|Insertion||Medial condyle of the tibia|
Extends the hip
Medially rotates tibia when knee is flexed
|Nerve||Tibial nerve of the sciatic plexus (L5, S1 and S2)|
|Artery||Profunda femoris and gluteal arteries|
Location & Overview
The semimembranosus muscle is a key muscle of the hamstring muscle group. This muscle is located in the posterior and medial aspects of the thigh. Among the three hamstring muscles (semimembranosus, biceps femoris, and semitendinosus) the semimembranosus muscle is the most medial. It primarily lies beneath the semitendinosus muscle and exhibits a flatter and wider shape in comparison .
The semimembranosus muscle originates from the ischial tuberosity, similar to the semitendinosus muscle, and both muscles share relatively close insertion points. These two muscles are located on the medial side of the thigh, while the biceps femoris muscle is situated on the lateral side. This positioning allows the semimembranosus to work in alongside the other hamstring muscles during movements of the lower limb .
Origin & Insertion
The semimembranosus muscle originates from the ischial tuberosity, which is a prominent bony landmark located at the base of the pelvis. This is the same origin point as the semitendinosus muscle, and both muscles are part of the hamstring muscle group  .
After originating from the ischial tuberosity, the semimembranosus muscle extends down the medial aspect of the thigh and eventually inserts onto the medial condyle of the tibia. The medial condyle of the tibia is a bony prominence situated on the inner side of the upper tibia, which is the larger of the two bones in the lower leg  .
The semimembranosus muscle contributes to several important movements of the lower limb. Its primary functions are flexing the knee joint, extending the hip joint, and medially rotating the knee joint when the knee is flexed  .
Flexion of the knee joint refers to bending the knee, this action brings the lower leg closer to the back of the thigh. In contrast, extension of the hip joint occurs when the thigh moves backwards in relation to the hip, as seen during walking or running  .
The semimembranosus muscle also contributes to the medial (inward) rotation of the knee joint (or tibia) when the knee is flexed. This action involves rotating the lower leg (tibia) inward relative to the thigh. This can be visualised by bending the knee and then turning the foot inward without moving the thigh  .
The semimembranosus muscle is innervated by the tibial division of the sciatic nerve, which is derived from the spinal levels of L5, S1, and S2. The sciatic nerve is the largest and longest nerve in the body. It originates from the lumbosacral plexus, which is a network of nerves located in the lower back region. The tibial division of the sciatic nerve travels down the posterior aspect of the thigh, providing motor innervation to the hamstring muscles, including the semimembranosus  .
The primary arteries supplying the semimembranosus muscle are the profunda femoris artery and the gluteal arteries. The profunda femoris artery (also known as the deep femoral artery) branches off the femoral artery and supplies blood to the muscles of the thigh, including the hamstring muscle group. The gluteal arteries, which consist of the superior and inferior gluteal arteries, arise from the internal iliac artery and contribute to the blood supply of the muscles in the gluteal and thigh regions, including the semimembranosus muscle  .
Want some flashcards to help you remember this information? Then click the link below:
Semimembranosus Muscle Flashcards
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|↑1, ↑2||Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017.|
|↑3, ↑5, ↑7, ↑9, ↑11, ↑14||Rodgers CD, Raja A. Anatomy, Bony Pelvis and Lower Limb, Hamstring Muscle. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK546688/|
|↑4, ↑6, ↑8, ↑10, ↑12||Afonso J, Rocha-Rodrigues S, Clemente FM, et al. The Hamstrings: Anatomic and Physiologic Variations and Their Potential Relationships With Injury Risk. Front Physiol. 2021;12:694604. Published 2021 Jul 7. doi:10.3389/fphys.2021.694604|
|↑13, ↑16||Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier.|
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