CONTROL OF HEART RATE

• The autonomic nervous system controls the involuntary action of smooth and cardiac muscles, and glands.
• The autonomic nervous system is divided into the sympathetic and parasympathetic nervous system.
• The sympathetic and parasympathetic nervous systems are antagonistic with each other: they act in opposite ways.
• The heart is composed of a type of muscle called cardiac muscle. Cardiac muscle is myogenic.
• • Myogenic refers to the muscle contraction being initiated from the muscle itself, rather than from a nerve.
• Label the heart:

  A) Aorta

  B) Left ventricle

  C) Right atrium

  D) Vena cava

  E) Pulmonary vein

  F) Pulmonary artery

  
• Non-conducting tissue between atria and ventricles prevents immediate contraction of ventricles by stopping the wave of electrical activity passing down the outer wall of the ventricles.
• special cardiac muscle tissue carries wave of electrical activity across the atria
• Cardiac cycle

  1. SAN sends wave of electrical activity across atria causing atrial contraction;
  2. Non-conducting tissue prevents prevents wave of electrical activity reaching the ventricles/prevents immediate contraction of ventricles;
  3. AVN delays wave of electrical activity whilst blood leaves atria and the ventricles fill;
  4. AVN sends wave of electrical activity down Bundle of His/Purkyne fibres;
  5. This causes ventricles to contract from base up.
• • Exercise means you have to increase your heart rate to deliver oxygen (and glucose) faster to the respiring muscles;
  • Faster heart rate is linked to higher blood pressure. Blood pressure cannot get too high (damaging to blood vessels) or too low (blood moves too slowly - not enough oxygen delivered to tissues).

  so, Heart rate can be controlled involuntarily using the autonomic nervous systems.
• medulla (contains “cardiac centre” for heart rate control)
• More exercise → more aerobic respiration → increased carbon dioxide concentration in blood.

  Carbon dioxide dissolves in water to produce an acidic solution.

  The pH of the blood therefore falls.
• Higher heart rates lead to higher blood pressure (since more blood is being pumped per unit time);

  Lower heart rates lead to lower blood pressure;

  Changing the heart rate can therefore be used to maintain blood pressure at an optimal level.
• • Cardiac output is the volume of blood pumped by the heart per minute.
• • Stroke volume is the volume of blood pumped by the heart per beat.
• • Heart rate is the number of beats per minute.
• Cardiac output = Stroke Volume x Heart Rate