Final answer:
The triceps brachii is located at the back of the upper arm and is responsible for extending the forearm at the elbow joint.
Step-by-step explanation:
The triceps brachii is a large, three-headed muscle located at the back of the upper arm. Its primary function is to extend the forearm at the elbow joint. This muscle works antagonistically with the biceps brachii, which is responsible for flexing the forearm. When you want to straighten your arm, your triceps contracts while the biceps relaxes. In daily activities, the triceps is less used compared to the biceps, as most routine tasks, like lifting, require the elbow to be flexed against gravity.
It is important to note that aside from its primary function, the triceps also plays a role in the stability of the shoulder joint as one of its heads (the long head) attaches to the scapula. This configuration is essential as muscles typically come in pairs to enable both the opening (extension) and closing (flexion) of limbs. Consequently, the triceps allows us to push things away from the body and perform tasks involving straightening the arm. Understanding the triceps' role and mechanics can also extend to applications in sports and physical rehabilitation.