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THE CONDUCTION SYSTEM (ELECTRICAL SYSTEM): REGULATION OF HEART RATE & THE AUTONOMIC NERVOUS SYSTEM Regulation of Heart Rate The normal heart rate in a resting adult is 60 to 100 beats per minute. Remember, "normal" means that most people have heart rates in this range most of the time. Small fluctuations outside the "normal" range do not necessarily indicate a problem. Some doctors might say the normal resting heart rate is 50 to 90 beats per minute. As you run, climb stairs, or exercise, the sinus node responds and your heart rate speeds up. Your heart beats faster with increased activity to send more blood to nourish your muscles. Along with exercise, several other things can increase the heart rate, including mental stress, tobacco, caffeine, alcohol, and certain prescription and nonprescription drugs. Alternatively, your heart rate normally slows during sleep and with some medications. Pulse rates in the range of 30 to 50 beats per minute are not unusual in healthy adults during sleep. The Autonomic Nervous System The message that prompts the sinus node to increase or decrease its rate is delivered by the autonomic nervous system. The autonomic nervous system automatically controls many functions in your body such as blood pressure, breathing, excretion, and heart rate. You do not have to decide consciously to breathe or to change your heart rate because the autonomic nervous system takes care of these decisions for you. It can make snap judgments. For instance, it can cause the sinus node to increase the heart rate to twice its normal rate within only 3 to 5 seconds. *38\252\8* Cardio & Blood |
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