Muscles - Posterior Thigh

Question 1

Give an overview of the posterior thigh, including:

location
structure
function
muscles

Answer 1

Location:
the posterior thigh muscles are located between the posterior and lateral intermuscular septum and the fascia lata, on the posterior aspect of the thigh. They span between the ischial tuberosities of the pelvis and the superior tibia and fibula, with only the short head of the biceps femoris originating from the posterior surface of the femur rather than the ischium.

Structure:
The muscles of the posterior thigh are long, strong muscles. The true hamstring muscles are the long head of the biceps femoris, the semimembranosus and the semitendinosus, which span between the ischial tuberosities and the superior tibia and fibula. These muscles cross both the hip and knee joint. The short head of the biceps femoris crosses only the knee joint and as such is not a true hamstring muscle.

Function:
The three true hamstring muscles are responsible for extension of the thigh and flexion of the knee, while the short head of the biceps femoris contributes to knee flexion only.

In addition the semimembranosus and semitendinosus muscles contribute to internal rotation of the thigh when the knee is flexed and can extend the trunk when the leg is fixed, and the biceps femoris contribute to external rotation of the thigh when the knee is flexed.

Muscles:
There are 3 muscles in the posterior thigh:

biceps femoris (short and long head)
semimembranosus
semitendinosus

Question 2

Which nerves innervate the posterior thigh muscles?

Answer 2

The tibial part of the sciatic nerve innervates all muscles except the short head of the biceps femoris, which is innervated by the fibular part of the sciatic nerve.

Question 3

Give an overview of the muscles of the posterior thigh:

Answer 3

Biceps femoris:
PA: long head: ischial tuberosity; short head: linea aspera and lateral supracondylar line of the femur
DA: lateral side of the fibular head
NS: long head: tibial portion of sciatic nerve, short head: fibular portion of sciatic nerve
A: long head: extends thigh; both heads: flexes knee, externally rotates leg when knee is flexed

Semimembranosus:
PA: ischial tuberosity
DA: medial tibial condyle (posterior aspect) and oblique popliteal ligament
NS: tibial part of sciatic nerve
A: extends thigh, flexes knee, internally rotates leg when knee is flexed, and extends trunk when leg is fixed

Semitendinosus:
PA: ischial tuberosity
DA: medial tibia (pes anserine)
NS: tibial part of sciatic nerve
A: extends thigh, flexes knee, internally rotates leg when knee is flexed, and extends trunk when leg is fixed