Posterior Compartment of the Thigh

Question 1

Biceps Femoris

Answer 1

Biceps Femoris
The biceps femoris has two heads (long head and short head) and is the most lateral of the muscles in the posterior thigh. The common tendon of the two heads can be felt laterally within the popliteal fossa (posterior knee region).

orgin:
The long head originates from the ischial tuberosity of the pelvis.
The short head originates from the linea aspera on posterior surface of the femur.
Together, the heads form a tendon, which inserts into the head of the fibula.

Actions: Main action is flexion at the knee. It also extends the thigh at the hip, and laterally rotates at the hip and knee.

Innervation:
Long head innervated by the tibial part of the sciatic nerve
The short head is innervated by the common fibular part of the sciatic nerve.

Question 2

Semimembranosus

Answer 2

The semimembranosus muscle is flattened and broad. It is located deep to the semitendinosus on the medial aspect of the posterior thigh.

Attachments: Originates from the ischial tuberosity (more superiorly than the origin of the semitendinosus and biceps femoris). Attaches to the medial tibial condyle.
Actions: Flexion of the leg at the knee joint. Extension of thigh at the hip. Medially rotates the thigh at the hip joint and the leg at the knee joint.
Innervation: Tibial part of the sciatic nerve.

Question 3

Semitendinosus

Answer 3

It Originates from the ischial tuberosity of the pelvis
It attaches to the medial surface of the tibia.
Actions: Flexion of the leg at the knee joint. Extension of thigh at the hip. Medially rotates the thigh at the hip joint and the leg at the knee joint.
Innervation: Tibial part of the sciatic nerve.