IB DP Biology: SL复习笔记6.2.5 The Heart Rate

Heart Rate: Alteration by Nervous System

  • Although the heart muscle maintains a base heart rate via myogenic stimulation, there are several circumstances that can cause an individual's heart rate to change, e.g.
    • Exercise
    • Stress
    • Relaxation
  • The brain is involved in the regulation of heart rate, though it does not require conscious thought
    • The branch of the nervous system that does not require conscious thought is known as the autonomic nervous system
  • The area of the brain that controls heart rate is the cardiovascular centre, located in a region of the brain called the medulla
  • The medulla is found at the base of the brain near the top of the spinal cord
  • Two nerves connect the medulla with the sinoatrial node (SAN):
    • One nerve connects to the acceleratory centre, which causes the heart to speed up
      • This happens in response to low blood pressure, low oxygen concentrations and low pH
      • These changes might occur during exercise
      • The blood vessels dilate, causing a decrease in blood pressure
      • The muscle cells are using up oxygen at a faster rate, causing blood oxygen levels to drop
      • The production of carbon dioxide by respiring cells causes blood pH to decrease
    • The other nerve connects to the inhibitory centre, which causes the heart to slow down
      • This happens in response to high blood pressure, high oxygen concentrations and high pH
      • These changes are likely to occur when the body is at rest


The heart rate is controlled by the cardiovascular centre in the medulla

Heart Rate: Alteration by Hormonal System

  • Epinephrine, also called adrenaline, is produced by the adrenal glands, located above the kidneys, in times of fear, stress, or excitement
  • The brain controls the release of epinephrine from the adrenal glands
  • Epinephrine increases the heart rate and boosts the delivery of oxygen and glucose to the brain and muscles, preparing the body for ‘flight or fight’
    • Increased glucose and oxygen are needed by the cells for aerobic respiration to release energy, e.g. to fuel the muscles to move/run away!