14 More On Control Of Heart Rate

Question 1

Control by chemoreceptors

Answer 1

When blood had higher than norm conc of CO2 pH lowered.
Chemoreceptors in wall of carotid arteries and aorta detect this, increase freq of nervous impulses to centre in medulla oblongata that increases heart rate.
Centre increases freq of impulses via sympathetic nervous system to SAN, this in turn increases rate of production of electrical waves by SAN and so increases heart rate.
Increases blood flow this causes leads to more CO2 removed by lungs and so CO2 conc of blood returns to normal.
Ph of blood rises to normal, chemoreceptors in wall of carotid arteries and aorta reduce freq of nervous impulses to medulla oblongata.
Medulla oblongata reduces freq of impulses to SAN therefore reduction in heart rate

Question 2

Control by pressure receptors when blood pressure higher than norm

Answer 2

Pressure receptors transmit more nervous impulses to centre in medulla oblongata that decreases heart rate
Centre sends impulses via parasympathetic nervous system to SAN of heart, leading to decrease in rate at which heart beats

Question 3

When blood pressure lower than norm

Answer 3

Pressure receptors transmute more nervous impulses to centre in medulla oblongata that increases heart rate
Centre sends impulses via sympathetic nervous system to SAN which increases rate at which heart beats