Introduction of spinal nerve:-
- Cervical spinal nerves
- Thoracic spinal nerves
- Lumbar spinal nerves
- Sacral spinal nerves
Cervical spinal nerve:-
There are eight pairs of cervical spinal nerves.
The first of these emerges through the intervertebral foramen of atlas, the second through the border of the arch of the axis and the eighth between the seventh cervical and the first dorsal vertebrae.
First cervical
The dorsal branch supplies the anterior oblique and the dorsal straight muscles of the head and skin.
The ventral branch passes out through the alar foramen of atlas, runs across the rectus capitis ventralis major divides near the thyroid gland into anterior and posterior branches.
The former to supplies the omohyoideus and the latter joins a branch of the second cervical to supply the sternothyrohyoideus.
Second cervical
The dorsal branch supplies the muscles and the skin of the occipital region.
The ventral branch supplies the rectus capitis ventralis major, sternothyrohyoideus and anastomotic branches to the spinal accessory nerve and ventral divisions of first and third cervical nerves.
It also supplies a posterior auricular branch to skin on the convex face of external ear and a cutaneous branch to the parotid region.
Third cervical
Its dorsal branch supplies the intertransversales colli, multifidus cervicis and complexus.
The ventral branch supplies the longus colli, rectus capitis ventralis major, brachiocephalicus, splenius and longissimus capitis et atlantis.
Fourth cervical
Similar to the preceding.
Fifth cervical
Similar to the preceding.
In addition to supplying the lateral cervical group of muscles it gives a branch to the brachial plexus and another branch to form one of the roots of the phrenic nerve.
Sixth cervical
Similar to the preceding. In addition to supplying the lateral cervical group of muscles it gives a branch to the brachial plexus and another branch to form one of the roots of the phrenic nerve.
Seventh cervical
The dorsal branch is small and supplies the longissimus dorsi and multifidus dorsi.
The ventral branch gives off a fine branch that forms one of the roots of phrenic nerve and then goes to form the brachial plexus.
Eighth cervical
The dorsal branch is small and is like that of the seventh.
The ventral branch contributes to form the brachial plexus.
Thoracic spinal nerve:-
There are thirteen pairs of dorsal spinal nerves and their arrangements are almost similar.
The dorsal branches pass up into the intertransverse space and divide into medial and lateral branches of which the former supply the spinal muscles and skin of the region.
The lateral branches are directed upward, pass through the longissimus dorsi and appear between it and the transversalis costarum. They break off into filaments to supply the skin.
The ventral branches are the intercostal nerves. The first and second dorsal enter into the formation of the brachial plexus.
The ventral branches of the rest are much larger than the dorsal branches and descend into the intercostal spaces in company with the vessels.
At the upper half they run in between the intercostal muscles and supplies it.
About the middle they comes out of the muscle as perforating branch supply the cutaneous muscle and skin of the thorax and abdomen.
The intercostal nerves from the eighth to the thirteenth supply sensory branches to the diaphragm.
Lumbar spinal nerve:-
There are six pairs of nerves. The dorsal branches are distributed to the muscles, situated above the transverse processes of the lumbar vertebrae and supplies the skin of the loin. The ventral branches slightly differ in their distribution.
They pass under the psoas minor and psoas major and emerge at the lateral border of the latter. They supply branches to the sublumbar muscles, abdominal muscles and the skin.
The ventral branch of the first lumber is termed ilio-hypogastric nerve, which divides into a superficial cutaneous branch and a deep muscular branch.
The superficial branch passes downward and backward between the internal and external oblique muscles, perforating the latter, supplies skin on the posterior part of the flank and lateral aspect of the thigh.
The deep branch runs under the peritoneum and supplies internal oblique and rectus abdominis muscles.
The ventral branch of the second lumbar supplies psoas major and continues as the ilio-inguinal nerve.
This also divides into a superficial branch supplying skin in front of thigh and lateral face of the stifle.
The deep branch supplies abdominal muscles, unites with a branch from the third lumbar nerve passes through the inguinal canal, supplies external genitalia and skin of inguinal region.
The ventral branch of the third lumbar gives branches to psoas muscles and divides into superficial and deep branches.
The superficial branch continues as the lateral cutaneous nerve of the thigh, passes outward and backward, emerges below the point of hip, between iliacus and obliques abdominis externus, under the cover of tensor fasciae latae and supplies the skin of the stifle region.
The deep branch forms the external spermatic nerve which descends into the inguinal region.
The ventral branches of the fourth, fifth and sixth lumbar spinal nerves enter into the formation of the lumbo-sacral plexus.
Sacral spinal nerve:-
The dorsal branches are small, gain exit through the dorsal sacral foramina and supply the muscles and skin of the croup.
The ventral branches of the first and second enter into the formation of the lumbo-sacral plexus.
The third generally gives off a branch to the plexus and the rest unites with the fourth and divides into pudic and posterior haemorrhoidal nerves.
The pudic nerve passes on the sacrosciatic ligament, gives off branches to the bladder, urethra and muscular branches to the muscles of the anus.
At the ischial arch it supplies branches to ischiocavernosus, urethra, and corpus cavernosum penis in the male and vulva in the female and terminate in the clitoris.
The pudic nerve in the male is continued around the ischial arch, descends on the dorsum penis to reach the glans penis. It supplies the erectile tissue and prepuce.
The posterior haemorrhoidal nerve supplies the rectum.
The ventral primary branch of the fifth is small and supplies the muscles of the anus and skin, compressor coccygeus and skin of the tail.
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