Physiological unlocking is caused by -
Popliteus
Rectus femoris
Semimembranosus
Sartorius
During last stages of extension, femur rotates medially on tibia due to quadriceps femoris to lock the knee joint. Femur rotates laterally on tibia during flexion. 
Quadriceps femoris- Vastus medialis, vastus lateralis, vastus intermedius, rectus femoris. Unlocking occurs with popliteus.