Human Leg - Anatomy - Neurovascular System - Nerves

Nerves

The sensory and motor innervation to the lower limb is supplied by the lumbosacral plexus, which is formed by the ventral rami of the lumbar and sacral spinal nerves with additional contributions from the subcostal nerve (T12) and coccygeal nerve (Co1). Based on distribution and topography, the lumbosacral plexus is subdivided into the lumbar plexus (T12-L4) and the Sacral plexus (L5-S4); the latter is often further subdivided into the sciatic and pudendal plexuses:

The lumbar plexus is formed lateral to the intervertebral foramina by the ventral rami of the first four lumbar spinal nerves (L1-L4), which all pass through psoas major. The larger branches of the plexus exit the muscle to pass sharply downward to reach the abdominal wall and the thigh (under the inguinal ligament); with the exception of the obturator nerve which pass through the lesser pelvis to reach the medial part of the thigh through the obturator foramen. The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior part of the thigh. The iliohypogastric (T12-L1) and ilioinguinal nerves (L1) emerge out of the psoas major near the muscle's origin, from where they run laterally downward to pass anteriorly above the iliac crest between the transversus abdominis and abdominal internal oblique, and then run above the inguinal ligament. Both nerves give off muscular branches to both these muscles. Iliohypogastric supplies sensory branches to the skin of the lateral hip region, and its terminal branch finally pierces the aponeurosis of the abdominal external oblique above the inguinal ring to supply sensory branches to the skin there. Ilioinguinalis exits through the inguinal ring and supplies sensory branches to the skin above the pubic symphysis and the lateral portion of the scrotum. The genitofemoral nerve (L1, L2) leaves psoas major below the two former nerves, immediately divides into two branches that descends along the muscle's anterior side. The sensory femoral branch supplies the skin below the inguinal ligament, while the mixed genital branch supplies the skin and muscles around the sex organ. The lateral femoral cutaneous nerve (L2, L3) leaves psoas major laterally below the previous nerve, runs obliquely and laterally downward above the iliacus, exits the pelvic area near the iliac spine, and supplies the skin of the anterior thigh. The obturator nerve (L2-L4) passes medially behind psoas major to exit the pelvis through the obturator canal, after which it gives off branches to obturator externus and divides into two branches passing behind and in front of adductor brevis to supply motor innervation to all the other adductor muscles. The anterior branch also supplies sensory nerves to the skin on a small area on the distal medial aspect of the thigh. The femoral nerve (L2-L4) is the largest and longest of the nerves of the lumbar plexus. It supplies motor innervation to iliopsoas, pectineus, sartorius, and quadriceps; and sensory branches to the anterior thigh, medial lower leg, and posterior foot.

The nerves of the sacral plexus pass behind the hip joint to innervate the posterior part of the thigh, most of the lower leg, and the foot. The superior (L4-S1) and inferior gluteal nerves (L5-S2) innervate the gluteus muscles and the tensor fascia latae. The posterior femoral cutaneous nerve (S1-S3) contributes sensory branches to the skin on the posterior thigh. The sciatic nerve (L4-S3), the largest and longest nerve in the human body, leaves the pelvis through the greater sciatic foramen. In the posterior thigh if first gives off branches to the short head of the biceps femoris and then divides into the tibial (L4-S3) and common fibular nerves (L4-S2). The fibular nerve continues down on the medial side of biceps femoris, winds around the fibular neck and enters the front of the lower leg. There it divides into a deep and a superficial terminal branch. The superficial branch supplies the peroneus muscles and the deep branch enters the extensor compartment; both branches reaches into the dorsal foot. In the thigh, the tibial nerve gives off branches to semitendinosus, semimembranosus, adductor magnus, and the long head of the biceps femoris. The nerve then runs straight down the back of the leg, through the popliteal fossa to supply the ankle flexors on the back of the lower leg and then continues down to supply all the muscles in the sole of the foot. The pudendal (S2-S4) and coccygeal nerves (S5-Co2) supply the muscles of the pelvic floor and the surrounding skin.

The picture on the top shows a woman's legs and the below picture a young male's legs in long shorts

The lumbosacral trunk is a communicating branch passing between the sacral and lumbar plexuses containing ventral fibers from L4. The coccygeal nerve, the last spinal nerve, emerges from the sacral hiatus, unites with the ventral rami of the two last sacral nerves, and forms the coccygeal plexus.

See also: Cutaneous innervation of the lower limbs

Read more about this topic:  Human Leg, Anatomy, Neurovascular System

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