Anim cardiac conduction worksheet PDF

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Cardiac Conduction Instructions: please answer the questions below. 1. What is the function of the Conduction System?

The conduction system determines the sequence by a pathway. In order for the heart to function properly all of its cells must contract in a specific sequence. Your Answer

2. Cardiac cells are connective and autorhythmic. What does this mean? Connective. is action potentials that can propagate from one cell to another via gap junctions. Autorhythmic are cells that can excite themselves spontaneously and contract at a regular rhythm.

3. Cells from different parts of the heart’s conduction system have different natural rhythms. What are the average beats per minute at each of the following parts of the heart? a. Sinoatrial Node (SA) around 100 beats/min b. Atrioventricular Node (AV) 40 to 50 beats/min c. Ventricles 20 to 40 beats/min

4. What is the function of the SA Node? Describe how this happens. The SA node triggers contraction because it depolarizes at a faster rate than other parts of the conduction system. The wave of excitation from the SA node travels through the atria and triggers the atria to contract and move additional blood into the ventricles.

5. The AV node starts a series of events that leads to ventricular contraction. Describe this series of events. The AV node is the only connection between the atria and ventricles. Once the signal passes it propagates through the ventricular portion of the conduction system. The conduction myofibers then directly stimulate the cardiac cells in the ventricles to contract. During ventricular contraction, blood is squeezed out from the apex to the base and into the pulmonary trunk and aorta.

6. Describe the contraction signal timing as it passes from the SA Node to the AV Node, through the AV Bundle, to the apex, on to the base of the heart. The signal travels its route from the SA node to the ventricles. The signal passes through the atria very quickly and then slows when it reaches the AV node. The slowing occurs because the AV node fibers have smaller diameters. The delay allows the atria to fully contract and increases blood volume in the ventricles before ventricle contraction begins. The signal then quickly passes through the AV bundle and excited the apex and base of the ventricles, which begins contraction.

7. What happens at each of the following points of a normal ECG? P-

atrial depolarization-100 beats/min

QRS -

ventricular depolarization-37 beats/min

T-

ventricular repolarization

8. Contrast a healthy heart ECG with an abnormal one in which ventricular excitation is independent of atrial excitation (P waves). In an abnormal ECG trace it can be seen that the ventricular excitation is independent of atrial excitation (P waves). The pace of ventricular contraction is being determined by the ventricles’ natural rhythm, not from excitation generated by SA node. The SA node’s signals are not successfully moving along their normal path to the ventricles.

9. Contrast the resting potential of typical myocardial cells with that of SA node cells.

A typical contractile cell in the myocardium has a resting membrane potential. The resting membrane potential of cells in the SA node is not fixed and is known as the pacemaker potential.

10. Identify each of the following parts of an action potential on graphs of SA Nodal cells and ventricular cells. Explain what is happening during each stage. SA Node Pacemaker Potential Each healthy heartbeat starts with a pacemaker potential in which autorhythmic cells spontaneously excite themselves and neighboring cells. SA Node Threshold The membrane potential spontaneously and gradually becomes more positive until threshold is reached. SA Node Depolarization This threshold triggers rapid depolarization. SA Node Repolarization repolarization follows and the return of the cell to the resting potential. Ventricular Resting Potential Membrane potential remains steady until some stimulus causes it to exceed threshold. Ventricular Threshold Threshold is exceeded and causes a triggering of depolarization. Ventricular Depolarization Rapid depolarization is triggered. Ventricular Plateau A plateau follows during which the cell remains depolarized. Ventricular Repolarization

Repolarization follows and the return of the cell to the resting potential.

11. What two factors combine to determine heart rate? SA node’s rate of firing and the ANS.

12. a. Contrast the affects of acetylcholine and norepinephrine on heart rate. Ach secreted from parasympathetic neurons, decreases heart rate. Norepinephrine (ne) secreted from sympathetic neurons, increases heart rate. b. Which is secreted by parasympathetic neurons and which is secreted by sympathetic neurons? Ach is secreted from parasympathetic neurons and norepinephrine is secreted from sympathetic neurons....