Notes Ch. 11f Nervous System II Anatomy and Physiology

Spinal Nerves There are 31 pairs of spinal nerves. They all originate from the spinal cord. They all provide 2 way communication between the spinal cord and parts of the upper and lower limbs, neck, and trunk. Spinal nerves are not named individually but they are grouped together.

There are 7 cervical vertebrae and 8 pairs of cervical nerves (numbered C1 to C8). There are 12 pairs of thoracic nerves (numbered T1 to T12). Five pairs of lumbar nerves (L1 to L5), and 5 pairs of sacral nerves (S1 to S5). One pair of coccygeal nerves (Co).

The ventral root of each spinal nerve is made of axons from the motor neurons whose cell bodies are in the gray matter of the cord. The dorsal root has dorsal root ganglion that has sensory neurons that move impulses inward to the spinal cord. These roots form a spinal nerve.

Plexuses are a network of ventral branches of spinal nerves Plexuses are a network of ventral branches of spinal nerves. In a plexus the fibers of different spinal nerves are sorted and recombined that allows the fibers that are part of a particular peripheral body part to reach its correct nerve.

Cervical Plexuses The cervical plexuses is the ventral branches of the first four cervical nerves, they are located deep in the neck on both sides. The 3rd, 4th, and 5th cervical nerves pass through the phrenic nerves which moves motor impulses to the diaphragm.

Brachial Plexuses The lower four cervical nerves and the first thoracic nerve form the brachial plexuses. These are in the shoulders between the neck and armpits. There are major branches in this plexuses: Musculocutaneous nerves - supply muscles of the arms and skin on the forearms.

2. Ulnar nerves - supply muscles of the forearms and hands and the skin of the hands. 3. Median nerves supply muscles of the forearm and muscles and skin of the hands. 4. Radial nerves supply muscles of the arms and skin of forearms and hands. 5. Axillary nerves supply muscles and skin of the anterior, lateral, and posterior regions of the arm.

There are other nerves associated with the brachial plexus that supplies nerves in muscles and skin of the chest and back.

Lumbosacral Plexuses The lumbosacral plexuses are made of the lumbar and first four sacral nerves. They provide motor and sensory nerves for the lower abdomen, genitalia, buttocks, thighs, legs, and feet.

The major nerves in this plexus are: The obturator nerves supply the adductor muscles in the thighs. The femoral nerves divide into many branches supplying motor impulses to muscles of the thighs and receiving impulses from the skin of the thighs and legs. 3. The sciatic nerves - the largest and longest nerves in the body. They move through the buttocks and into the thighs. They supply nerves to the muscles and skin of the thighs, legs, and feet.