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Heart rate needs to be altered to meet varying demands of oxygen.
Controlled by a region of the brain called the medulla oblongata.
The medulla oblongata has two centres:
1. Centre which increases heart rate = linked to sinoatrial node by sympathetic nervous
2. Centre which decreases heart rate = linked to sinoatrial node by the parasympathetic
CHEMICAL and PRESSURE changes in the blood stimulate parts of the brain via
o Found in the wall of the carotid arteries.
o They are sensitive to pH changes that results from CO2 concentration changes
(exercise is a cause of increased CO2)
o When the chemoreceptors detect this change they increase the frequency of nerve
impulses to the medulla oblongata
o This centre increases impulse frequency via the sympathetic nervous system to the
sinoatrial node of the heart increased heart rate.
o The increases blood flow increases amount of CO2 removed at the lungs and therefore
pH returns to normal.
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The chemoreceptors detect the change and reduce the impulse frequency back to
Control by pressure receptors
o Found in the wall of the carotid arteries and the aorta.
o When blood pressure is higher than normal they send nervous impulse to the
medulla oblongata which decreases heart rate by sending impulses via the
parasympathetic nervous system to the sinoatrial node of the heart lowering the
pressure back to normal.…read more