Semimembranosus muscle
Muscles of the gluteal and posterior femoral regions. Semimembranosus labeled at bottom left.
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.

Contents 1 Structure 2 Innervation 3 Actions 4 Variations 5 Additional images 6 See also 7 External links

[edit] Structure

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.

[edit] Innervation

The semimembranosus is innervated by the tibial part of the sciatic nerve.

[edit] Actions

The semimembranosus helps to extend (straighten) the hip joint and flex (bend) the knee joint. It also helps medially rotate the knee.

[edit] Variations

It may be reduced or absent, or double, arising mainly from the sacrotuberous ligament and giving a slip to the femur or adductor magnus.

[edit] Additional images

Right hip bone. External surface.

Bones of the right leg. Posterior surface.

The popliteal, posterior tibial, and peroneal arteries.

Back of left lower extremity.

[edit] See also

• Semitendinosus
• Biceps femoris

[edit] External links

• LUC semm
• SUNY Labs 14:st-0408
• SUNY Figs 14:01-07 - "Muscles (hamstrings) of the posterior compartment of the thigh."
• SUNY Figs 14:02-06 - "Muscles that form the superficial boundaries of the popliteal fossa."
• Anatomy at Dartmouth knee/surface/surface4
• PTCentral

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained within it may be outdated.

v • d • e List of muscles of lower limbs (TA A04.7, GA 4.465) ILIAC Region / ILIOPSOAS psoas major/psoas minor · iliacus BUTTOCKS gluteals: (maximus, medius, minimus) · tensor fasciae latae lateral rotator group: quadratus femoris · inferior gemellus · obturator internus · superior gemellus · piriformis THIGH / compartments Anterior sartorius · quadriceps (rectus femoris, vastus lateralis, vastus intermedius, vastus medialis) · articularis genu Posterior/hamstring biceps femoris · semitendinosus · semimembranosus Medial pectineus · obturator externus · gracilis · adductor (longus, brevis, magnus) Fascia Femoral sheath (Femoral canal) · Femoral ring Adductor canal · Adductor hiatus fascia lata (Iliotibial tract, Lateral intermuscular septum of thigh, Medial intermuscular septum of thigh, Fascia cribrosa/Saphenous opening) LEG/ Crus/ compartments Anterior tibialis anterior · extensor hallucis longus · extensor digitorum longus · peroneus tertius Posterior superficial · triceps surae (gastrocnemius, soleus, Achilles tendon) · plantaris deep · tarsal tunnel (flexor hallucis longus, flexor digitorum longus, tibialis posterior) · popliteus Lateral peroneus muscles (longus, brevis) Fascia Pes anserinus crural fascia (Anterior crural intermuscular septum, Posterior crural intermuscular septum, Transverse intermuscular septum) FOOT Dorsal extensor hallucis brevis · extensor digitorum brevis Plantar 1st layer (abductor hallucis, flexor digitorum brevis, abductor digiti minimi) · 2nd layer (quadratus plantae, lumbrical muscle) · 3rd layer (flexor hallucis brevis, adductor hallucis, flexor digiti minimi brevis) · 4th layer (dorsal interossei, plantar interossei) Fascia Plantar fascia retinacula (Peroneal, Inferior extensor, Superior extensor, Flexor)