The sartorius, semitendinous and gracilis all make up the pes anserine tendon. Vastus medialis, although on the medial aspect of the knee, does not make up this muscle group as it inserts to the tibial tubercle via the patellar tendon. 

The iliopsoas muscle is composed of the iliacus and psoas major muscles. It functions as a flexor of the thigh at the hip joint and laterally rotates it. It's also capable of flexing the trunk on the hip as in sitting up from the supine position.

The tibialis anterior and extensor digitorum longus muscles both dorsiflex the foot at the ankle joint; the tibialis anterior also inverts the foot at the intertarsal joints and the extensor digitorum longus extends the proximal and distal phalanges. The gastrocnemius and soleus muscles are plantarflexors of the foot at the ankle joint. The gastrocnemius also flexes the leg at the knee joint.

The quadriceps femoris group of muscles are the main extensors of the leg at the knee joint. They consist of the rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis muscles. The rectus femoris muscle also flexes the thigh at the hip joint.  

In order to cause flexion or extension of a joint, a muscle must originate on one side of the joint and insert on the other. In other words, the muscle body must cross the joint in order to affect it.

The biceps brachii, brachialis, corocobrachialis, and brachioradialis originate from the scapula or humerus and insert on the radius or ulna. Each of these muscles thus crosses the elbow. In contrast, the flexor carpi radialis originates on the radius and inserts on the second metacarpal. When contracted, the flexor carpi radialis causes flexion of the hand at the wrist, but does not affect the position of the forearm.

A synergist is, by definition, a muscle that aids an agonist in its movement. The biceps brachii acts to flex the forearm. The brachialis also flexes the forearm and helps stabilize the motion created by the biceps brachii.

The triceps brachii is an antagonist to the biceps brachii, working to extend the forearm rather than flex. The pectoralis major helps to adduct the arm at the shoulder and the rectus femoris extends the leg at the knee.

The ulnar nerve is responsible for all motor innervation of the hand except for the thenar muscles and the lateral two lumbricals, which are innervated by the recurrent branch of the median and the palmar digital nerves of the median nerve, respectively.

The two most common sites for ulnar nerve injury are where the ulnar nerve passes posterior to the medial epicondyle of the humerus and on the medial side of the wrist near the pisiform bone. If the site of injury is where the ulnar nerve passes lateral to the pisiform bone in the wrist, the patient will still be able to flex her medial two distal phalanges. Remember, in the forearm, the ulnar nerve innervates the medial two tendons of the extensor digitorum profundi and the median nerve innervates the lateral two extensor digitorum profundi.

The flexor carpi radialis passes through a small gap in the flexor retinaculum, not through the carpal tunnel.

The carpal tunnel houses the median nerve and tendons for three muscles: the flexor digitorum profundus, the flexor digitorum superficialis, and the flexor pollicis longus. Compression of the carpal tunnel such that it affects the median nerve results in carpal tunnel syndrome.

The deltoid muscle is a triangle-shaped muscle responsible for the abduction of the arm beyond the initial 15 degrees accomplished by the supraspinatus muscle (rotator cuff muscle). The deltoid is innervated by the axillary nerve.

The infraspinatus is another muscle of the rotator cuff, and serves to externally rotate the arm at the shoulder. The trapezius serves some abduction functions, but cannot generate the same range of motion as the deltoid. The trapezius is more closely linked to establishing posture and maintaining shoulder position than active abduction.

The rhomboid major and rhomboid minor muscles are responsible for retraction and elevation of the scapula. Both the rhomboid major and minor are innervated by the dorsal scapular nerve. The levator scapulae also helps elevate the scapula. The important distinction is that the rhomboids both originate from the vertebrae and insert on the medial border of the scapula. It is this pathway that allows for both elevation and retraction.

The trapezius helps elevate the scapula and raise the upper limb above the head, but is not associated with retraction of the scapula. The deltoid muscle is responsible for abduction of the arm beyond the initial fifteen degrees accomplished by the supraspinatus muscle. The latissimus dorsi extends, adducts, and medially rotates the arm.