal nerve and sympathetic trunk.
It is located in the neck, deep to sternocleidomastoid. Nerves formed from the cervical plexus innervate the back of the head, as well as some neck muscles. The branches of the cervical plexus emerge from the posterior triangle at the nerve point, a point which lies midway on the posterior border of the sternocleidomastoid. Also from the dorsal ramus of C2 greater occipital nerve arises.
Above: Nerves of the cervical plexus shown with some of cranial nerves (C.N. IX glossopharyngeal nerve, C.N. X vagus nerve, and XII hypoglossal nerve).
The cervical plexus has two types of branches: cutaneous and muscular.
|
Nerve Name |
Nerves Involved |
Innervation |
|---|---|---|
|
Cutaneous branch |
||
|
greater auricular nerve |
ventral rami C2 and C3 spinal nerves |
Skin near the outer ear and external acoustic meatus (ear canal) |
|
lesser occipital nerve |
ventral rami of C2 spinal nerve |
Skin and the scalp posterosuperior to the outer ear |
|
supraclavicular nerves (lateral, intermediate, and medial) |
ventral rami C3 and C4 spinal nerves |
Skin below the clavicle |
|
transverse cervical nerve |
ventral rami C2 and C3 spinal nerves |
Anterior region of the neck |
|
Muscular branch |
||
|
ansa cervicalis nerve |
A loop formed from ventral rami of C1, C2, and C3 spinal nerves |
thyrohyoid, sternothyroid, sternohyoid, and omohyoid muscles |
|
phrenic nerve |
ventral rami of C3 through C5 spinal nerves |
Diaphragm, pericardium |
|
segmental branches |
ventral rami of C1 through C4 spinal nerves |
Anterior and middle scalenes muscles |
Brachial Plexus
Above: (Left) Diagram and (right) cadaver image of the right brachial plexus, anterior view
Above: Nerves of the upper limb (left) anterior left upper limb and (right) posterior right upper limb.
The brachial plexus is divided into roots, trunks, divisions, cords, and branches:
- roots: ventral roots of spinal nerves C5, C6, C7, C8, and T1
- trunks: superior, middle, and inferior trunks
- divisions: each of the superior, middle, and inferior trunks have an anterior division and a posterior division (6 divisions total)
- cords:
- lateral cord: the anterior divisions from the superior and middle trunks combine to form the lateral cord
- posterior cord: the posterior divisions from the superior, middle, and inferior trunks combine to form the posterior cord
- medial cord: comprised of the anterior division of the inferior trunk
- branches: musculocutaneous nerve, axillary nerve, radial nerve, median nerve, and ulnar nerve