The semimembranosus muscle () is the most medial of the three

hamstring A hamstring () is any one of the three posterior thigh muscles in human anatomy between the hip and the knee: from medial to lateral, the semimembranosus, semitendinosus and biceps femoris. Etymology The word " ham" is derived from the Old ...

muscles in the

thigh In anatomy, the thigh is the area between the hip (pelvis) and the knee. Anatomically, it is part of the lower limb. The single bone in the thigh is called the femur. This bone is very thick and strong (due to the high proportion of bone tissu ...

. It is so named because it has a flat tendon of origin. It lies posteromedially in the thigh, deep to the

semitendinosus muscle The semitendinosus () is a long superficial muscle in the Posterior compartment of thigh, back of the thigh. It is so named because it has a very long tendon of insertion. It lies posteromedially in the thigh, superficial to the semimembranosus. ...

. It extends the

hip joint In vertebrate anatomy, the hip, or coxaLatin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) (: ''coxae'') in medical terminology, refers to either an anatomical region or a joint o ...

and flexes the

knee joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the ...

Structure

The semimembranosus muscle, so called from its membranous tendon of origin, is situated at the back and medial side of the

. 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 The ischial tuberosity (or tuberosity of the ischium, tuber ischiadicum), also known colloquially as the sit bones or sitz bones, or as a pair the sitting bones, is a large posterior bony protuberance on the superior ramus of the ischium. It ...

. It arises above and medial to the biceps femoris muscle and

. The tendon of origin expands into an

aponeurosis An aponeurosis (; : aponeuroses) is a flattened tendon by which muscle attaches to bone or fascia. Aponeuroses exhibit an ordered arrangement of collagen fibres, thus attaining high tensile strength in a particular direction while being vulnerable ...

, 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 (; : tibiae or tibias), also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two Leg bones, bones in the leg below the knee in vertebrates (the other being the fibula, behind and to the outsi ...

. * 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 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 of the

knee-joint In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). It is the largest joint in the hu ...

; a second is continued downward to the fascia which covers the popliteus muscle; while a few fibers join the

medial collateral ligament The medial collateral ligament (MCL), also called the superficial medial collateral ligament (sMCL) or tibial collateral ligament (TCL), is one of the major ligaments of the knee. It is on the medial (inner) side of the knee joint and occurs in ...

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, also called the ischiadic nerve, is a large nerve in humans and other vertebrate animals. It is the largest branch of the sacral plexus and runs alongside the hip joint and down the right lower limb. It is the longest and widest ...

. 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 In human anatomy, the sacral plexus is a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg and foot, and part of the pelvis. It is part of the lumbosacral plexus and emerges from the lumbar verteb ...

.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 The semitendinosus () is a long superficial muscle in the back of the thigh. It is so named because it has a very long tendon of insertion. It lies posteromedially in the thigh, superficial to the semimembranosus. Structure The 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 consists of two heads; the long head is considered part of the hamstring muscle group, while the short head is sometimes excluded from this ...

Variation

The semimembranosus muscle may be reduced or absent, or double, arising mainly from the

sacrotuberous ligament The sacrotuberous ligament (great or posterior sacrosciatic ligament) is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends. Structure It runs from the sacrum (the lowe ...

and giving a slip to the femur or

adductor magnus The adductor magnus is a large triangular muscle, situated on the medial side of the thigh. It consists of two parts. The portion which arises from the ischiopubic ramus (a small part of the inferior ramus of the pubis, and the inferior ramu ...

Function

The semimembranosus muscle extends (straightens) the

. It also flexes (bends) the

. It also helps to medially rotate the knee: the

medially rotates on the

femur The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg. The Femo ...

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

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

." * - "Muscles that form the superficial boundaries of the

popliteal fossa The popliteal fossa (also referred to as hough or kneepit in analogy to the cubital fossa) is a shallow depression located at the back of the knee joint. The bones of the popliteal fossa are the femur and the tibia. Like other flexion surfaces ...

."
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