The Hamstring muscles flex the knee. There are 3 of them
Semimembranosus: is the most superficial (closest to the surface), found on the medial (inner) side of the back of the thigh.
Semitendonosus: is found underneath semimembranosus
Biceps Femoris: is found on the lateral (outer) side of the back of the thigh. Attaches to the fibula and outside of the tibia
It plantar flexes the foot at the ankle and flexes the leg at the knee.
The knee
quadricep
rectus femoris
hamstrings
The Femoral nerve. (The motor branches innervate anterior thigh muscles - quadriceps, which flex the thigh and extend the knee.)
The gastrocnemius, the large muscle in the calf, flexes the knee and foot.
The hamstrings (specifically the long head of the biceps femoris, semitendonosis, and semimembranosis)
It is the rectus femoris, which along with the action of knee extension, it also flexes the hip
The Gastrocnemius and the Soleus flexes the knee and the foot. The Plantaris is an unimportant muscle. Many people do not have it and doctors tend to use this muscle for tendon graphs.
The sartorius flexes, abducts and laterally rotates the hip, and flexes and laterally rotates the knee The posterior fibers of the gluteus medius, laterally rotates the hip, while the whole glut medius works to abduct the hip
The knee joint is an example of a body joint that opens and closes as it flexes and extends during movement.