3.6.1.3 Control of heart rate (Unit 6 Responding to Environment)

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

Question 5

Describe how the heart beat is controlled

Answer 5

Sino Atrial Node initiates a wave of electrical impulses across both atria causing them to contract
Non-conductive tissue prevents impulse going straight to ventricle
Atrio Ventricular Node delay impulse so ventricles can fill
AV Node sends wave of electrical impulses down Bundle of His
Ventricles contract from bottom up.

Question 6

When CO2 increases, how does the cardiac system respond?

Answer 6

pH in blood lowers
Chemoreceptors detect it
CO2 needs to be removed
Sensory neurone takes more impulses to medulla
Medulla sends more impulses along the sympathetic nerve
Sympathetic nerve causes SAN to increase
Heart rate increases

Question 7

When CO2 decreases, how does the cardiac system respond?

Answer 7

pH in blood increases
Chemoreceptors detect it
Sensory neurone takes more impulses to medulla
Medulla sends more impulses along the parasympathetic nerve
Parasympathetic nerve causes SAN to decrease
Heart rate decreases

Question 8

When blood pressure increases, how does the cardiac system respond?

Answer 8

Baroreceptors detect pressure increase
Too high pressure can damage artery walls, so needs to be restored
Sensory neurone takes more impulses to medulla
Medulla sends more impulses along the parasympathetic nerve
parasympathetic nerve causes SAN to decrease
Heart rate decreases

Question 9

When blood pressure decreases, how does the cardiac system respond?

Answer 9

Baroreceptors detect pressure increase
Too low pressure means not enough oxygen etc. will get to cells
Sensory neurone takes more impulses to medulla
Medulla sends more impulses along the sympathetic nerve
sympathetic nerve causes SAN to increase
Heart rate increases