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BIOL1412 02 26 2014.docx

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Biological Sciences
Course Code
BIOL 1412
Paul Messing

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BIOL1412 o2 26 2014 Cardio Physiology  Parts: 1) Heart – dual pump with valves (Fig. 18.4)  Muscle cells connected by gap junctions 2) Conduction System  Non­contractile cardiac muscle cells – modified to initiate & distribute impulses throughout the heart  Produce APs spontaneously (no stimulus) BUT at different rates (Fig. 18.5)            Parts: a) Sinoatrial (SA) node – in right atrium  Rate = 100 APs/min (modified by PSNS to be 75 APs/min.) (at rest)  Produces APs faster than other areas therefore = pacemaker b) Atrioventricular (AV) node – in right atrium  Rate = 50 APs/min c) Bundle of His (AV Bundle)  Originates at AV node  ONLY route for electrical activity to go from atria to ventricles + Bundle  Branches (right and left)  30 APs/min d) Purkinje Fibers  Terminal fibers – stimulate contraction of the ventricular myocardium  30 APs/min  Pathways of APs in the Heart:  ventricular contractile myocardium (or cardiac muscle cells)  if conduction system is damaged, next fastest part becomes pacemaker  ie. if SA node is damaged, AV node takes over (atria may not contract + ventricles contract at AV  speed = 50 beats/min.)  Artificial pacemakers – stimulate if SA or AV node is damaged  APs in SA & AV nodes:  Cells = non­contractile autorhythmic cardiac muscle (self­excitable)  Threshold = ­40 mV (Fig. 18.14)   Phases of Pacemaker Activity:  1) Pacemaker Potential + + 
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