What Nerves Affect the Quad Muscle?

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Runners legs (Image: OcusFocus/iStock/Getty Images)

The quadriceps femoris, or quad muscle, is located at the front of the thigh and is responsible for straightening the leg from a bent position. As indicated by its name, it is actually composed of four muscles: the rectus femoris, vastus medialis, vastus lateralis and vastus intermedialis. These four muscles all converge to end in the patellar ligament and attach to an area of the shinbone called the tibial tuberosity.

Spinal Nerve Roots

The peripheral nervous system consists of all the nerves outside of the brain and spinal cord. Peripheral nerves exit from the spinal column through openings in the vertebral canal called foramina. The lower back is known as the lumbar region of the spine. A series of nerves that emerge between the vertebrae of the lumbar spine carry nerve impulses that will ultimately serve the motor functions of the quadriceps femoris. According to the University of Michigan Medical School, these are the second through fourth lumbar nerves, designated L2 through L4, and they form a network known as the lumbar plexus.

The Femoral Nerve

The femoral nerve is formed by the combined nerve fibers of the L2, L3 and L4 nerves, which converge after exiting the vertebral canal. This nerve passes down the front of the pelvis, under the inguinal ligament of the hip, and adjacent to the femoral artery. In addition to supplying sensory nerve function to the inner surface of the leg, the femoral nerve branches off to supply motor impulses to the four heads of the quadriceps femoris.

Quadriceps Nerve Dysfunction

When the femoral nerve is damaged, paralysis and sensory deficits can affect the leg. The University of Maryland Medical Center explains that damage to the femoral nerve can result from direct injury, nerve compression, nerve entrapment, systemic disorders, tumors, infections or internal bleeding. Compression of the femoral nerve can also occur as a complication of surgery that involves lying on the back with the hips and knees bent.

Because the femoral nerve passes through some relatively narrow anatomical structures, it is vulnerable to damage from compression or entrapment. Even something as seemingly benign as an overly tight belt can cause compression of the femoral nerve. Prolonged periods of pressure placed upon the femoral nerve can restrict blood flow and prevent oxygen from reaching the nerve tissue, leading to nerve damage.

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