Motor unit
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A motor unit is a single α-motor neuron and all of the corresponding muscle fibers it innervates. Groups of motor units often work together to coordinate the contractions of a single muscle; all of the motor units that subserve a single muscle are considered a motor unit pool. The number of muscle fibers within each unit can vary: thigh muscles can have a thousand fibers in each unit, eye muscles might have ten. In general, the number of muscle fibers innervated by a motor unit is a function of a muscle's need for refined motion. Muscles requiring more refined motion are innervated by motor units that synapse with fewer muscle fibers.
In medical electrodiagnostic testing for a patient with weakness, careful analysis of the "motor unit action potential" (MUAP) size, shape, and recruitment pattern can help in distinguishing a myopathy from a neuropathy.
[edit] See also
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skeletal muscle/general: epimysium, fascicle, perimysium, endomysium, muscle fiber, myofibril
sarcomere (a, i, and h bands; z and m lines), myofilaments (thin filament/actin, thick filament/myosin, elastic filament/titin), tropomyosin, troponin (T, C, I)
neuromuscular junction, intrafusal muscle fiber, extrafusal muscle fiber, motor unit, muscle spindle, sliding filament mechanism
myoblast, satellite cells, sarcoplasm, sarcolemma, sarcoplasmic reticulum, T-tubule
