Regulation of Stoke Volume and Heart Rate

Question 1

Stimulation by sympathetic nerves has what effect on heart rate?

Answer 1

Heart rate increases.

Question 2

How do sympathetic nerves stimulate the heart rate?

Answer 2

• release noradrenaline
• acts of beta one receptors on the sinoatrial node
• increases slope of the pacemaker potential (increases rate of depolarisation)
• increases HR - tachycardia?

Question 3

Stimulation by parasympathetic nerves has what effect on heart rate?

Answer 3

Heart rate decreases.

Question 4

How do parasympathetic nerves stimulate the heart rate?

Answer 4

• release acetylcholine
• acts on muscarinic receptors on the sinoatrial node
• hyperpolarises cell and decreases slope of pacemaker potential (decreases rate of depolarisation)
• decreases HR - bradycardia?

Question 5

Define Starling’s law.

Answer 5

The energy of contraction is proportional to the initial length of the cardiac muscle fibre, ie. preload.

• preload is affected by end distolic volume

Question 6

Describe, in detail, what an increase in total resistance would do to stoke volume.

Answer 6

• if total peripheral resistance increases,
• aortic pressure will increase
• the ventricle will have to work harder to push open the aortic valve
• and it will have less energy to eject the blood
• therefore, stroke volume will decrease

Question 7

What effect does sympathetic innervation have on stroke volume?

Answer 7

• release of noradrenaline
• acts on beta one receptors on the myocytes
• increases contractility (an ionotropic effect)
• gives a stonger but shorter contraction

Question 8

What effect does parasympathetic innervation have on stoke volume?

Answer 8

• gives little effect

- probably because the vagus nerve does not innervate the ventricular muscle