14.5 control of heart rate

Question 1

what does the sympathetic nervous system do?

Answer 1

speeds up activity

Question 2

what is the relationship between sympathetic & parasympathetic nervous systems?

Answer 2

antagonistic

Question 3

what does the parasympathetic nervous system do?

Answer 3

inhibits effectors

Question 4

what does it mean that heart rate is myogenic?

Answer 4

contraction is initiated by muscles itself

Question 5

describe how heart rate is controlled in its resting state. (4)

Answer 5

1- SAN (sinatrial node) produces wave of electrical impulse to both atria & causes it to contract
2- action potential reaches AVN (atrioventricular node) which delays the impulse from reaching the ventricles
3- AVN conveys the impulse down the bundle of his & releases it at the apex
4- ventricles contract from the apex upwards

Question 6

what are chemoreceptors in the heart sensitive to?

Answer 6

pH

Question 7

describe how the heart rate is controlled by chemoreceptors. (6)

Answer 7

1- high [CO2] decreases pH
2- chemoreceptors in the walls of carotid arteries & aorta detects change in pH
-> increases frequency of nervous impulses to the centre of medulla oblongata to increase heart rate
3- higher frequency of impulses are sent through the sympathetic nervous system to the sinoatrial node (SAN) to increase heart rate
4- higher blood flow leads to more CO2 being removed from the lungs & decreases [CO2]
5- chemoreceptors detects change in pH and decreases frequency of nerve impulses to the centre of medulla oblongata
6- medulla oblongata decreases frequency of impulses to the sinoatrial node

Question 8

where are pressure receptors located?

Answer 8

walls of carotid arteries & the aorta

Question 9

how does pressure receptors control heart rate in low blood pressure?

Answer 9

• pressure receptors transmit more impulses to the centre in medulla oblongata -> impulses sent through parasympathetic nervous system to SAN & heart rate decreases

Question 10

how does pressure receptors control heart rate in high blood pressure?

Answer 10

• pressure receptors transmit less impulses to the centre in medulla oblongata -> impulses sent through sympathetic nervous system to SAN & heart rate increases