Muscles, skeletal, smooth, cardiac Healthcare professionals and scientists have carefully prepared this ALtruis Biomedical Network-affiliated site, intended for informational purposes only . An action potential is an electrical change across a cell membrane due to changes in the conduction of ions across the membrane. Nervous tissue is also an excitable tissue.
Muscle cells contain a contractile mechanism that is activated by the action potential.
Contraction by a whole muscle Isometric versus Isotonic Isotonic contractions are those when the tension on a muscle remains constant but the muscle shortens as in lifting a static amount of weight. Isometric muscle contractions occur when the muscle doesn't shorten as, for example when pushing against an immovable object like a wall. Isometric contraction differs from isotonic in that the myofibrils don't slide over each other much as force is developed. Sliding does occur in isotonic contractions and external work is performed. Motor unit concept The motor nerve and all the fibers it innervates is called the motor unit.