3.6.1.3 Control of heart rate Flashcards
Why is heart muscle described as ‘myogenic’?
The heart muscle can contract and relax without receiving signals from the nerves.
What is the function of the bundles of His?
The bundle of His conduct waves of electrical activity between ventricles to the apex (bottom) of the heart.
Why do animals need to alter their heart rate?
Animals need to alter their heart rate to respond to internal stimuli.
Name the effectors that are involved in increasing or decreasing heart rate.
Cardiac muscles
Describe the function of the sinoatrial node.
[1 mark]
The sinoatrial node acts as a pacemaker/sets the rhythm of the heartbeat.
Describe the function of the Purkyne tissue.
[1 mark]
The Purkyne tissue conducts electrical impulses through the ventricle walls.
Exercise causes an increase in the levels of carbon dioxide in the blood.
Explain how increased blood CO₂ leads to an increased heart rate.
[4 marks]
- Chemoreceptors in the aorta/carotid artery/medulla detect the high CO₂ concentration.
- Impulses are sent from the receptors to the medulla,…
- …which sends impulses along sympathetic neurones to the sinoatrial node (SAN).
- These neurones secrete noradrenaline, which binds to receptors on the SAN.
- This increases the SAN activity, which increases heart rate.
Exercise causes an increase in the levels of carbon dioxide in the blood.
State two other chemical stimuli that cause the heart rate to increase during exercise.
[2 marks]
- Low blood O₂ level
- Low blood pH level
(The low blood pH is caused by the increased CO₂ level)
After undergoing AVN ablation, patients also need to have a pacemaker implanted.
Suggest why this is necessary.
[2 marks]
- Without a functioning AVN, the heart can’t beat normally/ventricles can’t contract normally.
- A pacemaker is needed to generate electrical impulses that cause the heart to beat normally/ventricles to contract normally.
