Final answer:
The biceps brachii is responsible for elbow flexion, while the triceps brachii is responsible for elbow extension. The brachialis and brachioradialis assist in forearm flexion.
Step-by-step explanation:
The biceps brachii is a prime mover for elbow flexion. This means that when the biceps contract, they pull on the forearm to produce a bending motion at the elbow. The biceps brachii also plays roles in supinating the forearm at the radioulnar joints and flexing the arm at the shoulder joint. On the other hand, the triceps brachii are responsible for elbow extension, which is the straightening of the elbow. The brachialis and brachioradialis are synergist muscles that assist in the flexion of the forearm alongside the biceps brachii.