Semimembranosus (Hamstring)
Thigh · Lower Limb
The semimembranosus is a medial hamstring muscle lying deep to the semitendinosus, named for the broad, membranous tendon at its upper part. It arises from the ischial tuberosity and inserts on the posterior part of the medial condyle of the tibia. It flexes the knee, extends the hip, and medially rotates the flexed knee. It is supplied by the tibial division of the sciatic nerve (L5, S1, S2).
Origin, Insertion, Action & Nerve
Origin
Ischial tuberosity
Insertion
Posterior part of medial condyle of tibia
Action
Flexion of knee; extension of hip; medial rotation of flexed knee
Nerve
Tibial division of sciatic nerve (L5, S1, S2)
Attachments explained
The Semimembranosus (Hamstring) is defined first by where it attaches. Its origin is the more fixed anchor, usually the proximal or more stable end that stays put during contraction, while its insertion is the more mobile point that is pulled toward the origin when the muscle shortens.
Origin
Ischial tuberosity
Insertion
Posterior part of medial condyle of tibia
Action & function
When the Semimembranosus (Hamstring) contracts, it produces the following movements: Flexion of knee; extension of hip; medial rotation of flexed knee.
As part of the Thigh group of the Lower Limb, it works alongside neighbouring muscles to generate smooth, coordinated movement and to stabilise the structures it acts on.
Nerve supply & clinical relevance
The Semimembranosus (Hamstring) receives its nerve supply from the Tibial division of sciatic nerve (L5, S1, S2). This nerve carries fibres from spinal segment(s) L5, S1, S2.
Because a muscle can only contract when its nerve is intact, injury to the Tibial division of sciatic nerve or to its spinal roots (L5, S1, S2) can weaken or paralyse the Semimembranosus (Hamstring), impairing the movements it normally produces (flexion of knee). This is why knowing the innervation is central to localising nerve lesions in clinical practice.
How to study the Semimembranosus (Hamstring) (the OIANS method)
Learn the semimembranosus as the deep partner of semitendinosus, sharing the ischial tuberosity origin, the same three actions, and the same tibial-division supply. Distinguish it by its insertion onto the posterior medial condyle of the tibia rather than the pes anserinus, and by the flat, membranous upper tendon that gives it its name.
Keep it grouped with the other true hamstrings on the tibial division of the sciatic nerve (L5, S1, S2), and remember that, like semitendinosus, its medial insertion produces medial rotation of the flexed knee. Contrasting that with the lateral rotation of biceps femoris is the reliable way to separate the medial and lateral hamstrings.
Frequently asked questions
Where is the Semimembranosus (Hamstring) located?
The Semimembranosus (Hamstring) is a muscle of the Thigh group, located in the Lower Limb.
What is the origin of the Semimembranosus (Hamstring)?
Ischial tuberosity
What is the insertion of the Semimembranosus (Hamstring)?
Posterior part of medial condyle of tibia
What movements does the Semimembranosus (Hamstring) produce?
Flexion of knee; extension of hip; medial rotation of flexed knee
What nerve supplies the Semimembranosus (Hamstring)?
Tibial division of sciatic nerve (L5, S1, S2)
Is the Semimembranosus (Hamstring) free to study in OIANS?
The Semimembranosus (Hamstring) is always free to browse. Its full origin, insertion, action and nerve details are open to everyone in the Muscle Directory. Quiz and Flashcard practice for the Lower Limb is part of the one-time Lifetime upgrade, though; only the Upper Limb decks are free to test yourself on.
Related muscles
Study the Semimembranosus (Hamstring)
Test yourself on Lower Limb muscles with interactive quizzes and flashcards in the free OIANS app.
Quiz yourself → Flashcards Open the OIANS app
Browsing is always free. A one-time Lifetime unlock adds every region's quizzes, flashcards, progress tracking and explore tools.