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21 Cards in this Set
- Front
- Back
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How cardiac differs from skeletal muscle
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Branched, connected @ intercalated disks w/ GJ - allow to function as synctium. No NMJ, t-tubules penetrate deeper; SR stores Ca and calsequestrin.
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calcium-induced calcium release
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Extracellular Ca entry triggers Ca release from SR, which triggers muscle contraction. **EC Ca critical for cardiac contraction, unlike skeletal.
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Ca and diastole
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pumps in SR and Sarcolemma pump Ca out of cytosol; Na/Ca exchanger also pumps Ca out of cell.
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Main determinant of force of cardiac muscle contraction
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Free intracellular calcium; it determines # of crossbridges pulling at a time. Can be increased or decreased for each AP
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main determinant of force of skeletal muscle contraction
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# of AP's firing on an alpha motor neuron or # of fibers recruited
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2 most effective ways of increasing intracellular concentration and force of contraction
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increase SR concentration of Ca (increase driving force) and increase # of open Ca channels or amt of time they are open (increase conductance)
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Mechanism for sympathetic increase in contractility in cardiac
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exercise/stress >> NE binds beta-1 AR >> increase CAMP & PKA >> phosphorylate Ca channels to up conductance and phosphorylate phospholamban on SR >> increase Ca entry and pumping >> increase Ca in SR >> Greater Ca influx during depolarization, greater Ca stored in SR and released during depol., Ca resequestered quickly
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what is Beta 1 AR
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GPCR G alpha S; increases camp and PKA
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What do catecholamines do
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increase peak force of contraction and rate of contraction and relaxation
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3 variables that determine # of crossbridges pulling (force of contraction) in cardiac
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contractility, preload, afterload
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smooth muscle cells
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small, spindle-shaped, adherins junctions and GJ. No sarcomeres, SR less developed.
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Excitation-contraction in smooth muscle
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Ca++ binds calmodulin >> MLCK activated >> phosphorylated myosin forms crossbridge w/ actin >> ATP breaks crossbridge >> hydrolyze ATP to reset myosin head.
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2 things that need to be true for cycle to continue
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Ca levels high; myosin is phosphorylated
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crossbridge cycling rate depends on
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MLC phosphorylation
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relaxation depends on
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MLC phosphatase.
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ways to regulate intracellular Ca in smooth muscle
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opening of voltage-gated channels on sarcolemma; SR release of calcium (via calcium-induced or IP3)
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RMP in smooth muscle based on
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K+/Na+ levels (atpase) -60mV
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depolarization process
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stimuli cause graded depolarization, activating voltage-gated Ca channels, Ca influx leads to contraction.
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basal tone in smooth muscle
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tonic depolarizing stimulus induces continuous partial depolarization. mediated by voltage-gated Ca channels
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vasoconstriction mechanism in smooth muscle
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NE and other constrictors bind GPCR q >> increase DAG >> PKC >> Ca influx. Also increase IP3 >> Ca release from SR.
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vasodilation mechanism in smooth muscle
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E and other dilators bind GPCR s >> PKA or PKG >> increase K+ conductance >> hyperpolarization >> less Ca influx >> less Ca >> vasodilation
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