Summary Semimembranosus Origin Superior lateral quadrant of the ischial tuberosity Insertion Posterior surface of the medial tibial condyle Action Extends the thigh, flexes the knee, and also rotates the tibia medially, especially when the knee is flexed Innervation Tibial nerve (L5, S1, S2) Arterial Supply Perforating branches of profunda femoris artery, inferior gluteal artery, and the superior muscular branches of popliteal artery