The second sound (dupp) occurs as ventricles relax and aortic and pulmonary valves are closing. Cardiac Conduction system: Specialized cardiac muscle tissue conducts impulses throughout the myocardium and comprises the cardiac conduction system. A self-exciting mass of specialized cardiac muscle called the sinoatrial node (or pacemaker) is located on the posterior right atrium and generates the impulses for heart contraction. This node initiates impulses that spread throughout the myocardium and is self-exciting (-it does not require a signal from the nervous system). Impulses from the S-A node quickly spread throughout the atria and cause them to contract. Impulses also spread to the atrioventricular (A-V) node. The A-V node rapidly sends a signal down the AV bundle and into the interventricular septum. These impulses rapidly spread through Purkinje fibers into the walls of the ventricles and cause the ventricles to contract. ECG/EKG: The first wave, the P wave, corresponds to the depolarization of the atria. The QRS complex corresponds to the depolarization of ventricles and hides the repolarization of atria. The T waves end the ECG pattern and correspond to ventricular repolarization. Heart rate control: Cardiac Conduction System regulates heart rate at about 75 beats/minute. However, the amount of blood pumped at any one time must adjust to the current needs of the body (more blood needed during strenuous exercise). Autonomic Nervous System regulates the cardiac conduction system to meet the needs of the body. Sympathetic division-increases heart rate Parasympathetic division-decreases heart rate Other Factors the regulate heart rate: temperature- How does increasing Temperature affect heart rate? Increases heart rate hormones- How does epinephrine affect heart rate? Increases heart rate and also the contraction’s strength 4
drugs-How does caffeine affect heart rate? Increases heart rate Certain ions- What is hyperkalemia? Decreases heart rate and also the contraction’s strength 5
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