Spinal nerve | Neurology | Anjani Mishra

  Written by Anjani Mishra

Spinal nerve

How spinal nerve is formed ?

• Spinal nerve is formed by the dorsal nerve root and ventral nerve root, because each spinal nerve is attached to the spinal cord by two roots, a ventral or motor root and a dorsal or sensory root.

• The dorsal root is larger and more massive than the ventral root because of the large number of rootlets, arises from the dorsal horn of the gray matter of the spinal cord. It is sensory which carry information from periphery to the brain.

• The ventral root is smaller and less massive than the dorsal root, arises from the ventral horn of the gray matter of the spinal cord. It is motor which carry information from brain to the periphery.

• The dorsal and ventral root unite immediately beyond the spinal ganglion to form the spinal nerve which emerges through the intervertebral foramen. The spinal ganglion is located on the dorsal root of the spinal nerve and is usually placed near or in the intervertebral foramen immediately outside the dura matter.

• The dorsal branches of the spinal nerve after they have emerged, are smaller, as a rule, than the ventral division. There are certain cervical and caudal(coccygeal) exceptions.

• The dorsal branches are usually divided into medial and lateral branches to supply the muscles and skin of the dorsal part of the neck and trunk.

• The ventral branches of the spinal nerves are larger than the dorsal divisions. They supply the ventral and lateral parts of the trunk and all parts of the limbs. 

Brachial and lumbosacral plexus

Brachial Plexus

The brachial plexus is formed by the ventral branches of the last three cervical and first two thoracic spinal nerves in the bovine and equine ( only the first thoracic in the sheep and goat).

It appears as a thick, wide band between the dorsal and ventral scalenus muscle and supply mainly the muscles of the forelimb.

The following table showing the nerves derived from the brachial plexus and the muscles supplied by each are as follows;

 

S.No.	Name of the nerve	Supply/distribution
1	The large supra-scapular nerve	Supaspinatus & infraspinatus muscles
2	The much smaller subscapular nerve	Subscapularis muscle
3	The pectoral nerve/anterior thoracic nerve	Superficial & deep pectorals muscles
4	The musculocutaneous nerve	Biceps brachii, brachialis and coracobrachialis muscles
5	The median nerve	Flexor carpi radialis, deep digital flexor and pronator teres muscles
6	The ulnar nerve	Flexor carpi ulnaris, superficial and deep digital flexor and many intrinsic muscles of the digit
7	The radial nerve	Triceps brachii(medial, lateral & long head), extensor carpi radialis, common lateral and medial digital extensor, extensor carpi ulnaris and adductor muscles
8	The axillary nerve	Teres major, teres minor, deltoideus and brachiocephalicus muscles
9	The long thoracic nerve	Serratus ventralis muscle
10	The thoracodorsal nerve	Latissimus dorsi muscle
11	The lateral thoracic nerve	Cutaneous trunci muscle and skin of the abdominal wall

Lumbosacral plexus

The lumbosacral plexus is formed by the ventral branches of the last three lumbar and first two sacral spinal nerves (both in ruminants and horse).

The following nerves derived from the lumbosacral plexus and the muscles supplied by them are as follows;

 

S.No.	Name of the nerve	Supply/distribution
1	The cranial gluteal nerve	Middle and deep gluteus muscles and tensor fascia latae muscle
2	The caudal gluteal nerve	Superficial gluteus muscle
3	The femoral nerve	Quadriceps femoris Sartorius, rectus femoris, pectineus, vastus lateralis, medialis & intermedius, psoas major and iliacus muscles
4	The obturator nerve	Adductor, gracilis and obturator externus muscles
5	The ischiatic nerve	Semitendinosus, semimembranosus, biceps femoris, obturator internus, gemelli and quadratus femoris muscles
6	The tibial nerve	Gastrocnemius, popliteus, superficial and deepdigital flexor, and tibial posterioris muscles
7	The peroneal nerve	Tibialis anterior, long and medial extensor, lateral digital extensor, peroneus longus and peroneus tertius muscles

Fig: Lumbosacral plexus

Autonomic nervous system

S.No.	Differential points	Sympathetic N.S.	Parasympathetic N.S.
1	Anatomical entity	Present definite anatomical entity   Accompanies thoracic and lumbar spinal nerves   Thoraco-lumbar outflow   Pre-ganglionic fibers are shorter than the post ganglionic fibers   Post-ganglionic fibers are longer than the pre-ganglionic fibers One pre-ganglionic neuron synapses with about 20 post-ganglionic neurons	Present no anatomical entity   Accompanies certain cranial and sacral spinal nerves   Cranio-sacral outflow   Pre-ganglionic fibers are longer than the post ganglionic fibers   Post-ganglionic fibers are shorterer than the pre-ganglionic fibers One pre-ganglionic neuron synapses with few post-ganglionic neurons
2	Action	Produce mass action   Convey mostly visceral pain   It is a nerve of emergency and works during stress	Produce localized and isolated effects   Convey general visceral pain   It is nerve for tranquility and maintains well sustained vegetative state
3	On stimulation	Heart rate is accelerated, Blood pressure is raised, Pupil dilated, intestinal peristalsis is diminished and the sphincter of the gut are closed, Liberates non-adrenalin at the post-ganglionic endings	Heart rate is slowed, Blood pressure is fallen, Pupil constricted, Intestinal peristalsis is enhanced, Liberates acetyl-choline at the post-ganglionic endings
4	Central control	Posterior part of hypothalamus for sympathetic activity	Anterior part of hypothalamus for parasympathetic activity

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