Sciatic nerve

The sciatic nerve is a large nerve that runs down the lower limb. It is the longest 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 between 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 muscles of the foot.

Trivia

 * Sciatic nerves from frogs and rats are often used in physiology experiments on nerve conduction because this nerve is large, and easily dissected and manipulated.


 * In the Jewish dietary laws (Kashrut), the hindquarters of a mammal are not kosher unless the sciatic nerve and the fat surrounding it are removed (Genesis 32).

Pathology
Pain caused by a compressed or damaged sciatic nerve is called sciatica.