What is the primary bone of the upper arm?

The primary bone of the upper arm is the humerus. This long bone extends from the shoulder to the elbow and plays a crucial role in the function and movement of the arm. It serves as an attachment site for many muscles responsible for shoulder and elbow movements. The proximal end of the humerus fits into the glenoid cavity of the scapula, forming the shoulder joint, while the distal end connects with the radius and ulna at the elbow joint. This structure allows for a wide range of motion, including flexion, extension, and rotation in the arm.

In contrast, the radius and ulna are located in the forearm and primarily function in the movement and stabilization of the wrist and hand. The carpal bones make up the wrist and do not contribute to the structure of the upper arm. Understanding the anatomy of these bones is essential for comprehending how the upper limb operates as a whole.