Muscles of the Upper Arm Quiz

See Brachialis. Option A is correct because brachialis is the primary flexor of the elbow and its action does not depend on whether the forearm is turned palm up or palm down. The reason is its attachment: brachialis arises from the front of the lower humerus and inserts on the ulnar tuberosity, a roughened area just below the elbow joint on the ulna. The ulna does not rotate during pronation and supination (the radius rotates around it), so a muscle attached to the ulna pulls the same way whatever the position of the forearm. Brachialis lies deep to biceps brachii and forms the floor of the cubital fossa, the triangular hollow at the front of the elbow. Biceps and brachioradialis also flex the elbow, but brachialis is the strongest of the three. Like biceps, it is supplied by the musculocutaneous nerve. Memory aid: brachialis is the workhorse tied to the ulna, the bone that does not rotate, so it always does its job.

• Muscle: brachialis is the primary flexor of the elbow.
• Insertion: it inserts on the ulnar tuberosity of the ulna, which does not rotate in pronation and supination.
• Forearm position: its action is the same whether the palm faces up or down.