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Control of Heart Rate

The heart is a muscular organ composed of cardiac muscle that contracts and relaxes automatically, independent of the nervous system. It consists of two atria and two ventricles, with coordinated contractions essential for effective blood circulation. The cardiac cycle alternates between systole (contraction) and diastole (relaxation). The sinoatrial (SA) node functions as the heart's pacemaker, initiating atrial contractions, while the atrioventricular (AV) node facilitates ventricular contractions. Factors like exercise and adrenaline influence heart rate, ensuring timely blood flow.

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Control of Heart Rate

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Presentation Transcript

  1. Control of Heart Rate IB Topic 6.2

  2. Your Heart is a Muscle • Cardiac muscle • Spontaneously contracts and relaxes without nervous system control • Two atria • Relatively thin walls; receives blood • Two ventricles • Relatively thick walls; pumps blood • Needs to be controlled in order to keep the timing of the contractions unified

  3. Cardiac Cycle • The heart contracts and relaxes in a rhythmic cycle • When the heart contracts, it pumps blood • When the heart relaxes, its chambers fill with blood • One complete sequence of pumping and filling is called the cardiac cycle

  4. Systole and Diastole • Systole: • Contraction phase • Diastole: • Relaxation phase • AV valves • Between atrium and ventricle • Semi-lunar valves • Between two exits (L ventricle and aorta & R ventricle and pulmonary artery)

  5. Maintaining Your Beat • The right atrium has a mass of tissue within its walls near the superior vena cava • Called the sinoatrial node (SA node) • It acts as the pacemaker for the heart • It sends out an electrical signal to initiate the contraction of both atria • For a person with a resting heart rate of 72 beats a minute, signals from SA node are sent out every 0.8 seconds

  6. AV node • Also within the right atrium is another mass of tissue near the base • Called the atrioventricular node (AV node) • Receives signal from SA node, waits ~ 0.1 seconds, and sends out another electrical signal • This signal goes to the muscular ventricles, causing them to contract

  7. Therefore … • Both atria contract first, then both ventricles contract together

  8. Physiological Cues • The SA node sets the tempo for the entire heart • Tempo may be influenced by: • Exercise (increased demand for oxygen and your cells are producing more carbon dioxide) • High levels of CO2 trigger the medulla  signal to cranial nerves  increase heart rate • Chemicals • Adrenaline • High stress  adrenal glands secrete adrenaline into your blood stream • Adrenaline causes the SA node to “fire” more frequently

  9. Animation • http://www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_electrical.html

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