What type of joint connects the arm to the shoulder?

The arm connects to the shoulder through a ball and socket joint, which allows for a significant range of motion in multiple directions. This type of joint consists of a spherical head of one bone fitting into a cup-like socket of another bone. In the case of the shoulder, the humerus (the bone of the upper arm) fits into the glenoid cavity of the scapula (shoulder blade). This design enables the arm to move freely in various planes, such as lifting, rotating, and swinging, making it highly versatile for activities that require arm movement.

In contrast, the other types of joints provide more limited movement. Pivot joints allow for rotational movement around a single axis, which is not how the shoulder operates. Hinge joints only allow movement in one direction, similar to a door swinging open and closed, while gliding joints permit slight movements between flat surfaces, which does not account for the shoulder's extensive mobility.