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Physio Lecture 21

Cardiac Structure and Activation

Cardiac Cell Structure Cylindrical shaped cells. Interrelated disks join cells end to end. Filaments - as in skeletal msucle. Thin filaments activaiton by Ca2+ binding to troponin.
Intercalated Disks Strong connections between cells. Desmosomes for strength. Gap junctions for electrical activation spread.
Circulatory Flow Circut Sys: LV to aorta to body to vena cava to RA. Pul: RV to pulmonary artery to lungs to pulmonary vein to LA. Valves maintain direction of flow.
Cardiac Activation Structures Activation pathway has autorhythmic cells.
Atria Site of normal heart beat initiation.
SA Node In right atrium. Depolarizes to threshold starts AP. Fastest depolarizer - no stable baseline membrane potential. The intermodal pathway connects the SA node to the AV node. Premature beats occur if the heartbeat starts elsewhere - not usually harmful.
Atrial Muscle Right atrium activated by SA node - spreads toward the LA using the interatrial pathway. Spread through gap junctions. Not autorhythmic - contraction spreads downward.
AV Node Electrical connection from atria to ventricles. Delays AP spread, allows ventricular filling to be completed. AV block produces separate atrial and ventricular activation.
Ventricles AP enters septum first, spreads to apex then up to ventricular muscle. V muscle contraction spreads upward.
Bundle of His Off of AV node down the septum.
Purkinje Fibers Branch off of septum to ventricular muscle. Activated by bundle of His though gap junction.
Ventricular Muscle Apex cells activated first by purkinje fibers, then muscle cell to cell through gap junction. Contraction spreads upward, forcing blood into aorta and pulmonary artery. No pacemaker activity.
Pacemaker Cells Autorythmic, no stable baseline potential. SA and AV nodes, some cells of B and H and purkinje fibers.
Depolarization Na+ entry to threashold. Opening of Ca2+ channels during AP. Opening of K+ channels during repolarization. Little Na+ influence on AP.
Neural Influences Sympathetic neurons-inc. depolarization. NE opens Ca2+ channels in atria and ventricles. Inc. heart rate and strength of contraction. Parasympathetic neurons (vagus n.)-Ach dec depolarization rate, Ach dec. Ca2+ channel opening in atria dec. heart rate
Electrocardiogram Sum of changes in cardiac AP's relation to cardiac AP. Detect changes in the sum of AP's. Changes in membrane potential detected by diff distances to leads.
Relation to Cardiac AP Ventricular Fibrilation - life threatening - no coordinated emptying - no blood delivery. Need electrical shock to recoordinate AP's.
P Wave Atrial depolarization. Start of atrial contraction.
QRS Complex Ventricular depolarization masks atrial repolarization. End of atrial contraction, start of atrial filling start of ventricular contraction.
T Wave Ventricular, repolarization. End of ventricular contraction, start of ventricular filling.
Created by: danamarie9323



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