Control of heart rate

Control of heart rate by chemoreceptors and pressure receptors 

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Control of heart rate
The autonomic nervous system controls the involuntary action of internal muscles and glands. It has 2
divisions:
1. The sympathetic nervous system - this stimulates effectors and therefore speeds up any activity.
Helps us cope with stressful situations by heightening air awareness and preparing us for activity
(fight or flight response)
2. The parasympathetic nervous system - inhibits effectors and slows down any activity. Controls
activities under normal resting conditions; is concerned with conserving energy and replenishing the
body's reserves.
The actions of the sympathetic nervous system and the parasympathetic nervous system oppose one
another - they are antagonistic
Changes to the heart rate are controlled by the brain called the medulla oblongata. This has 2 centres:
o Centre that increases heart rate which is linked to the SAN by the sympathetic nervous system
o Centre which decreases heart rate which is linked to the SAN by the parasympathetic nervous
system
Control by chemoreceptors
Chemoreceptors are found in the walls of the carotid arteries (arteries that serve the brain). They are
sensitive to changes in the pH of the blood that results from changes in CO2 concentration (acidic).
1. When the blood has a higher than normal concentration of CO2 the pH is lowered
2. Chemoreceptors in the wall of the carotid arteries detect the change and increases the frequency of
nerve impulses to the medulla oblongata which increases the heart rate -> sympathetic nervous
system
3. Increased blood flow leads to more CO2 being removed from the blood by the lungs causing pH
levels to go back to normal
4. Chemoreceptors in the walls of the carotid arteries detect the change and reduces the frequency of
nerve impulses to the medulla oblongata which decreases the heart rate -> parasympathetic
nervous system
Control by pressure receptors
Pressure receptors occur within the walls of the carotid arteries and the aorta. They operate as follows:
o When blood pressure is higher than normal - pressure receptors send nervous impulse to the
medulla oblongata. Medulla oblongata sends nervous impulse via the parasympathetic nervous
system to the SAN to decrease heart rate
o When blood pressure is lower than normal - pressure receptors sends nervous impulse to the
medulla oblongata. Medulla oblongata send nervous impulse via the sympathetic nervous system
to the SAN to increase heart rate

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