Lab 6: Heart Conduction System PDF

## LAB 6! ### Heart Conduction System: Simultaneous contraction of the atria followed by the ventricles for proper cardiac function. ### Autorhythmicity: A unique property of cardiac muscle is that cardiac muscle fibers are capable of self-depolarizing without an external stimulus. They can spon...

## LAB 6! ### Heart Conduction System: Simultaneous contraction of the atria followed by the ventricles for proper cardiac function. ### Autorhythmicity: A unique property of cardiac muscle is that cardiac muscle fibers are capable of self-depolarizing without an external stimulus. They can spontaneously depolarize at regular intervals, which in turn causes heart muscle to contract. ### Sino-atrial Node (SA Node): Where depolarization of heart begins and radiates in all directions. Wave of depolarization moves towards the left side. ### Gap Junctions: Depolarization of heart moves from cell to cell. Housed within intercalated discs. ### Fibrous Ring: Between atria and ventricles insulates the ventricles from electrical activity occurring in the atria. ### Atrioventricular (AV) Node: Only point in heart where electrical activity from atria can affect ventricles. Once depolarized, the impulse is conducted down the atrioventricular bundle and the right/left AV bundle branches towards the apex of the heart. Then through purkinje fibers. ### Purkinje Fibers (Cardiac Conduction Fibers): Rapid conducting, large diameter fibers that penetrate the cells of ventricular myocardium. ### Electrocardiograms (ECG): Follow the electrical activity (depolarization & repolarization waves) as they spread across the heart. Can be detected at the surface of the skin because of salty composition of body fluids (excellent conductor). * One electrode on right wrist, one on left wrist, third on left leg. * **Lead Ⅰ** Two electrodes working together to measure the potential difference between two points. * **Lead Ⅰ** Positioning of positive (red) recording electrode on the left leg & negative (white) on right wrist. ##### Figure 6.1 A typical ECG recording. **T-wave**: Repolarization of cardiac muscle (ventricular). **QT Interval**: Time between QRS complex to end of T-wave. #### P-wave: Spread of depolarization (AP) from SA node to cardiac muscle of atria. #### P-Q Wave: Delay accompanying excitation of AV node. AV node has very small diameter, so take longer for AP to reach AV bundle. This allows atria to finish pumping blood to ventricles so that atria can relax and ventricles contract. #### QRS Complex: Also atrial repolarization (ventricular depolarization). * **Q**: depolarized AV bundle at superior portion of IV septum. Impulse moves left to right across septum. * **R-spike**: Depolarization of Purkinje fibers in both ventricles. * **S**: Depolarization of fibers (tips of ventricles) completes.