Peripheral Nervous System -Part 3

 

Lumber plexus

It is formed by anterior rami of the 1^st 3 and part of lumber nerves. Situated in front of the transverse processes of the lumber vertebrae and behind the psoas muscle. The main branches and their nerve roots are,

            Iliohypogastric nerve: L1

            Ilioinguinal nerve: L1

            Genitofemoral: L1, L2

            Lateral cutaneous nerve of thigh: L2, L3

            Femoral nerve: L2, L3, L4

            Obturator nerve: L2, L3, L4

            Lumbosacral trunk: L4, L5

These nerves serve abdomen, back, groin, thighs, knees and calves

Iliohypogastric nerve, Ilioinguinal nerve, Genitofemoral – supply muscle and the skin in the area of the lower abdomen, upper and medial aspects of the thigh and the inguinal region. Lateral cutaneous nerve of thigh supplies the skin of the lateral aspect of the thigh including part of the anterior and posterior surfaces. Femoral nerve supplies the skin and the muscles of the front of the thigh. Obturator nerve supplies the adductor muscles of the thigh and skin of the medial aspect of the thigh. It ends just above the level of the knee joint.  Lumbosacral trunk descends into the pelvis and makes a contribution to the sacral plexus.

 

Sacral plexus

It is formed by the anterior rami of the lumbosacral trunk and the 1^st, 2^nd, and 3^rd sacral nerves. Serves the pelvis, buttocks, genitalia, thighs, calves and feet. Lumbosacral trunk is formed by the 5^th and part of the 4^th lumber nerves. It lies in the posterior wall of the pelvic cavity. Sacral plexus divides into a number of branches, supplying the muscles and skin of the pelvic floor, muscles around the hip joint and the pelvic organs. In addition to these, it provides the sciatic nerve, which contains fibers from L4 and 5 and S1 to S3. Sciatic nerve passes through the greater sciatic foramen into the buttock. Then descends through the posterior aspect of the thigh. It supplies the hamstring muscles. At the level of the middle of the femur, it divides to form the tibial and the common peroneal nerves. Tibial nerves descend through the popliteal fossa to the posterior aspect of the leg, to supply muscles and skin. It passes under the medial malleolus to supply muscles and skin of the sole of the foot and toes. Sural nerve supplies the tissues in the area of the heel, the lateral aspect of the ankle and a part of the dorsum of the foot. Peroneal nerve descends obliquely along the lateral aspect of the popliteal fossa, winds round the neck of the fibula into the front of the leg. It divides into the deep peroneal (arterial tibial) and the superficial peroneal (musculocutaneous) nerves. It supplies the skin and muscles of the anterior aspect of the leg and the dorsum of the foot and toes.  Perineal branch supplies the external anal sphincter, the external urethral sphincter and adjacent skin.

 

Coccygeal plexus

A very small plexus formed by part of the 4^th and 5^th sacral and the coccygeal nerves. Supply the skin around coccyx and anal area.

 

Thoracic nerves, do not intermingle to form plexuses. There are 12 pairs and first 11 are the intercostal nerves. They pass between the ribs supplying them, the intercostal muscles and overlying skin. The 12^th pair comprises the subcostal nerves. The 7^th to 12^th thoracic nerves also supply the muscles and the skin of the posterior and anterior abdominal walls.