3.6.1.3 Control of heart rate Flashcards
What initiates the myogenic stimulation of the heart?
The sinoatrial node (SAN) initiates the myogenic stimulation of the heart.
Where is the sinoatrial node (SAN) located?
The SAN is located in the wall of the right atrium of the heart.
What is the function of the SAN?
The SAN acts as the heart’s pacemaker by generating electrical impulses that initiate contraction.
What happens after the electrical impulse is generated by the SAN?
The electrical impulse spreads across the walls of the atria, causing atrial contraction.
Why does the electrical impulse not directly pass to the ventricles?
A layer of non-conductive tissue between the atria and ventricles prevents direct transmission of the electrical impulse.
What structure delays the electrical impulse after it spreads from the SAN?
The atrioventricular node (AVN) delays the electrical impulse.
Why is there a delay at the AVN?
The delay at the AVN allows time for the atria to fully contract and empty their blood into the ventricles before ventricular contraction begins.
Where is the AVN located?
The AVN is located in the lower part of the right atrium near the septum.
What happens after the delay at the AVN?
The electrical impulse is transmitted along the Purkyne tissue in the bundle of His.
What is the role of the Purkyne tissue?
The Purkyne tissue conducts the electrical impulse to the apex of the heart and then upwards along the walls of the ventricles.
What is the result of the electrical impulse reaching the ventricular walls?
The ventricles contract from the apex upwards, ensuring efficient blood ejection.
What do chemoreceptors detect?
Chemoreceptors detect changes in blood pH, which are caused by changes in carbon dioxide levels.
Where are chemoreceptors located?
Chemoreceptors are located in the carotid bodies and aortic bodies.
What happens when chemoreceptors detect a high level of carbon dioxide?
The chemoreceptors send impulses to the medulla oblongata, which increases the frequency of impulses via the sympathetic nervous system to the SAN.
What effect does increased sympathetic stimulation have on heart rate?
Increased sympathetic stimulation increases heart rate.
What do pressure receptors (baroreceptors) detect?
Pressure receptors detect changes in blood pressure.
Where are pressure receptors located?
Pressure receptors are located in the walls of the carotid arteries and the aorta.
What happens when blood pressure is too high?
Pressure receptors send impulses to the medulla oblongata, which increases parasympathetic nervous activity to the SAN.
What effect does increased parasympathetic stimulation have on heart rate?
Increased parasympathetic stimulation decreases heart rate.
Which part of the autonomic nervous system decreases heart rate?
The parasympathetic nervous system decreases heart rate.
Which part of the autonomic nervous system increases heart rate?
The sympathetic nervous system increases heart rate.
What are the effectors involved in controlling heart rate?
The effectors are the cardiac muscles, which respond to autonomic nervous system impulses by adjusting the rate and force of contraction.
Describe the role of receptors and of the nervous system in exercise. (4)
- Chemoreceptors detect rise in CO2 / H+ / acidity / carbonic acid / fall in pH
OR
Baro / pressure receptors detect rise in blood pressure; - Send impulses to cardiac centre / medulla;
- More impulses to SAN;
- By sympathetic (nervous system for chemoreceptors / CO2)
OR
By parasympathetic (nervous system for baro / pressure receptors / blood pressure);
How do both ventricles contract simultaneously after the heartbeat is initiated by the SAN? (2)
- Electrical activity only through Bundle of His / AVN;
- Wave of electrical activity passes over / through both ventricles at the
same time;
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.
- Electrical activity only through Bundle of His / AVN;
- Wave of electrical activity passes over / through both ventricles at the same time;
Describe how a heartbeat is initiated and coordinated.
- SAN sends wave of electrical activity / impulses (across atria) causing atrial contraction; Accept excitation
- Non-conducting tissue prevents immediate contraction of ventricles / prevents impulses reaching the ventricles;
- AVN delays (impulse) whilst blood leaves atria / ventricles fill;
- (AVN) sends wave of electrical activity / impulses down Bundle of His;
Allow Purkyne fibres / tissue - Causing ventricles to contract from base up;
The heart controls and coordinates the regular contraction of the atria and ventricles.
Describe how.
- SAN → AVN → bundle of His / Purkyne fibres;
- Mark for correct sequence
- Impulses / electrical activity (over atria);
- Atria contract;
- Non-conducting tissue (between atria and ventricles);
- Delay (at AVN) ensures atria empty / ventricles fill before ventricles contract;
- Ventricles contract from apex upwards;
The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN). Describe how.
- SAN initiates heartbeat / acts as a pacemaker / myogenic; Q Must be in context
- (SAN) sends wave of electrical activity / impulses (across atria) causing atrial contraction; Reject: signals / electronic / messages / nerve impulses once only
- AVN delays (electrical activity / impulses); Neutral: reference to non-conducting tissue delaying impulses instead of the AVN
- (Allowing) atria to empty before ventricles contract / ventricles to fill before they contract;
- (AVN) sends wave of electrical activity / impulses down Bundle of His / Purkyne fibres;
- (Causing) ventricles to contract (from base up) / ventricular systole
