9.8 - Control of heart rate in mammals

Question 1

What changes in the blood does the heart respond to?

Answer 1

CO2 concentration -detected by chemoreceptors in the aorta and carotid arteries

Blood pressure -detected by baroreceptors in aorta and carotid arteries

Question 2

Where do receptors for heart rate send impulses to?

Answer 2

The medulla oblongata where the cardiac control centre is located

Question 3

What Is the role of chemoreceptors?

Answer 3

• in walls of aorta + carotid artieries
• DETECT CO2 LEVELS & involved controlling breathing
• as they increase, blood pH decreases, CRs detect this + send impulse to CCC
• CCC increase impulse travelling down sump nerve to heart - HR increases - increased blood flow - COs removed
• as CO2 decreases, blood pH increases
• CRs reduce no impulses to CCC
• CCC sends less impulses down sympathetic nerve - HR decreases - returns to intrinsic rhythm
  Impulses are passed down sympathetic nerves from the acceleratory centre of the cardiac centre to the SAN causes an increase in heart rate by releasing noradrenaline

Question 4

How is heart rate decreased?

Answer 4

Impulses are passed down parasympathetic nerves and release acetylcholine, inhibiting SAN and slowing HR

Question 5

how is heart rate increased?

Answer 5

• nerve impulses travel down sympathetic nerve from cardiac centre in brain to heart
• release noradrenaline to stimulate SAN
• this increases freq of signals from pacemaker region - heart beats more quickly
• branches of sympathetic nerve also pass into ventricles - increase contraction force

Question 6

what is the role of baroreceptors

Answer 6

• found in sinuses of carotid arteries on neck + aorta
• CONTROLLING HR DURING EXERCISE
• at rest - send steady stream of signals back thru sensory neuters to cardiac centre
• when exercise start - blood vessels dilate (vasodilation) in response to hormone adrenaline + BP falls little
• BP falling reduced stretch on baroreceptors and they almost stop responding but CCC sends signals along symp nerve to stimulate HR + increase BP by vasoconstriction
• when ex stops - BP in arteries increase + heart pumping blood faster than necessary - so baroreceptors = stretched
• BRs respond by sending more impulse to CCC and CCC then sens impulse thru para nerve to slow HR + vasodilation to occur -> lowers bp

Question 7

what is the role of the autonomic nervous system in causing the release
of adrenaline to increase heart rate.

Answer 7

• when stressed - sympathetic nerve stimulates adrenal medulla to release hormone adrenaline
• adr is carried around body in blood + binds to receptors in target organs inc SAN
• adr stimulates CCC - increase impulses in sympathetic neurones supplying heart + has direct effect on SAN (increase HR)
• supplys u w extra O2 + glucose in case needed to fight/flight