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BIO 203 Lecture 12 - March 6th 2007 BIO 203 Lecture 11...

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March 6 th , 2007 BIO 203 Lecture 11 Muscles, Skeletons and Locomotion Skeletal Muscle o Multinuclear, every fiber is one cell, very long o Highly organized actin and myosin gives rise to “striations” o Function is voluntary movement Cardiac Muscle o Extensively branched, striated, with a single nucleus o Connected by intercalated disks o Joined together by gap junction (space within one cell which allows things to go from one cell to another), one action potential leaks sodium through to all cells through the gap junctions, causes a depolarization in those cells surrounding it, which causes them to fire action potentials, extreme degree of coordination of contraction, entire ventricle contracts as a whole. o Forms an electrical syncytium o Doesn’t need a neuron to fire an action potential o Pacemaker potential, depolarize without signal, auto rhythmic Smooth muscle o Spindle shaped, have single nucleus o Poorly organized actin and myosin o Most blood vessels have smooth muscle, part of wall of digestive system, involuntary movement o Varied properties, some stimulated by neuron, cannot contract unless stimulated, some are auto rhythmic Mot end Plate axons of motor neurons innervate skeletal muscle cells Sliding Filament Hypothesis o Striated muscle has a characteristic alternate light and dark banding pattern, look up on slides In sarcomere, actin is 1 um long, myesin is 1.65 um long If you stretch a muscle to longest length, actin at z lines, myesin in middle, actin again Cant develop tension at 3.65 um, so stretched out so actin and myesin cant contact
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