| Medical Dictionary: sem·i·mem·bra·no·sus muscle |
A muscle with origin from the tuberosity of the ischium, with insertion into the medial condyle of the tibia and by membrane to the tibial collateral ligament of the knee joint, the popliteal fascia, and the lateral condyle of the femur, with nerve supply from the tibial nerve, and whose action flexes the leg, rotates it medially, and makes the capsule of the knee joint tense.
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| Semimembranosus muscle | |
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| Muscles of the gluteal and posterior femoral regions. Semimembranosus labeled at bottom left. | |
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| Semimembranosus labeled at bottom right. | |
| Latin | musculus semimembranosus |
| Gray's | subject #128 479 |
| Origin | Ischial tuberosity |
| Insertion | Medial surface of tibia |
| Artery | profunda femoris, gluteal artery |
| Nerve | sciatic (tibial, L5, S1, S2) |
| Actions | Hip extension, Knee flexion |
| Antagonist | Quadriceps muscle |
The semimembranosus is a muscle in the back of the thigh. It is the most medial of the three hamstring muscles.
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The semimembranosus, so called from its membranous tendon of origin, is situated at the back and medial side of the thigh.
It arises by a thick tendon from the upper and outer impression on the tuberosity of the ischium, above and medial to the biceps femoris and semitendinosus.
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.
It is inserted mainly into the horizontal groove on the posterior medial aspect of the medial condyle of the tibia.
The tendon of insertion gives off certain fibrous expansions: one, of considerable size, passes upward and laterally to be inserted into the back part of the lateral condyle of the femur, forming part of the oblique popliteal ligament of the knee-joint; a second is continued downward to the fascia which covers the Popliteus muscle; while a few fibers join the tibial collateral ligament of the joint and the fascia of the leg.
The muscle overlaps the upper part of the popliteal vessels.
The semimembranosus is innervated by the tibial part of the sciatic nerve.
The semimembranosus helps to extend (straighten) the hip joint and flex (bend) the knee joint. It also helps medially rotate the knee.
It may be reduced or absent, or double, arising mainly from the sacrotuberous ligament and giving a slip to the femur or adductor magnus.
 Right hip bone. External surface. |
 Bones of the right leg. Posterior surface. |
 The popliteal, posterior tibial, and peroneal arteries. |
 Back of left lower extremity. |
This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated.
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 | Medial condyle of tibia |
| Medial collateral ligament |
| Popliteal fossa |
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 | Medical Dictionary. The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Read more |
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