cardiac - Graphics are used with permission of: Pearson...

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Cardiac Action Potential Graphics are used with permission of: Pearson Education Inc., publishing as Benjamin Cummings (http://www.aw- bc.com) Page 1. Introduction • The coordinated contractions of the heart result from  electrical changes that take place in cardiac cells. Page 2. Goals •   To   understand   the   ionic   basis   of   the   pacemaker  potential   and   the   action   potential   in   a   cardiac  autorhythmic muscle cell. • To understand the ionic basis of an action potential in a  cardiac contractile (ventricular) cell. • To understand that autorhythmic and contractile cells  are electrically coupled by current that flows through  gap junctions. Page 3. Intrinsic Conduction System • Cardiac autorhythmic cells in the intrinsic conduction  system   generate   action   potentials   that   spread   in  waves to all the cardiac contractile cells.  This action  causes a coordinated heart contraction.   Of all the  cells in the body, only heart cells are able to contract  on   their   own   without   stimulation   from   the   nervous  system.
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Page 4. Gap Junctions • Action potentials generated by autorhythmic cells create  waves of depolarization that spread to contractile cells  via gap junctions. • Label the parts of this diagram: Page 5.  Depolarization vs. Repolarization • If depolarization reaches threshold, the contractile cells,  in turn, generate action potentials, first depolarizing  then   repolarizing.   After   depolarization,   the   cardiac  myofibrils in contractile cells slide over each other  resulting in muscle contraction.   After repolarization  these cells relax. **   You may repeat the animation again if you wish by clicking on the  autorhythmic cell again. **   Now is a good time to go to quiz question 1: • Click the Quiz button on the left side of the screen. • After answering question 1, click the Back to Topic button on the left  side of the screen. • To get back to where you left off, click on the scrolling page list at the  top of the screen and choose "6. Autorhythmic Cell Anatomy".  Page 6. Autorhythmic Cell Anatomy • Embedded in the plasma membrane of an autorhythmic  cell we see several protein channels that allow ions to  move into or out of the cell.   These are crucial for  generating an action potential:
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1. Sodium Channels - allow sodium ions to enter the  cell 2. Fast Calcium Channels - allow calcium ions to enter  the cell. 3.   Potassium   Channels   -   allow   potassium   ions   to 
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cardiac - Graphics are used with permission of: Pearson...

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