Muscles, Movement and Support

Movement is one of the defining features of animals, allowing them to find food, escape predators, and reproduce. Locomotion depends on three components working together: a skeleton for support and leverage, muscles that generate force by contracting, and joints that allow controlled movement. Understanding how these parts interact, and how muscle contraction works at the molecular level, ties together structure and function at every scale.

Muscle Structure

Skeletal muscle is made of long fibers, each containing many parallel myofibrils. Myofibrils are divided into repeating units called sarcomeres, the basic contractile units. Each sarcomere contains two kinds of protein filament:

• Thick filaments made of myosin, which have projecting heads.
• Thin filaments made of actin, along with the re