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Control of Heart Rate

Control of Heart Rate . IB Topic 6.2 . 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

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Control of Heart Rate

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  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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