Muscles Acting on the Hip and Femur
Muscles Acting on the Knee and Leg
Some muscles that act on the femur cross both the hip and knee joints to act on the leg. Other muscles are recognized as more exclusively affecting knee motions. The body's most powerful muscle, the quadriceps femoris, is a tensor muscle that plays the primary role in extending the knee. A tensor muscle is a muscle that stretches or tightens a part of the body. In the knee, this mechanism of action is critical to running, kicking, and standing up. Located in the thigh's anterior or extensor compartment, the quadriceps femoris has four heads: the rectus femoris, the vastus lateralis, the vastus medialis, and the vastus intermedius. These meet and connect to the knee's patella through the quadriceps (patellar) tendon. The connection continues as the patellar ligament, which inserts on the tibial tuberosity. The patellar ligament is the structure physicians tap with a reflex hammer in order to test the knee-jerk reflex. The sartorius muscle, also in the thigh's anterior compartment, is the body's longest. The strap-like muscle crosses over the quadriceps, arranged between the hip's lateral side and knee's medial side. The sartorius enables crossing the legs by laterally rotating the thigh and flexing the hip and knee.The group of muscles known as the hamstrings are contained in the thigh's posterior or flexor compartment. These three muscles—the biceps femoris, the semimembranosus, and the semitendinosus—flex the knee. Together with the gluteus maximus, they also contribute to walking and running by extending the hip. All the hamstrings originate at the ischial tuberosity; a second head of the biceps femoris originates at the femur's posterior midshaft. The biceps femoris inserts at the head of the fibula, the semimembranosus at the tibia's medial condyle, and the semitendinosus near the tibial tuberosity. Injuries to the hamstring are common in many athletes. The femoral nerve innervates muscles acting on the knee that are situated in the thigh's anterior compartment. Hamstring muscles, which are in the posterior compartment, are innervated primarily by the tibial nerve.
Muscles of the Knee
Muscles Acting on the Foot
Intrinsic muscles of the foot are those not arising elsewhere. These layered muscles aid locomotion by collectively extending, flexing, abducting, and adducting the toes and supporting the arch of the foot. They bear similarities in name and action to muscles of the hand. The extensor digitorum brevis, which extends the toes, is the only intrinsic foot muscle on the foot's dorsal (upper) side. The remaining muscles are found on the foot's ventral side (bottom) or between the metatarsal bones. These are categorized into four layers, from top to bottom. The first, or most superficial, layer includes the flexor digitorum brevis, which is connected by tendons to all the digits except the hallux (large toe). It is flanked by muscles connected by tendons to the little and large toe, respectively—the abductor digiti minimi and the abductor hallucis. The quadratus plantae muscle, which flexes the toes, and the four lumbrical muscles make up the second layer. The lumbricals flex metatarsophalangeal joints and extend interphalangeal joints. Deeper still, the third layer includes the adductor hallucis, which adducts the hallux or big toe, the flexor digiti minimi brevis, and the flexor hallucis brevis. The latter two muscles flex the little toe and big toe, respectively. The plantar aponeurosis, a broad, fan-shaped tissue between the plantar skin and muscles, is the point of origin for many muscles in the first three layers. The fourth and deepest layer comprises seven muscles. Four dorsal interosseous muscles abduct toes 2 to 5, and three plantar interosseous muscles adduct toes 3 to 5. Innervation of the foot's intrinsic muscles is achieved primarily by the medial and lateral plantar nerves.