How does the biceps and triceps work?

Biceps brachii:

The biceps brachii is a two-headed muscle located at the front of the upper arm. It is responsible for flexing the elbow and supinating the forearm (turning the palm upwards).

The biceps brachii has two heads: the long head and the short head. The long head originates from the scapula (shoulder blade) and the short head originates from the humerus (upper arm bone). Both heads attach to the radius (one of the two bones in the forearm).

When the biceps brachii contracts, it flexes the elbow by pulling the forearm towards the upper arm. It also supinates the forearm by rotating it so that the palm faces upwards.

Triceps brachii:

The triceps brachii is a three-headed muscle located at the back of the upper arm. It is responsible for extending the elbow and stabilizing the shoulder joint.

The triceps brachii has three heads: the long head, the medial head, and the lateral head. The long head originates from the scapula, the medial head originates from the humerus, and the lateral head originates from both the scapula and the humerus. All three heads attach to the ulna (the other bone in the forearm).

When the triceps brachii contracts, it extends the elbow by straightening the arm. It also helps to stabilize the shoulder joint by preventing it from dislocating.