9.8 - control of heart rate in mammals

Question 1

SAN pacemaker controlling heart rate

Answer 1

• SAN is stimulated
• impulse sent through walls of atria causing them to contract
• impulse reaches AVN
• impulse travels down Bundle of His
• impulse travels through purkinje fibres causing walls of ventricle to contract
• blood is forced through arteries & out the heart

Question 2

what are baroreceptors

Answer 2

• pressure receptors in the wall of aorta and carotid arteries that are sensitive to blood pressure
• these can send impulses to medulla oblangata to control b.p.

Question 3

what are chemoreceptors?

Answer 3

• pH receptors in wall of aorta and carotid arteries that detect carbon dioxide concentration of blood
• send impulses to medulla oblangata so that a constant blood pH can be maintained

Question 4

what is the cardiac centre

Answer 4

• located in medulla oblangata
• controls HR and b.p. through hormones and nerve impulses

Question 5

responses to changes in blood pH and blood pressure

what happens when blood pH falls

Answer 5

• chemoreceptors
• nerve impulses sent to cardiac centre
• increase in impulses in sympathetic nerve to SAN releases noroadrenaline
• SAN depolarises more frequently
• SAN stimulates heart rate increase so CO2 lost faster in lungs
• blood pH rises to normal

Question 6

responses to changes in blood pH and blood pressure

what happens when blood pH rises

Answer 6

• detected by chemoreceptors
• nerve impulses sent to cardiac centre
• increase in impulses in parasympathetic nerve to SAN releases ACh
• SAN depolarises less frequently
• heart rate slows
• blood pH falls to normal

Question 7

responses to changes in blood pH and blood pressure

what happens when blood pressure falls

Answer 7

• detected by baroreceptors
• nerve impulses sent to cardiac centre
• increase in impulses in sympathetic nerve to SAN releases noroadrenaline
• SAN depolarises more frequently
• heart stroke volume increases so blood pressure increases

Question 8

responses to changes in blood pH and blood pressure

what happens when blood pressure increases

Answer 8

• detected by baroreceptors
• nerve impulses sent to cardiac centre in medulla oblangata
• increase in impulses in parasympathetic nerve to SAN releases ACh
• SAN depolarises less frequently
• heart stroke volume falls so b.p. is reduced

Question 9

effect of adrenaline on heart rate

Answer 9

• stress or shock (fight/flight) response can cause the CNS to stimulate the adrenal medulla

Question 10

effect of adrenaline on heart rate - how?

Answer 10

• increased frequency of nerve impulses in a branch of the sympathetic autonomic nervous system
• adrenaline released which then ciruclated in the blood
• adrenaline affects target cells in cardiac centre and in the SAN
• increased heart rate to prepare body for increased activity