Control of heart rate

• The sympathetic nervous system stimulates effectors and speeds up any activity in response to stressful stimuli to prepare the body for fight or flight response
• The parasympathetic nervous system inhibits effectors and slows down any activity which helps us conserve energy
• Coordination of a heartbeat

  1. Electrical waves are generated and sent out from the sinoatrial node, which initiates the heartbeat and determines the heart rate
  2. SAN sends out a wave of electrical activity across the walls of the atrium
  3. Contraction of the walls of the atrium
  4. Impulses from the atria are detected by the atrioventricular node where there is a short delay
  5. Impulses are then sent down the Bundle of His to the Purkinje fibres
  6. Electrical impulses spread from the base up the ventricular walls, causing simultaneous contraction of the ventricular walls
• Between the atria and the ventricles lies a fibrous band of non-connective tissue called the atrioventricular septum
• Myogenic means the contractions are stimulated by the heart
• The atrioventricular septum prevents the electrical wave crossing to the ventricles so they don't contract at the same time as the atria
• The delay before the ventricles contract is important because it allows the atria to finish contracting so blood can fill the ventricles
• The ventricles contract from the apex upwards because it pushed blood up and out of the arteries and it prevents blood from pooling in the apex
• Process of pressure receptors:

  1. High blood pressure
  2. Detected by pressure receptors in carotid arteries and aorta
  3. Impulses sent to the medulla increases frequency by parasympathetic neurones
  4. SAN decreases heart rate
  5. Decreases blood pressure
• Process of chemoreceptors:

  1. Increase in carbon dioxide concentration lowers pH
  2. Detected by chemoreceptors in carotid arteries
  3. Medulla increases frequency via sympathetic neurones
  4. SAN increases heart rate + contractions
  5. Carbon dioxide is pumped to lungs and excreted -> increases pH
• Changes in heart rate are controlled by the medulla oblongata
• Medulla contains an acceleratory and inhibitory centre
• The acceleratory and inhibitory centres are linked to SAN by sympathetic and parasympathetic neurones