A section of a myofibril from one z-disc to another z-disc. The contractile unit.

The thin protein filament anchored to a z-disc

The thick protein filament with protruding "heads"

An actin-binding protein which regulates muscle contraction. The "bars" keep actin and myosin from binding

A protein which acts as a "lock," keeping actin blocked until it binds to calcium

The "key" that unlocks troponin to allow actin and myosin to bind.

Contraction where myofilaments slide and the muscle shortens

Contraction where myofilaments do not slide due to muscles being pitted against something immovable.

Attachment to the immovable or less movable bone

Attachment to the movable bone

Movement that decreases the angle of a joint

Movement that increases the angle of a joint

Movement beyond the normal limit of motion

Moving limb away from the mid-line of the body

Moving limb toward the mid-line of the body

Lifting of superior surface of the foot toward shin

Depressing foot away from the shin

Movement of radius/ulna so palms face anteriorly

Movement of radius/ulna to cross so palms face posteriorly