Rectus femoris muscle

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Rectus femoris muscle
Rectus femoris.png
Muscles of the iliac and anterior femoral regions. (Rectus femoris visible near center.)
LatinMusculus rectus femoris
Gray'ssubject #128 470
Originanterior inferior iliac spine and the exterior surface of the bony ridge which forms the iliac portion of the acetabulum
Insertion   inserts into the patellar tendon as one of the four quadriceps muscles
Arterylateral femoral circumflex artery
Nervefemoral nerve
Actionsknee extension; hip flexion
AntagonistHamstring
 
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Rectus femoris muscle
Rectus femoris.png
Muscles of the iliac and anterior femoral regions. (Rectus femoris visible near center.)
LatinMusculus rectus femoris
Gray'ssubject #128 470
Originanterior inferior iliac spine and the exterior surface of the bony ridge which forms the iliac portion of the acetabulum
Insertion   inserts into the patellar tendon as one of the four quadriceps muscles
Arterylateral femoral circumflex artery
Nervefemoral nerve
Actionsknee extension; hip flexion
AntagonistHamstring

The rectus femoris muscle is one of the four quadriceps muscles of the human body. The others are the vastus medialis, the vastus intermedius (deep to the rectus femoris), and the vastus lateralis. All four parts of the quadriceps muscle attach to the patella (knee cap) via the quadriceps tendon.

The rectus femoris is situated in the middle of the front of the thigh; it is fusiform in shape, and its superficial fibers are arranged in a bipenniform manner, the deep fibers running straight down to the deep aponeurosis. Its function is to extend the knee by lifting the lower leg.[1]

Contents

Origin and insertion

It arises by two tendons: one, the anterior or straight, from the anterior inferior iliac spine; the other, the posterior or reflected, from a groove above the rim of the acetabulum.

The two unite at an acute angle, and spread into an aponeurosis which is prolonged downward on the anterior surface of the muscle, and from this the muscular fibers arise.

The muscle ends in a broad and thick aponeurosis which occupies the lower two-thirds of its posterior surface, and, gradually becoming narrowed into a flattened tendon, is inserted into the base of the patella.

The rectus femoris, sartorius and iliopsoas are the only muscles that are involved in flexion of the hip, since they are the only ones that originate in the pelvis and not the femur. By crossing the pelvic femoral joint they can act as a lever to flex the leg at the hip.

The rectus femoris is a weaker hip flexor when the knee is extended because it is already shortened and thus suffers from active insufficiency. In essence: the action of raising a straightened leg will recruit more iliacus, psoas major, tensor fasciae latae, and the remaining hip flexors than it will the rectus femoris.

Similarly, the rectus femoris is not dominant in knee extension when the hip is flexed since it is already shortened and thus suffers from active insufficiency. In essence: the action of extending a leg from a seated position is primarily driven by the vastus lateralis, vastus medialis, and vastus intermedius, and less by the rectus femoris.

In the other extreme, the muscle's ability to flex the hip and extend can be compromised in a position of full hip extension and knee flexion, due to passive insufficiency.

The rectus femoris is considered a direct antagonist to the hamstrings. The hamstrings oppose the rectus femoris at the hip joint through extension and at the knee joint through flexion. The rectus femoris can be torn which can be extremely painful and potentially debilitating if there is a complete rupture.

Motor Pathway

The neurons for voluntary upper leg contraction originate near the summit of the medial side of the precentral gyrus (the primary motor area of the brain). These neurons send a nerve signal that is carried by the corticospinal tract down the brainstem and spinal cord. The signal starts with the upper motor neurons carrying the signal from the precentral gyrus down through the internal capsule, through the cerebral peduncle, and into the medulla. In the medullary pyramid, the corticospinal tract decussates and becomes the lateral corticospinal tract. The nerve signal will continue down the lateral corticospinal tract until it reaches spinal nerve L4. At this point, the nerve signal will synapse from the upper motor neurons to the lower motor neurons. The signal will travel through the anterior root of L4 and into the anterior rami of the L4 nerve, leaving the spinal cord through the lumbar plexus. The posterior division of the L4 root is the Femoral nerve. The femoral nerve innervates the quadriceps femoris, a fourth of which is the rectus femoris. When the rectus femoris receives the signal that has traveled all the way from the medial side of the precentral gyrus, it contracts, extending the knee and flexing the thigh at the hip. (The information in above section is from the textbook, Anatomy and Physiology: The Unity of Form and Function, Saladin, 5th Ed)

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This article incorporates text from a public domain edition of Gray's Anatomy.