Natural Excitation of The Heart Guyton 2011 pages

Natural Excitation of The Heart Guyton 2011 pages 115 -120 Berne 2008 pages 302 -309

Natural Excitation of The Heart Excitatory and Conductive System of the Heart To cause rhythmical contraction of the heart muscle Conducting impulses rapidly through the heart. Is susceptible to damage by heart disease, especially by ischemia of the heart tissues

Natural Excitation of The Heart SA Node = normal pacemaker Have two cell type Pacemaker Cells (Small, round cells having few organelles and myofibril) Conductor Cells (Slender, elongated cells) RMP is much less negative Lack the i. Kl, then the ratio of g. K to g. Na during phase 4 is much less

Natural Excitation of The Heart SA Node = normal pacemaker Change the Heart Rate Change the slope of Phase 4 Change threshold Potential Change the RMP Normal rhythm = 70 – 80 beats/min

Natural Excitation of The Heart K Ca SA Node = normal pacemaker N Ca , a Depolarization and repolarization is slower in slow responses

Natural Excitation of The Heart Internodal Pathways

Natural Excitation of The Heart AV Node Regions AN region (transitional zone) N region (mid portion) NH region Cause of the Slow Conduction Mainly by diminished numbers of gap junctions One-way conduction Normal rhythm = 40 – 60 beats/min

Natural Excitation of The Heart Purkinje fibers Cause of the Rapid Conduction mainly by increased numbers of gap junctions Normal rhythm = 15– 40 beats/min

Natural Excitation of The Heart Summary of the Spread of the Cardiac Impulse Through the Heart (second)

Natural Excitation of The Heart Impulse Velocity in Different Part of the Heart Tissue Conduction Rate (m/s) SA node 0. 05 Internodal Pathways 1 AV node 0. 05 Bundle of His 1 Left and Right Bundles 2 Purkinje System 4 Ventricular Muscle 1

Natural Excitation of The Heart Points Ectopic Pacemaker Stokes - Adams Syndrome Overrdrive Suppression

Natural Excitation of The Heart Effect of ANS of cardiac rhythmicity

Natural Excitation of The Heart Effect of ANS of cardiac rhythmicity Sympathetic division Parasympathetic division Innervates all areas Mainly innervates nodes Norepinephrine Increased permeability to Na and Ca Acetylcholine Increased permeability to K Decreases Heart Rate Increases the overall activity of the heart

Natural Excitation of The Heart Reentry Phenomenon

Natural Excitation of The Heart Reentry Mechanisms Pathway around the circle is too long Like cardiac dilation Velocity of conduction becomes decreased Blockage of the Purkinje system, Ischemia of the muscle, High blood potassium levels The refractory period of the muscle shortened in response to various drugs, such as epinephrine or after repetitive electrical stimulation

Natural Excitation of The Heart Global Reentry

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