The semimembranosus muscle () is the most medial of the three hamstring muscles in the thigh. It is so named because it has a flat tendon of origin. It lies posteromedially in the thigh, deep to the semitendinosus muscle. It extends the hip joint and

flexes Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

the knee joint.

Structure

The semimembranosus muscle, so called from its membranous tendon of origin, is situated at the back and medial side of the thigh. It is wider, flatter, and deeper than the semitendinosus (with which it shares very close insertion and attachment points). The muscle overlaps the upper part of the popliteal vessels.

Origin

The semimembranosus muscle originates by a thick tendon from the superolateral aspect of the ischial tuberosity. It arises above and medial to the biceps femoris muscle and semitendinosus muscle. The tendon of origin expands into an aponeurosis, which covers the upper part of the anterior surface of the muscle; from this aponeurosis, muscular fibers arise, and converge to another aponeurosis which covers the lower part of the posterior surface of the muscle and contracts into the tendon of insertion.

Insertion

The semimembranosus muscle inserts on the: * medial condyle of the

tibia The tibia (; ), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outside of the tibia); it conn ...

. * medial margin of the tibia. *

lateral condyle of femur The lateral condyle is one of the two projections on the lower extremity of the femur. The other one is the medial condyle. The lateral condyle is the more prominent and is broader both in its front-to-back and transverse diameters. Clinical sig ...

. * fascia of the

popliteus muscle The popliteus muscle in the leg is used for unlocking the knees when walking, by laterally rotating the femur on the tibia during the closed chain portion of the gait cycle (one with the foot in contact with the ground). In open chain movements ...

. The tendon of insertion gives off certain fibrous expansions: one, of considerable size, passes upward and laterally to be inserted into the posterior lateral condyle of the femur, forming part of the

oblique popliteal ligament The oblique popliteal ligament (posterior ligament) is a broad, flat, fibrous band on the posterior knee representing an expansion of the tendon of the semimembranosus muscle. It attaches onto the intercondylar fossa and lateral condyle of the fe ...

of the knee-joint; a second is continued downward to the fascia which covers the

; while a few fibers join the medial collateral ligament of the joint and the fascia of the leg.

Nerve supply

The semimembranosus is innervated by the tibial part of the sciatic nerve. The sciatic nerve consists of the anterior divisions of ventral nerve roots from L4 through S3. These nerve roots are part of the larger nerve network–the sacral plexus.Saladin, Kenneth S. Anatomy & Physiology: the unity of form and function. 5th ed. New York: McGraw-Hill, 2010. Print. The tibial part of the sciatic nerve is also responsible for innervation of semitendinosus and the long head of

biceps femoris The biceps femoris () is a muscle of the thigh located to the posterior, or back. As its name implies, it has two parts, one of which (the long head) forms part of the hamstrings muscle group. Structure It has two heads of origin: *the ''long ...

Variation

The semimembranosus muscle may be reduced or absent, or double, arising mainly from the sacrotuberous ligament and giving a slip to the femur or adductor magnus.

Function

The semimembranosus muscle extends (straightens) the hip joint. It also

(bends) the knee joint. It also helps to

medially rotate Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative ...

the knee: the

medially rotates on the

femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates ...

when the knee is flexed. It medially rotates the

when the hip is extended. The muscle can also aid in counteracting the forward bending at the hip joint.

Clinical significance

The semitendinosus muscle may be dry needled.

Additional images

Image:Gray235.png, Right hip bone. External surface. Image:Gray259.png, Bones of the right leg. Posterior surface. Image:Gray551.png, The popliteal, posterior tibial, and peroneal arteries. Image:Gray1239.png, Back of left lower extremity. Image:Femoral biceps muscle.jpg, Semimembranosus muscle File:Slide4j.JPG, Semimembranosus muscle File:Slide2DADE.JPG, Muscles of thigh. Lateral view. File:Slide2EA.JPG, Muscles of thigh. Cross section. File:Slide1BIBI.JPG, Muscles of thigh. Anterior views.

References

External links

* * - "Muscles (hamstrings) of the posterior compartment of the thigh." * - "Muscles that form the superficial boundaries of the popliteal fossa."
knee/surface/surface4
at the Dartmouth Medical School's Department of Anatomy
PTCentral
{{DEFAULTSORT:Semimembranosus Muscle Hip extensors Hip medial rotators Knee flexors Knee medial rotators Thigh muscles Posterior compartment of thigh Muscles of the lower limb Hamstring