3.6.1.3 control of heart rate

Question 1

Describe how a heartbeat is initiated and coordinated.

Answer 1

1. SAN sends wave of electrical activity causing atrial contraction.
2. Non-conducting tissue prevents immediate contraction of ventricles / prevents impulses reaching the ventricles;
3. AVN delays (impulse) whilst blood leaves atria / ventricles fill;
4. (AVN) sends wave of electrical activity / impulses down Bundle of His;
5. Causing ventricles to contract from base up;

Question 2

The sinoatrial node (SAN) is in the right atrium of the heart. Describe the role of the sinoatrial node.

Answer 2

Sends out electrical activity / impulses;
Initiates the heartbeat / acts as a pacemaker / (stimulates) contraction of atria;

Question 3

When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay.

Answer 3

Allow atria to empty / contract / ventricles to fill;

Before ventricles contract;

Question 4

Exercise increases HR, describe the role of receptors in controlling heart rate

Answer 4

Chemoreceptors detect a change in CO2

impusles sent to medulla/cardiac centre

more impulses to SAN

by sympathethic nerve