3.6.1.3 Control of heart rate

Question 1

Cardiac conduction system

Answer 1

sino-atrial node (SAN)
atrio-ventricular node (AVN)
bundle of his
Bundle branches
Purkinje Fibre

Question 2

The heart’s control process

Answer 2

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

Question 3

autonomic nervous system
general

Answer 3

• Controls involuntary unconscious activities such as heart rate
• part of the motor nervous system
• 2 division (Sympathetic neurones and Parasympathetic neurones)
• work antagonistically (opposite)

Question 4

how autonomic neuron control heart rate process

Answer 4

1. Sensory inputs from chemical and pressure receptors in blood vessels
2. Control centre - 2 areas Medulla oblongata (brain stem)
3. The sympathetic neurones increase the force and rate of contraction.
   The parasympathetic neurones decrease the heart rate.

Question 5

chemoreceptor control heart rate

Answer 5

During exercise, respiration in muscles increases

Carbon dioxide levels in the blood increases, pH decreases

Chemoreceptors detect the change and send impulses to medulla oblongata

Medulla increases frequency of impulses through the sympathetic nerve to the SAN in the heart

SAN increases heart rate

More blood flows through the lungs allowing more carbon dioxide to be excreted and raising blood pH back to set point.

Question 6

Pressure receptor (Baroreceptor) control heart rate

Answer 6

When blood pressure is higher than normal

Baroreceptors detect the change and send impulses to the medulla

Medulla increases frequency of impulses through the parasympathetic nerve to the SAN in the heart

SAN decreases heart rate

Heart rate and blood pressure decreases.

if its low, sent to sympathetic, cause increase

1. pressure receptor
2. send impulse to cardiovascular center
3. impulse via parasympathetic nerves to SAN
4. decrease impulse from SAN
   decrease impulse to AVN

Question 7

some drugs inhibit the transmission of nerve impulse to th eheart. Exaplain howt these drugs reduce high blood pressure

Answer 7

inhibit impulse in sympathetic nerves
SAN not stimulated