Skeletal: striated, primarily voluntary. Cardiac: striated involuntary myocardium. Smooth: nonstriated involuntary tissue in hollow organs/vessels.
Whole muscle → fascicles → muscle fibers → myofibrils → sarcomeres → myofilaments. Epimysium surrounds whole muscle, perimysium fascicles, endomysium individual fibers.
Actin thin filaments and myosin thick filaments interact during contraction. Calcium exposes binding sites; ATP is required for cross-bridge cycling and detachment.
A motor neuron releases acetylcholine at the NMJ, initiating muscle-fiber excitation. A motor unit is one motor neuron plus the fibers it innervates. Recruitment increases force by activating additional motor units.
Concentric: force while shortening. Eccentric: force while lengthening. Isometric: force without meaningful change in muscle length/joint angle.
Type I fibers are relatively fatigue resistant and oxidative; Type II fibers generally produce faster/more powerful contractions with subtype differences. Real muscles contain mixtures.
Parallel/fusiform fibers favor excursion; pennate arrangements pack more fibers into an area and favor force. Bones and joints form lever systems. Human movement often trades mechanical advantage for speed/range.
Muscle tone is ongoing low-level neural activation, not simply “tight fascia.” Posture is variable and task-dependent; avoid diagnosing pain solely from visual posture.
Be able to identify the major structures, state their functions, connect the system to relevant pathology and explain how the information changes massage safety or treatment planning.