The human skeleton has multiple functions, including protecting internal organs and creating new red blood cells, according to Minnesota State University. Perhaps the most important function of the skeletal system is to allow you to move efficiently. Without this ability, you would be vulnerable to danger, could not stay as healthy and could not participate in activities. The human skeleton is designed to facilitate specific kinds of movement.
According to Partners in Assistive Technology Training Systems (PATTS), the human skeleton moves primarily via a system of levers and axes. In the skeletal system, your bones usually are the levers, and the joints are the axes, or pivot points, on which the levers move.
Joints By Movement Amount
According to the Shock Family Web Page and PATTS, there are three types of joints related to movement based on the amount of movement allowed. These include immovable (fibrous), slightly movable (cartilagenous) and freely movable (synovial) joints. Fibrous joints are found in parts of the skeleton like the skull. Cartilagenous joints are found any where only partial movement is needed, such as in the spine. The majority of joints in the skeleton are synovial. They provide the most movement and are found in areas where flexibility is most important.
Joints By Movement Type
The Shock Family Web Page explains that the joints in the skeleton fall into categories based on the type of the movement. Hinge joints (e.g., elbows, knees) move only back and forth, allowing you to extend and retract a body part. Saddle joints (e.g., your bottom thumb joint) permit forward, backward and sideways movement, but don't permit full rotation. Ball and socket joints (e.g., hip joints) allow you to rotate in nearly all directions. Ellipsoids (e.g., wrist joints) are like ball and socket joints but without as much range of motion. Pivots (e.g., the neck) let a body part pivot on top of a central point. Gliding joints (e.g., middle feet joints) slide past each other.
According to Estrella Mountain Community College, the skeletal system depends on the muscular system to have the levers and axes work. Muscles shorten when engaged, and as a consequence, they pull the levers toward them. When the muscles relax, they lengthen, so the levers move away from them. The skeletal system also depends on the nervous system for movement, because the nervous system sends the messages to the muscles to contract or relax.
According to Estrella Mountain Community College, problems in skeletal movement may occur from disease or injury. Probably the most common example is arthritis. This is a condition in which the protective tissue and fluids that keep the levers and axes of the skeleton moving smoothly disintegrate or get inflamed. When this happens, decreased range of movement and pain occur. Sprains and tendon tears also impact movement.