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

see notes

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 → sends 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

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