6.1.3 Control of heart rate ( 3.6 Organisms respond ti changes in their internal and external environments)

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

Where is the Sinoatrial node (SAN) , Atrioventricular node ( AVN) , Bundle of His and the Purkyne tissue

Answer 2

SAN is at the top left ,
AVN is lower down to the left
Bundle of His is in the middle
Purkyne tissue is at the bottom

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 a 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 branched 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 ( Fall in blood pressure OR rise in blood CO2 concentration/ fall in blood pH)

Answer 5

1) Baroreceptors detect fall in blood pressure and / or chemoreceptors detect blood rise in 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 muscles contracts more frequently
6) so heart rate increases

Question 6

Describe the roles of chemoreceptors , pressure receptors, the autonomic nervous system and effectors in controlling heart rate ( Rise in blood pressure OR fall in blood CO2 concentration/ rise in blood pH)

Answer 6

1) Baroreceptors detect rise in blood pressure and or chemoreceptors detect fall in blood CO2 conc of 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 muscles contracts less frequently
6) So heart rate decreases