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Semimembranosus Muscle Anatomy

Quick Overview View Flashcards
Origin
  • Ischial tuberosity
Insertion
  • Medial condyle of the tibia
Action
  • Flexes the knee
  • Extends the hip
  • Medially rotates the tibia when the knee is flexed
Innervation
  • Tibial division of the sciatic nerve (L5, S1 and S2)
Blood Supply
  • Profunda femoris and gluteal arteries
Last updated: Estimated Reading Time: 8 min

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 has a flatter and wider shape by comparison.[1]

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 alongside the other hamstring muscles during movements of the lower limb.[1]

semimembranosus muscle from a posterior view
Here we can see the semimembranosus muscle from a posterior view.
semimembranosus muscle from a posterolateral view
Here we can see the semimembranosus muscle from a posterolateral view.
semimembranosus muscle from a lateral and medial view
On the left, we can see a lateral view of the semimembranosus muscle. On the right, we can see a medial view.
semimembranosus muscle highlighted in red from a posterior view
Here we can see the semimembranosus muscle highlighted in red among the other muscles of the leg. We can see a lateral view on the left and a medial view on the right. Muscles that are superficial to the semimembranosus have been removed to better show its location.
semimembranosus muscle highlighted in red from a posterior view
Here we can see the semimembranosus muscle highlighted in red, seen from a posterior view. Muscles that are superficial to the semimembranosus have been removed to better show its location.
Hamstring muscles labeled from a posterior view
Pictured here are the hamstring muscles from a posterior view. The long and short heads of biceps femoris, semitendinosus, and semimembranosus are labeled.
Compartments of the thigh
Here we can see an image of the compartments of the thigh. We can see the semimembranosus in the posterior compartment, the section colored in red.

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.[2,3]

Origin of the semimembranosus muscle marked in red
Pictured here is the origin of the semimembranosus muscle marked in red. It originates on the ischial tuberosity.

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.[2,3]

Distal tendon of the semimembranosus muscle
Pictured here is the distal tendon of the semimembranosus muscle where it inserts on the medial condyle of the tibia.
Insertion of the semimembranosus muscle marked in blue
Pictured here is the insertion of the semimembranosus muscle marked in blue on the medial condyle of the tibia.

Action & Function

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 tibia when the knee is flexed.[2,3]

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 backward in relation to the hip, as seen during walking or running.[2,3]

The semimembranosus muscle also contributes to medial (inward) rotation of the tibia when the knee is flexed. This action involves rotating the lower leg (tibia) inward relative to the thigh. This can be visualized as bending the knee and then turning the foot inward without moving the thigh.[2,3]

Image of a person demonstrating the movement of knee flexion.
In this image, you can see an example of knee flexion, which is the action of bending your knee. The opposite movement of knee flexion is knee extension. Knee flexion is an action of the semimembranosus muscle.
Image of a person demonstrating the movement of hip extension.
In this image, you can see an example of hip extension. Hip extension is the movement of the thigh or the upper leg backward, away from the body, in the sagittal plane. This action involves increasing the angle between the thigh and the pelvis, causing the hip joint to straighten or extend. The opposite movement of hip extension is hip flexion. Hip extension is an action of the semimembranosus muscle.
Image of a person demonstrating the movement of medial rotation of the tibia.
In this image, you can see an example of medial rotation of the tibia. Medial rotation of the tibia involves inward rotation of the shinbone toward the midline of the body. The opposite movement of medial rotation of the tibia is lateral rotation of the tibia. Medial rotation of the tibia is an action of the semimembranosus muscle, but only when the knee is flexed.

Innervation

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.[4,2]

sciatic nerve highlighted in red
Here we can see the sciatic nerve. Even though the tibial nerve separates from the sciatic nerve just above the knee, it is important to note that the nerves in our body are organized in a network, not in a strictly linear path. The nerve fibers that will eventually form the tibial nerve are present within the sciatic nerve from the point at which it leaves the spinal cord. These fibers travel within the sciatic nerve and reach the muscles they innervate, including the proximal (top) part of the semimembranosus muscle, long before the physical branching of the tibial nerve occurs near the knee. Thus, it is still accurate to say that the semimembranosus is innervated by the tibial nerve, even though the physical branching occurs distally.
tibial nerve highlighted in red
Here we can see the tibial nerve branching off from the sciatic nerve. The tibial division of the sciatic nerve innervates the semimembranosus muscle.

Blood Supply

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 from 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.[5,4]

References

  1. [1] Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincott Williams & Wilkins; 2017.
  2. [2] 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/
  3. [3] 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
  4. [4] Standring S. (2015). Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 41st Edn. Amsterdam: Elsevier.
  5. [5] Tomaszewski KA, Henry BM, Vikse J, Pękala P, Roy J, Svensen M, Guay D, Hsieh WC, Loukas M, Walocha JA. Variations in the origin of the deep femoral artery: A meta-analysis. Clin Anat. 2017 Jan;30(1):106-113. doi: 10.1002/ca.22691. Epub 2016 Feb 2. PMID: 26780216.

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