Muscles - Anatomy

The brachialis only produces motion across one joint; it flexes the elbow. The biceps brachii flex the shoulder and elbow and supinate the forearm. The triceps brachii extends both the shoulder and elbow. The extensor carpi radialis longus produces motion across the elbow and the wrist.

The sartorius originates from the anterior superior iliac spine (ASIS) and inserts near the tibial tuberocity, running laterally to medially along the anterior thigh. Because the sartorius crosses both the hip and the knee, contraction of the muscle is capable of flexing both the leg and thigh. By running laterally to medially, shortening of the muscle also causes lateral rotation and abduction of the thigh.

The quadriceps muscle group is primarily responsible for the extension of the knee. This group includes the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius. The biceps femoris part of the hamstring muscle group and is responsible for the flexion of the knee.

The semitendinosus, gracilis, and sartorius are the three muscles that make up the pes anserine group, coming from the posterior, medial, and anterior compartments of the thigh, respectively. The adductor longus, is not part of this group as it inserts on the linea aspera of the femur, rather than the pes anserinus, like the semitendinosus, gracilis, and sartorius.

No muscles attach to the talus directly. However, the extensor digitorum brevis comes close, via its attachment to one of the talocalcaneal ligaments.

The achilles tendon or calcaneal tendon inserts on the posterior side of the calcaneus. It is the largest tendon in the body and pulls the heel up to point the toes downward. This decreases the angle between the bottom of the foot and back of the leg. This is called plantar flexion.

The soleus is the correct answer. The gastrocnemius also inserts on the calcaneus, but it originates on the condyles of the femur. Th plantaris muscle also inserts at the calcaneus, but it also originates at the femur. The biceps femoris muscles are located on the posterior side of the thigh. The sartorius originates on the anterior superior iliac spine, and inserts on the anteromedial aspect of the tibia.

We are looking for a muscle in the posterior compartment of the thigh. This means that the muscle will be on the back of the leg, between the pelvis and the kneecap. The correct answer is the gracilis muscle, which unlike the other three is located in the anterior compartment of the thigh.

The transversospinal group is made up of the multifidi, the semispinalis group, and the rotatores group. The overall action of these muscles is extension and rotation of the vertebral column. The quadratus lumborum muscle laterally flexes the vertebral column, and, when bilaterally contracted, depresses the rib cage.

The iliofemoral ligament connects the ilium to the femur and is taut in end range hip extension (as in doing front splits) and external rotation.

The flexor hallucis longus attaches to the plantar surface of the hallux or big toe. Much of the spring force (originating in the foot) when walking or running is generated by the contraction of this muscle. The popliteus and gastrocnemius muscles are in the crural region. The flexor digitorum longus is also in the foot, but acts to flex the second, third, fourth, and fifth toes which generate less push force.

The fibularis (peroneus) longus depresses the base of the first metatarsal, allowing the body to advance forward, over the limb that is in contact with the ground (the stance limb).

The quadriceps muscle group consists of four different regions, each with a different origin. The rectus femoris originates on the anterior inferior iliac spine (AIIS). The vastus lateralis originates from the greater trochanter of the femur. The vastus medialis originates from the intertrochanteric line. The vastus intermedius originates from the shaft of the femur. Together, the muscles of the quadriceps work to extend the leg by straightening the knee.

The biceps femoris is located posterior to the femur, and is a part of the hamstring muscle group. The primary action of the biceps femoris is flexion of the leg by bending the knee.

Plantar flexion involves increasing the angle between the foot and the leg (pointing the toe). The gastrocnemius is found on the posterior portion of the leg, and is contracted in order to cause plantar flexion of the foot. The other muscle to contribute to this action is the soleus, also located in the posterior portion of the leg.

The tibialis anterior is located in the anterior portion of the leg and is involved in dorsiflexion, the opposite of plantar flexion. The biceps femoris and rectus femoris are located in the thigh, and do not act on the position of the foot. The biceps femoris is involved in flexion of the knee and the rectus femoris is involved in extension of the knee.

The gluteus maximus is innervated by the inferior gluteal nerve. The gluteus medius and minimus are innervated by the superior gluteal nerve. The femoral nerve does not innervate the glutes, and the obturator nerve innervates muscles in the medial thigh.

The short head of the biceps femoris is the only muscle of the posterior thigh that is not part of the "hamstring" muscle group. It is not cosnidered a hamstring muscle because it only crosses the knee joint; it does not act on the hip joint.

Only the short head of the biceps femoris is innervatd by the common fibular division of the sciatic nerve. The long head of the biceps femoris, the semimembranous, and the semitendinous are innervated by the tibial division of the sciatic nerve. The gluteus maximus is innervated by the inferior gluteal nerve.

All of the incorrect answer options are muscles of the anterior compartment of the leg. Muscles of the anterior compartment are involved in dorsiflexion of the ankle and are all innervated by the deep fibular nerve.

The fibularis longus is a muscle of the lateral comaprtment of the leg. Muscles of the lateral compartment of the leg are innervated by the superficial fibular nerve.

The flexor digitorum brevis is sandwiched between the plantar aponeurosis and the tendons of the flexor digitorum longus. It flexes the lateral four digits at the proximal interphalangeal joints.