9.3 1 control of heart rate Flashcards
Homeostasis
Maintenance of a state of dynamic equilibrium through the response of the body to internal and external stimuli
Intrinsic rhythm of the heart
Is controlled by impulses initiated in the sinoatrial node and the spreads to the atrioventricular node and bundle of His to give a regular coordinated heart beat
NOT SUFFICIENT ENOUGH TO COPE WITH CHANGES IN DEMAND
Cardiac output
Cardiac volume x heart rate = cardiac output
Most nervous control of heart
By autonomic (involuntary ) nervous system
The cardiac control centre
Situated in the medulla oblongata of the brain: changes in heart rate and volume pumped per beat
Process
Chemical , stretch and pressure receptors in lining of the blood vessels and chambers of the heart send nerve impulses to the cardiac centre . It then responds by sending impulses to the heart along the parasympathetic and sympathetic nerves giving a fine level of control o pi ooo
Nerve impulses travelling down the sympathetic nerve
From cardiac centre
To the heart release noradrenaline to stimulate the SAN
Increase signals from the pacemaker region so that the heart beats more quickly
Branches of this sympathetic nerve also go into the ventricles so increase force of contraction
Nerve impulses along parasympathetic nerve
release acetylcholine inhibiting the SAN and slowing the heart down - targets the SAN
Baroreceptors
Found in the sinuses of carotid arteries in neck and aorta
Heart rate during excercise
At rest
Baroreceptors send a steady stream of signals back to sensory neurones to cardiac centre in the brain
When excercise starts
Blood vessels dilate (vasodilation) in response to the hormone adrenaline which is released in the anticipation of exercise and blood pressure falls a little
Reduces stretch on baroreceptors reduced stimulation
Cardiac control centre sends signal along the sympathetic nerve to stimulate the heart rate and increase blood pressure agin by vasoconstriction
When excercise stops
blood pressure in arteries increase as heart pumps harder and faster than it needs to so baroreceptors are stretched
Sending more sensory nerve signals to cardiac centre that sends impulses through parasympathetic system to slow down heart rate and widening of blood vessels
Chemoreceptors
Walls of aorta and carotid arteries
Sensitive to level of carbon dioxide in the blood
As carbon dioxide levels go up
pH of the blood goes down detected by the aortic and carotid chemoreceptors
Send impulses along sensory neurones to the cardiac control centre in medulla and this increases impulses travelling down the sympathetic nerve to the heart
Heart rate increase giving increased blood flow the lungs and more carbon dioxide is removed from the blood
Decrease in carbon dioxide levels
Chemoreceptors reduce number of impulses in the sympathetic nerve to heart and reduces the acceleration of the heart so it returns to intrinsic rhythm
