Final answer:
The biceps brachii is a two-headed muscle responsible for flexing the forearm, supinating the forearm, and flexing the arm at the shoulder. Its contraction is facilitated by the tendons connecting the muscle to the upper arm and forearm.
Step-by-step explanation:
Description of the Biceps Brachii and Its Primary Function
The biceps brachii is a two-headed muscle that plays a critical role in the movement of the upper arm. This muscle spans across the shoulder and elbow joints, primarily functioning to flex the forearm. In addition to this, the biceps brachii assists in the supination of the forearm at the radioulnar joints, which is the rotation of the forearm that turns the palm upward, and it also contributes to flexing the arm at the shoulder joint.
Located deeper than the biceps brachii is the brachialis muscle, which provides additional power when flexing the forearm. Another muscle involved in this process is the brachioradialis, which can flex the forearm more quickly or help lift a load more slowly. These muscles, along with their associated blood vessels and nerves, make up the anterior compartment of the arm, also known as the anterior flexor compartment of the arm.
During a biceps brachii muscle contraction, the movement is facilitated by the belly of the muscle, which is the large mass at the center. Tendons from both ends of this belly connect to the bones; specifically, the tendons of the biceps connect the muscle to the upper arm and the forearm, enabling movement at these joints.