Sciatic nerve

Sciatic nerve

The sciatic nerve (also known as the ischiatic nerve) is a large nerve that starts in the lower back and runs through the buttock and down the lower limb. It is the longest and widest single nerve in the body.

The sciatic supplies nearly the whole of the skin of the leg, the muscles of the back of the thigh, and those of the leg and foot.

Anatomical course

The nerve enters the lower limb by exiting the pelvis through the greater sciatic foramen, below the Piriformis muscle.

It descends midway in the greater trochanter of the femur and the tuberosity of the ischium, and along the back of the thigh to about its lower third, where it divides into two large branches, the tibial and common peroneal nerves. This division may take place at any point between the sacral plexus and the lower third of the thigh. When it occurs at the plexus, the common peroneal nerve usually pierces the Piriformis muscles.

In the upper part of its course, the nerve rests upon the posterior surface of the ischium, the nerve to the Quadratus femoris, the Obturator internus and Gemelli; it is accompanied by the posterior femoral cutaneous nerve and the inferior gluteal artery, and is covered by the Gluteus maximus.

Lower down, it lies upon the Adductor magnus, and is crossed obliquely by the long head of the Biceps femoris.

Branches

The nerve gives off articular and muscular branches.

  • The articular branches (rami articulares) arise from the upper part of the nerve and supply the hip-joint, perforating the posterior part of its capsule; they are sometimes derived from the sacral plexus.
  • The muscular branches (rami musculares) are distributed to the following muscles of the lower limb: Biceps femoris, Semitendinosus, Semimembranosus, and Adductor magnus. The nerve to the short head of the Biceps femoris comes from the common peroneal part of the sciatic, while the other muscular branches arise from the tibial portion, as may be seen in those cases where there is a high division of the sciatic nerve.

The muscular branch eventually gives off the tibial nerve and common peroneal nerve, which innervates the muscles of the (lower) leg. The tibial nerve goes on to innervate all muscles of the foot except the extensor digitorum brevis (peroneal nerve).

Pathology

Pain caused by a compression or irritation of the sciatic nerve by a problem in the lower back is called sciatica. Common causes of sciatica include the following low back conditions: spinal disc herniation, degenerative disc disease, spinal stenosis, and spondylolisthesis.

In religion

In the Jewish religion, consumption of the sciatic nerve is forbidden, even from otherwise kosher and properly slaughtered animals. This traditionally traces back to the Biblical account of Jacob being wounded when wrestling with the angel. The sciatic nerve is known in Hebrew as gid hanasheh. The process of removing the sciatic nerve (as well as certain large blood vessels and forbidden fats) from the surrounding meat is known as nikkur, or "deveining." Since this is a difficult and delicate process, cuts from an animal's hindquarters are generally not sold as kosher.

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