Fig 1. Nerves and muscles of the upper leg. Gray's Anatomy.
Fig 2. Main branches of the femoral nerve.
The femoral nerve is one of the main nerves of the leg. The femoral nerve is made up of fibers from nerves in the second, third, and fourth segments of the lumbar spinal cord. The nerves emerge from the lower back region of the spine and run down into the thigh, where they branch to supply the skin and muscles of the front of the thigh (Fig 2). The nerve branches that supply the skin supply sensation from the front and inner side of the thigh; the branches that supply the muscles stimulate contraction of the quadriceps muscle at the front of the thigh, causing the knee to straighten.
Damage to the femoral nerve (which impairs the ability of the knee to straighten) is usually caused by a slipped disk in the lumbar region of the spine. Damage may also occur as the result of a backward dislocation of the hip or, rarely, as a result of neuropathy.