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

Label the sinoatrial node (SAN), atrioventricular node (AVN), Bundle of His
and Purkyne tissue on a diagram of the heart

Answer 2

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Question 3

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

Answer 3

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 4

Where are chemoreceptors and pressure receptors located?

Answer 4

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

Question 5

Describe the roles of chemoreceptors, pressure receptors, the autonomic
nervous system and effectors in controlling heart rate

Answer 5

Sypathetic Nerve :

1. Baroreceptors detect fall in blood
   pressure or chemoreceptors detect
   blood rise in blood CO2 conc. or fall in blood pH
2. 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

Parasympathetic Nerve :

1. Baroreceptors detect rise in blood
   pressure or chemoreceptors detect
   blood fall in blood CO2 conc. or rise in blood pH
2. 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