3.6.1.3 - Control of heart rate

Question 1

Cardiac muscle is myogenic. What does this mean?

Answer 1

It can contract and relax without receiving electrical impulses from nerves

Question 2

Describe the myogenic stimulation of the heart and transmission of a
subsequent wave of electrical activity

Answer 2

1) Sinoatrial node (SAN) acts as pacemaker → releases regular waves of electrical activity across atria
○ Causing atria to contract simultaneously

2) Non-conducting tissue between atria / ventricles prevents impulse passing directly to ventricles
○ Preventing immediate contraction of ventricles

3) Waves of electrical activity reach atrioventricular node (AVN) which delays impulse
○ Allowing atria to fully contract and empty before ventricles contract

4) AVN sends wave of electrical activity down bundle of His, conducting wave between ventricles to apex where it branches into Purkyne tissue
○ Causing ventricles to contract simultaneously from the base up

Question 3

Where are chemoreceptors and pressure receptors located?

Answer 3

Chemoreceptors and pressure receptors are located in the aorta and carotid arteries

Question 4

Describe the roles of chemoreceptors, pressure receptors, the autonomic nervous system and effectors in controlling heart rate
when there is a fall in blood pressure OR rise in blood CO2 conc. / fall in blood pH

Answer 4

1. Baroreceptors detect fall in blood
   pressure and / or chemoreceptors detect
   blood rise in blood CO2 conc. or fall in blood pH
2. They Send impulses to medulla / cardiac
   control centre
3. Which send more frequent impulses to
   SAN along sympathetic neurones
4. So more frequent impulses sent
   from SAN and to / from AVN
5. So cardiac muscle contracts more frequently
6. So heart rate increases

Question 5

Describe the roles of chemoreceptors, pressure receptors, the autonomic
nervous system and effectors in controlling heart rate when there is a rise in blood pressure OR fall in blood CO2 conc. / rise in blood pH

Answer 5

1. Baroreceptors detect rise in blood
   pressure and / or chemoreceptors detect
   fall in blood CO2 conc. or rise in blood pH
2. they Send impulses to medulla / cardiac
   control centre
3. Which send more frequent impulses to
   SAN along parasympathetic neurones
4. So less frequent impulses sent
   from SAN and to / from AVN
5. So cardiac muscle contracts less
   frequently
6. So heart rate decreases