Posterior compartment of thigh

Question 1

Semimembranosus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 1

• Origin - lateral part of ischial tuberosity.
• Insertion - medial condyle of tibia. Has 3 expansions from insertion.
• Nerve supply - tibial part of the sciatic nerve (L5, S1)
• Action - knee flexion, hip extension, IR of the knee when the knee is flexed.

Question 2

Semitendinosus:
* Origin
* Insertion
* Nerve supply
* Action

Answer 2

• Origin - arises in common with the long head of biceps, from the medial part of the ischial tuberosity.
• Insertion - inserts at the upper part of the medial surface of the tibia, behind the attachment of sartorius and infero-anterior to the attachment of gracilis (pes anserinus).
• Nerve supply - tibial part of the sciatic nerve (L5, S1)
• Action - knee flexion, hip extension, IR of the knee when the knee is flexed.

Question 3

Biceps femoris:
* Origin
* Insertion
* Nerve supply
* Action

Answer 3

• Origin - long head - arises in common with semitendinosus from the ischial tuberosity. Short head - linea aspera and lateral supracondylar line of the femur.
• Insertion - head of fibula.
• Nerve supply - long head - tibial component of the sciatic nerve (L5, S1).
  Short head - common peroneal (fibular) part of the sciatic nerve.
• Action - knee flexion, hip extension, ER of the knee when the knee is flexed.