9.3 1 control of heart rate

Maintenance of a state of dynamic equilibrium through the response of the body to internal and external stimuli

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 volume x heart rate = cardiac output

By autonomic (involuntary ) nervous system

Situated in the medulla oblongata of the brain: changes in heart rate and volume pumped per beat

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

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

release acetylcholine inhibiting the SAN and slowing the heart down - targets the SAN

Found in the sinuses of carotid arteries in neck and aorta Heart rate during excercise

Baroreceptors send a steady stream of signals back to sensory neurones to cardiac centre in the brain

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

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

Walls of aorta and carotid arteries Sensitive to level of carbon dioxide in the blood

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

Chemoreceptors reduce number of impulses in the sympathetic nerve to heart and reduces the acceleration of the heart so it returns to intrinsic rhythm

The control of breathing rate

Sympathetic nerve stimulates the adrenal medulla to release hormone adrenaline carried around the blood and binds to target organs include the SAN Stimulates also cardiac centre in brain increasing sympathetic neurones supplying the heart increase heart rate Supplys extra oxygen and glucose

Impulses from the cardiac centre travel to other effectors as well as the heart

Fewer impulses are sent along sympathetic nerves to may blood vessels causing smooth lining the vessels to contract narrowing and closing the vessels Blood flow diverted from temporarily less important areas

Involuntary Intense

Relaxes Involuntary

Stays relatively constant