3.6.1.3 Control of heart rate

Question 1

What initiates the myogenic stimulation of the heart?

Answer 1

The sinoatrial node (SAN) initiates the myogenic stimulation of the heart.

Question 2

Where is the sinoatrial node (SAN) located?

Answer 2

The SAN is located in the wall of the right atrium of the heart.

Question 3

What is the function of the SAN?

Answer 3

The SAN acts as the heart’s pacemaker by generating electrical impulses that initiate contraction.

Question 4

What happens after the electrical impulse is generated by the SAN?

Answer 4

The electrical impulse spreads across the walls of the atria, causing atrial contraction.

Question 5

Why does the electrical impulse not directly pass to the ventricles?

Answer 5

A layer of non-conductive tissue between the atria and ventricles prevents direct transmission of the electrical impulse.

Question 6

What structure delays the electrical impulse after it spreads from the SAN?

Answer 6

The atrioventricular node (AVN) delays the electrical impulse.

Question 7

Why is there a delay at the AVN?

Answer 7

The delay at the AVN allows time for the atria to fully contract and empty their blood into the ventricles before ventricular contraction begins.

Question 8

Where is the AVN located?

Answer 8

The AVN is located in the lower part of the right atrium near the septum.

Question 9

What happens after the delay at the AVN?

Answer 9

The electrical impulse is transmitted along the Purkyne tissue in the bundle of His.

Question 10

What is the role of the Purkyne tissue?

Answer 10

The Purkyne tissue conducts the electrical impulse to the apex of the heart and then upwards along the walls of the ventricles.

Question 11

What is the result of the electrical impulse reaching the ventricular walls?

Answer 11

The ventricles contract from the apex upwards, ensuring efficient blood ejection.

Question 12

What do chemoreceptors detect?

Answer 12

Chemoreceptors detect changes in blood pH, which are caused by changes in carbon dioxide levels.

Question 13

Where are chemoreceptors located?

Answer 13

Chemoreceptors are located in the carotid bodies and aortic bodies.

Question 14

What happens when chemoreceptors detect a high level of carbon dioxide?

Answer 14

The chemoreceptors send impulses to the medulla oblongata, which increases the frequency of impulses via the sympathetic nervous system to the SAN.

Question 15

What effect does increased sympathetic stimulation have on heart rate?

Answer 15

Increased sympathetic stimulation increases heart rate.

Question 16

What do pressure receptors (baroreceptors) detect?

Answer 16

Pressure receptors detect changes in blood pressure.

Question 17

Where are pressure receptors located?

Answer 17

Pressure receptors are located in the walls of the carotid arteries and the aorta.

Question 18

What happens when blood pressure is too high?

Answer 18

Pressure receptors send impulses to the medulla oblongata, which increases parasympathetic nervous activity to the SAN.

Question 19

What effect does increased parasympathetic stimulation have on heart rate?

Answer 19

Increased parasympathetic stimulation decreases heart rate.

Question 20

Which part of the autonomic nervous system decreases heart rate?

Answer 20

The parasympathetic nervous system decreases heart rate.

Question 21

Which part of the autonomic nervous system increases heart rate?

Answer 21

The sympathetic nervous system increases heart rate.

Question 22

What are the effectors involved in controlling heart rate?

Answer 22

The effectors are the cardiac muscles, which respond to autonomic nervous system impulses by adjusting the rate and force of contraction.

Question 23

Describe the role of receptors and of the nervous system in exercise. (4)

Answer 23

1. Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid / fall in pH
   OR
   Baro / pressure receptors detect rise in blood pressure;
2. Send impulses to cardiac centre / medulla;
3. More impulses to SAN;
4. By sympathetic (nervous system for chemoreceptors / CO2)
   OR
   By parasympathetic (nervous system for baro / pressure receptors / blood pressure);

Question 24

How do both ventricles contract simultaneously after the heartbeat is initiated by the SAN? (2)

Answer 24

1. Electrical activity only through Bundle of His / AVN;
2. Wave of electrical activity passes over / through both ventricles at the
   same time;

Question 25

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 25

1. Electrical activity only through Bundle of His / AVN;
2. Wave of electrical activity passes over / through both ventricles at the same time;

Question 26

Describe how a heartbeat is initiated and coordinated.

Answer 26

1. SAN sends wave of electrical activity / impulses (across atria) causing atrial contraction; Accept excitation
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;
   Allow Purkyne fibres / tissue
5. Causing ventricles to contract from base up;

Question 27

The heart controls and coordinates the regular contraction of the atria and ventricles.

Describe how.

Answer 27

1. SAN → AVN → bundle of His / Purkyne fibres;
2. Mark for correct sequence
3. Impulses / electrical activity (over atria);
4. Atria contract;
5. Non-conducting tissue (between atria and ventricles);
6. Delay (at AVN) ensures atria empty / ventricles fill before ventricles contract;
7. Ventricles contract from apex upwards;

Question 28

The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN). Describe how.

Answer 28

1. SAN initiates heartbeat / acts as a pacemaker / myogenic; Q Must be in context
2. (SAN) sends wave of electrical activity / impulses (across atria) causing atrial contraction; Reject: signals / electronic / messages / nerve impulses once only
3. AVN delays (electrical activity / impulses); Neutral: reference to non-conducting tissue delaying impulses instead of the AVN
4. (Allowing) atria to empty before ventricles contract / ventricles to fill before they contract;
5. (AVN) sends wave of electrical activity / impulses down Bundle of His / Purkyne fibres;
6. (Causing) ventricles to contract (from base up) / ventricular systole