Antagonist Quadriceps muscle | ||
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Origin tuberosity of the ischium, linea aspera, femur Insertion the head of the fibula which articulates with the back of the lateral tibial condyle Artery deep femoral artery, perforating arteries; long head of biceps femoris: perforating branches from profunda femoris artery Nerve long head: tibial nerve
short head: common fibular nerve Actions flexes knee joint, laterally rotates knee joint (when knee is flexed), extends hip joint (long head only) | ||
The biceps femoris (/ˈbaɪsɛps ˈfɛmərᵻs/) is a muscle of the thigh located to the posterior, or back. As its name implies, it has two parts, one of which (the long head) forms part of the hamstrings muscle group.
Contents
Structure
It has two heads of origin;
The fibers of the long head form a fusiform belly, which passes obliquely downward and lateralward across the sciatic nerve to end in an aponeurosis which covers the posterior surface of the muscle, and receives the fibers of the short head; this aponeurosis becomes gradually contracted into a tendon, which is inserted into the lateral side of the head of the fibula, and by a small slip into the lateral condyle of the tibia.
At its insertion the tendon divides into two portions, which embrace the fibular collateral ligament of the knee-joint.
From the posterior border of the tendon a thin expansion is given off to the fascia of the leg. The tendon of insertion of this muscle forms the lateral hamstring; the common fibular (peroneal) nerve descends along its medial border.
Variations
The short head may be absent; additional heads may arise from the ischial tuberosity, the linea aspera, the medial supracondylar ridge of the femur, or from various other parts. The tendon of insertion may be attached to the Iliotibial band and to retinacular fibers of the lateral joint capsule.
A slip may pass to the gastrocnemius.
Innervation
It is a composite muscle as the short head of the biceps femoris develops in the flexor compartment of the thigh and is thus innervated by common fibular branch of the sciatic nerve (L5, S2), while the long head is innervated by the tibial branch of the sciatic nerve (L5, S2).
Blood supply
The muscle's vascular supply is derived from the anastomoses of several arteries: the perforating branches of the profunda femoris artery, the inferior gluteal artery, and the popliteal artery.
Function
Both heads of the biceps femoris perform knee flexion.
Since the long head originates in the pelvis it is also involved in hip extension. The long head of the biceps femoris is a weaker knee flexor when the hip is extended (because of active insufficiency). For the same reason the long head is a weaker hip extender when the knee is flexed.
When the knee is semi-flexed, the biceps femoris in consequence of its oblique direction rotates the leg slightly outward.
Clinical significance
Avulsion of the biceps femoris tendon is common in sports that require explosive bending of the knee as seen in sprinting.