Control of heart rate

• divisions of autonomic nervous system

  sympathetic and parasympathetic
• sympathetic nervous system

  the division of the autonomic nervous system that stimulates effectors and speeds up activity
• parasympathetic nervous system

  the division of the autonomic nervous system that inhibits effectors and slows activity
• why is the heart is myogenic?

  The capacity of the heart to generate its own electrical impulse, which causes the cardiac muscle to contract.
• what and where is the sinoatrial node?

  pacemaker in right atrium
• Heart beat process

  1. wave of electrical excitation spreads out from the sinoatrial node across both atria causing a contraction

  2) layer of non conductive tissue prevents wave crossing to ventricles

  3) wave enters atrioventricular node which after a short delay coveys a wave along a series of muscle fibres called purkyne tissue which make up a structure called the bundle of His

  4) wave is carries to the base of the ventricles cashing a contraction from the apex upwards
• what controls changes to heart rate ?

  medulla oblongata
• Decreased blood pH response

  1. When the blood has a higher than normal concentration of carbon dioxide, its pH is lowered.

  2) The chemoreceptors in the wall of the arteries detect this and increase the frequency of nervous impulses to the centre of the medulla oblongata that increases heart rate.

  3) This centre increases the frequency of impulses via the sympathetic nervous system to the sinoatrial node. This, in turn, increases the rate of production of electrical waves by the sinoatrial node and therefore increases the heart rate

  .4) The increased blood flow that this causes leads to more carbon dioxide being removed by the lungs

  5) As a consequence the pH of the blood rises to normal and the chemoreceptors reduce the frequency of nerve impulses to the medulla oblongata

  .6)The medulla oblongata reduces the frequency of impulses to the sinoatrial node, which therefore leads to a reduction in the heart rate.
• when blood pressure is higher than normal

  pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that decreases heart rate. This centre sends impulses via the parasympathetic nervous system to the sinoatrial node of the heart, which leads to a decrease in the rate at which the heart beats
• when blood pressure is lower than normal

  When blood pressure is lower than normal, pressure receptors transmit more nervous impulses to the centre in the medulla oblongata that increases heart rate. This centre sends impulses via the sympathetic nervous system to the sinoatrial node, which increases the rate at which the heart beats.