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In human anatomy, the sacral plexus is a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg and foot, and part of the pelvis. It is part of the lumbosacral plexus and emerges from the lumbar vertebrae and sacral vertebrae (L4-S4). [ 1 ]
English: An (admittedly extremely rough) schematic of the sacral plexus based on "Netter, Frank (2011) Atlas of Human Anatomy, Saunders Elsevier, pp. 487 ISBN: 978-1-4160-5951-6. " or equivalently the reproduction at this site.
This plexus lies within the psoas major muscle. Nervi of the plexus serve the skin and the muscles of the lower abdominal wall, the thigh and external genitals. The largest nerve of the plexus is the femoral nerve. It supplies anterior muscles of the thigh and a part of skin distal to the inguinal ligament.
The anterior divisions of the lumbar nerves, sacral nerves, and coccygeal nerve form the lumbosacral plexus, the first lumbar nerve being frequently joined by a branch from the twelfth thoracic. For descriptive purposes this plexus is usually divided into three parts: lumbar plexus; sacral plexus; pudendal plexus
The lumbosacral trunk from the L4 and L5 roots descends between the sacral promontory and ala, and the S1 to S3 roots emerge from the ventral sacral foramina. These nerve roots unite to form a single nerve in front of the piriformis muscle. The nerve passes beneath the piriformis and through the greater sciatic foramen, exiting the pelvis.
Diagram of sacral plexus and pudendal plexus. (Label "to piriformis" is at center left.) ... is the peripheral nerve that provides motor innervation to the piriformis ...
S1 supplies many muscles, either directly or through nerves originating from S1. They are not innervated with S1 as single origin, but partly by S1 and partly by other spinal nerves. The muscles are: gluteus maximus muscle; gluteus medius muscle; gluteus minimus muscle; tensor fasciae latae; piriformis; obturator internus muscle; inferior gemellus
Its branches are all cutaneous, and are distributed to the gluteal region, the perineum, and the back of the thigh and leg. The inferior clunial nerves (or gluteal branches), three or four in number, turn upward around the lower border of the gluteus maximus, and supply the skin covering the lower and lateral part of that muscle.