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Unformatted text preview: uscle 1/4 original size) – the muscle is eventually replaced by fibrous tissue (irreversible) Muscle Hypertrophy Increase in the size of muscle fibers secondary to increase in myofibrils, mitochondria, SR, nutrients, and energy supplying molecules. • muscle size controlled by growth hormone, testosterone, and exercise. Cardiac Muscle • involuntary • striated • have only a single centrally located nuclei • exhibit branching Consist of two separate networks:atria and ventricles • fibers in each network are connected to each other via intercalated disks (irregular transverse thickening of the sarcolemma). • the discs contain gap junctions, which conduct muscle action potentials from one fiber to the other. This enables each network to conduct as a unit. Cardiac Muscle Fiber characteristics • contracts continuously without stopping – requires a constant supply of energy and oxygen • fibers can contract without nervous stimulation (autorhythmicity) – is stimulated by a pacemaker and a specialized conduction tissue. – nervous stimulation only modulates contractions. – pacemaker fires at a greater rate than fibers,thus, establishing the contraction rate. • has a long refractory period – prevents complete tetanus Smooth Muscle • • • • Involuntary single centrally located nuclei nonstriated also has intermediate filaments as well as thick and thin myofilaments – i...
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- Spring '06