Unit 6 Control Of Heart Rate

Question 1

Describe the role of receptors and of the nervous system in increasing of heart rate

Answer 1

1. Chemoreceptors detect rise in CO2, H and fall in ph
2. Send impulses to cardiac centre
3. More impulses to SAN
4. By sympathetic nervous system

Question 2

When the heart beats, both ventricles contract at the same time. Explain how this is coordinated in the heart after initiation of the heartbeat by the SAN

Answer 2

1. Electrical activity only through bundle of HIS/AVN
2. wave of electrical activity passes through both ventricles contract at the same time to contract upwards towards the matrix

Question 3

Describe how a heartbeat is initiated and coordinated

Answer 3

1. SAN sends wave of electrical activity causing atrial contraction
2. Non-conducting collagen tissues prevents immediate contraction of ventricles
3. AVN delays impulses whilst blood drains from atria
4. AVN sends wave of electrical impulses down the bundle of HIS and purkyne fibres
   5.causing ventricles to contract from base upwards towards the matrix

Question 4

The heart controls and coordinates the regular contraction of the atria and ventricles describe how

Answer 4

1. SAN to bundle of HIS and purkyne fibres
2. Impulses sent to the atria
3. Atria contracts
4. Non-conducting tissues
5. Delay at the AVN to allow the atria to contract and ventricles to fill up before contraction
6. Ventricles contract upwards towards the apex

Question 5

The cardiac cycle is controlled by the SAN and AVN

Answer 5

1. SAN initiates heartbeat and acts as a pacemaker
2. SAN sends a wave of electrical impulses causing atrial contraction
3. Allows atria to empty before ventricles contract
4. AVN sends wave of electrical activity down purkyne fibres and bundle of HIS
5. Causing ventricles to contract upwards towards the matrix