Final answer:
The biceps brachii, brachialis, and brachioradialis are muscles on the front of the upper arm responsible for flexing the elbow and are known as prime movers in this action. The correct answer is B) Prime movers.
Step-by-step explanation:
When considering the flexing of the elbow, the muscles involved are the biceps brachii, brachialis, and brachioradialis, which are all located on the front of the upper arm. These muscles are responsible for flexing the forearm, and are collectively known as prime movers or agonist muscles when talking about this specific action. They work in conjunction to produce the motion of bending the elbow and moving the forearm towards the shoulder.
The correct answer to the student's question is B) Prime movers. The biceps brachii is a two-headed muscle that crosses the shoulder and elbow joints and is involved not only in flexing the forearm but also in supinating the forearm and flexing the arm at the shoulder joint. The brachialis lies beneath the biceps brachii and provides additional power in flexing the forearm. Lastly, the brachioradialis, located in the forearm, can flex the forearm both rapidly or assist in lifting a load slowly. These muscles form the anterior compartment and are key elements in movements such as flexing the elbow.