Sciatic nerve

Nervus ischiadicus

NervousNervesLegLeft and right

View left in 3D View right in 3D

What it is

The thickest and longest nerve in the body (L4-S3). It leaves the pelvis through the greater sciatic foramen below piriformis, curves down under gluteus maximus between the greater trochanter and the ischial tuberosity, and descends in the middle of the back of the thigh deep to the hamstrings, dividing above the knee into the tibial and common fibular nerves.

Function

Motor to the hamstrings and part of adductor magnus, and through its two divisions to every muscle below the knee; sensation from nearly all of the leg below the knee and the foot.

Size

Up to 2 cm wide at its origin; ~50 cm from the pelvis to the knee

Clinical note

Sciatica - pain shooting down the back of the leg - is usually caused by a disc pressing on its L5 or S1 root. Buttock injections go in the upper outer quadrant to avoid it.