Control of heart rate

Question 1

Explain the control of the heart rate

Answer 1

1. Sinoatrial node will release a wave of depolarisation across the atria causing it to contract.
2. The non-conductive tissue between the atria and the ventricles will prevent the impulse from reaching the ventricles
3. The atrioventricular node delays the impulse so the ventricles can fill with blood.
4. The atrioventricular node sends a wave of depolarisation down the Bundle of His which causes ventricles to contract from the bottom up

Question 2

Which part of the brain controls the heart rate via what system?

Answer 2

Medulla oblongata in the brain controls the heart rate via the autonomic nervous system

Question 3

Which 2 systems increase and decrease heart rate?

Answer 3

Sympathetic nervous sytem - increases heart rate
Parasympathetic nervous system - decreases heart rate

Question 4

Which receptors respond to change in pH and blood pressure?

Answer 4

Chemoreceptors - pH
Baroreceptors - pressure

Question 5

What happens if blood pressure increases?

Answer 5

1. Baroreceptors in walls of aorta and carotid artery are stretched due to high blood pressure
2. More electrical impulses are sent to medulla oblongata. More impulses are sent to the sinoatrial node via the parasympathetic nervous system to decrease the frequency of electrical impulses
3. This means the SAN releases fewer impulses hence reduced heart rate.

Question 6

What happens if blood pressure decreases

Answer 6

1. Baroreceptors in walls of aorta and carotid artery are not stretched due to low blood pressure
2. More electrical impulses are sent to medulla oblongata. More impulses are sent to the sinoatrial node via the sympathetic nervous system to increases the frequency of electrical impulses
3. This means the SAN releases more impulses hence increases heart rate.

Question 7

What happens if pH decreases

Answer 7

1. Chemoreceptor in wall of aorta and carotid artery detect the decrease in pH caused by CO2
2. More impulses sent to medulla oblongata. More impulses sent to SAN via sympathetic nervous system to increase frequency of electrical impulses
3. Increased heart rate delivers blood to lungs to remove CO2