Heart

• Parasympathetic system


  Decreases heart rate and constriction of pupils
• Autonomic nervous system consists of sympathetic and parasympathetic systems


  Antagonistic systems with opposing effects
• Disturbance in equilibrium between sympathetic and parasympathetic systems

  Generates a response by the effector
• Bundle of His branches into Purkyne fibres which carry the wave upwards, causing ventricles to contract and empty
• Sympathetic system

  Increases heart rate and dilation of pupils
• Sinoatrial node in the right atrium is the pacemaker of the heart, initiating a wave of electrical stimulation
• Ventricles start contracting after atria due to tissue at the base of the atria
• Heart is myogenic due to its ability to initiate its own contraction
• Electrical wave passes from atrioventricular node to ventricles, down the bundle of His to the apex of the heart
• Sinoatrial node connected to nerves from the medulla oblongata

  Accelerator nerve delivers higher frequency of impulses to increase heart rate, vagus nerve delivers slower frequency of impulses to decrease heart rate
• Factors which increase the heart rate

  • Low pH caused by high carbon dioxide concentration
  • Stretch receptors responding to muscle movement
  • Decrease in blood pressure
  • Adrenaline released to stimulate the fight or flight response
• Heart rate is decreased when

  pH increases as a result of decrease in carbon dioxide concentration and increase in blood pressure
• Accelerator nerve

  Delivers a higher frequency of impulses to the SAN to increase the heart rate
• Vagus nerve


  Delivers a slower frequency of impulses to slow down the heart rate