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Physio Lecture 21
Cardiac Structure and Activation
| Term | Definition |
|---|---|
| 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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