How does the musculoskeletal system work to produce movement?

The skeletal system supports the body, protects organs and provides a framework against which muscles act. Bone also stores minerals and contains marrow involved in blood-cell production. The axial skeleton includes the skull, vertebral column, ribs and sternum; the appendicular skeleton includes the limb bones and their shoulder and pelvic girdles. During movement, a bone acts as a relatively rigid structure, a joint permits or constrains motion, and muscle tension transferred through tendons produces a turning effect.

A ligament connects bone to bone and contributes joint stability; it is not another name for a muscle tendon.

Locate the clavicle and scapula at the shoulder; humerus in the upper arm; radius on the thumb side and ulna on the little-finger side of the forearm in anatomical position; carpals, metacarpals and phalanges in the wrist, hand and fingers. The pelvis connects the trunk and lower limbs; femur, patella, tibia and fibula are associated with the thigh and knee/lower leg, while tarsals, metatarsals and phalanges form the ankle/foot/toes.

The tibia is the larger weight-bearing lower-leg bone; the fibula also contributes attachment and ankle stability. Correct identification makes a movement explanation more precise than simply saying that the leg bends.

Joint structure and movement are related. Fibrous joints join bones through fibrous tissue, as in skull sutures. Cartilaginous joints use cartilage, including the connection between vertebral bodies. Synovial joints have a joint cavity, articular cartilage and a capsule containing synovial fluid. They permit substantial movement, but their shape, supporting tissues and surrounding muscles constrain direction and range. Hinge joints such as the elbow mainly allow flexion and extension; the knee is a modified hinge.

Ball-and-socket joints at hip and shoulder allow movement in several planes. Pivot joints permit rotation, plane joints permit gliding, the thumb has a saddle joint, and the wrist includes a condyloid joint. These examples do not mean every joint has identical freedom.

Flexion generally decreases the angle at a joint and extension increases it. Abduction moves a limb away from the body’s midline; adduction returns it toward that line. Rotation turns around a longitudinal axis, and circumduction combines movements so the distal end traces a circle. At the ankle, dorsiflexion brings the top of the foot toward the shin and plantar flexion points the foot away. Pronation and supination describe forearm rotation; they are not synonyms for elbow bending.

Identify the joint, moving segment and phase before naming the action. Anatomical position provides the reference even when the performer is lying down or upside down.