Variations and anomalies of cranial and spinal nerves

The structure, branching paths, character and zones of branching of cranial and spinal nerves are very variable. The intertwining of nerve trunks, bundles in the formation of plexuses, the place of branches from the cranial and spinal nerves, from the plexus. The innervation of the muscles and the zone of branching of the skin nerves are also individually variable. Both cranial and spinal nerves can be traced along the location and extent of the connection of neighboring nerves with each other, and exchanges of bundles of nerve fibers are varied. Below are examples of variants and anomalies of nerves.

Significantly vary zones of sensitive innervation of the cranial nerves.

The large occipital nerve sometimes gives the ear branch to the skin of the auricle, and also the connecting branch with the small occipital nerve. This nerve can innervate the occipital abdomen of the cervical-frontal muscle.

The small occipital nerve may be absent or be doubled, replacing the missing large occipital nerve.

There may be additional diaphragmatic nerves that extend from the anterior branch III of the cervical spinal nerve, from the brachial plexus or from the subclavian nerve (most often). The diaphragmatic nerve in 38% of cases starts from the fourth cervical spinal nerve, in 16% from the fourth and fifth, in 22% from the third to fifth and in 19% of cases from the third and fourth cervical spinal nerves.

Two extreme forms of the structure of the brachial plexus are known . For the first, a broader arrangement of the branches and a large angle of their convergence are typical. A relatively narrow and short brachial plexus is typical for people with a narrow and long neck. The second form is typical for people with a short and wide neck: a close arrangement of the nerve branches of the plexus, which are connected at an acute angle to each other. The plexus itself is relatively wide and long.

The suprathiopathic nerve can innervate the middle or posterior staircase. The medial cutaneous nerve of the forearm sometimes delivers sensitive branches to the elbow joint. The musculocutaneous nerve is rarely absent, replaced by the branches of the median nerve. Often the musculocutaneous nerve gives branches to the elbow joint. The axillary nerve can be located in the thickness of the subscapular muscle, innervate it and the long head of the triceps muscle of the shoulder.

The median nerve often originates from the cervical spinal nerves.

The ulnar nerve is often formed from the anterior branches of the V-VIII spinal nerves.

The radial nerve is often formed by the fibers of the anterior branches of the lower cervical spinal nerves. In almost 50% of cases, the anatomical border of the area of the innervation of the rear of the hand does not correspond to the middle of the third finger, but shifts to one side.

The location of the lumbosacral plexus, its shape and dimensions are variable. The ilio-inguinal nerve may be absent. The femoral and genital branches of the femoral-genital nerve can depart directly from the lumbar plexus. From the middle part of the lumbar plexus, the anterior, medial and medial dermal nerves of the hip sometimes branch out . The lateral cutaneous nerve of the femur passes in 6% of cases together with the femoral nerve under the inguinal ligament. In 10% of cases there is an additional inhibitory nerve, passing near the medial edge of the large lumbar muscle.

Two extreme forms of fission of the femoral nerve are known :

1. The nerve is divided into a few, but large branches;
2. The nerve gives off a significant number of long and thin branches.

The femoral nerve can give the terminal branches above the level of the inguinal ligament.

The sciatic nerve sometimes perforates the pear-shaped muscle, it is often divided into the tibial and general peroneal nerves already in the cavity of the small pelvis or in the region of the large sciatic hole. The number and direction of the branches of the common peroneal nerve are variable. Sometimes the intermediate dorsal nerve of the foot ends at the rear of the foot, not reaching the fingers. The medial plantar nerve instead of the lateral plantar can give branches to the short muscle that folds the toes of the foot.

Age features of the peripheral nervous system

After birth, the number of neural bundles in the peripheral nerves increases: their branching becomes more complicated, the interconnection becomes more complicated, the receptor apparatuses become more complicated. With age, the thickness of nerve fibers increases. In elderly and senile age, the number of neurons in the spinal ganglia is reduced by 30%, part of the neurons atrophy.