The sciatic nerve is the dominant nerve that innervates the lower back and the lower extremities. It travels from the lower spine, through the pelvis, and down each leg. It is the longest and widest nerve in the human body. The sciatic nerve primarily supplies the muscles of the lower leg, including the calf, ankle, and the back portion of the knee. It also supplies sensation to the sole of the foot, the ankle, the entire lower leg, and the back of the thigh.

The sciatic nerve branches into different parts of the body along its path, hence its ability to supply such a large area of the body. It is a mixed-function nerve, meaning that it contains both sensory neurons and motor neurons. This means that it simultaneously enables muscles to feel and to move.

Damage to the sciatic nerve can result in numerous symptoms, including lower back pain, muscle weakness and reflex abnormalities. Although it can be damaged anywhere, symptoms are usually present in the lower leg, such as an inability to bend the knee, shooting pain from the buttocks to the lower leg, or difficulty in rotating and bending the foot.