control of the heart Rate

Question 1

what does it mean by myogenic?

Answer 1

the stimulus for the cardiac muscle to contract at rest comes from the muscle itself

Question 2

describe the control of heart rate at rest

Answer 2

nervous impulse is produced from SAN and spreads across the atria causing the cardiac muscle to contract, contracting the atria and forcing blood through to the ventricles. The nervous impulse arrives at the AVN but doesn’t pass directly to the ventricles due to sections of non–conductive tissue. there is a delay at the AVN to allow the atria to finish contracting before the ventricles start to. the nervous impulse travels down the bundle of His in the purkinje tissue from the AVN to apex of ventricle. the bundle of His is non-conducting so they cannot pass out. the nervous impulse spreads up the ventricles in the purkinje fibres causing the cardiac muscle to contract from the bottom up and all blood from ventricles is expelled.

Question 3

where is the SAN located

Answer 3

wall of right atrium

Question 4

what is the role of the SAN in the control of cardiac cycle?

Answer 4

the SAN produces the nervous impulse that cause the cardiac muscle to contract

Question 5

how does exercise increase heart rate?

Answer 5

1. stimulus -increased CO2 levels due to more aerobic respiration. the CO2 dissolves in the blood plasma to make carbonic acid decreasing the PH
2. receptor- chemoreceptors in the walls of the aorta and carotid artery
3. electrical impulses sent to
4. co-ordinator - medulla oblangata
5. more electrical impulses sent in sympathetic nerve so fewer action potentials in parasympathetic nerves
   6.effector - SAN activity increased
6. response- HR increases

Question 6

how does decreased CO2 decrease heart rate?

Answer 6

1. decreased CO2 levels due to less aerobic respiration. CO2 dissolves in blood plasma making carbonic acid but less co2 made so ph drops less.
2. receptor- chemoreceptors in walls of aorta and carotid artery
3. more electrical impulses sent
4. co-ordinator - medulla oblongata
5. more electrical impulses in parasympathetic nerve so fewer in sympathetic nerves
6. effector- SAN activity decreased,
7. response- HR decreases

Question 7

describe how decreased blood pressure increases HR

Answer 7

stimulus- blood pressure drops

receptor- baroreceptors in walls of aorta and carotid artery

co-ordinator- medulla oblongata

more electrical impulses in sympathetic nerve so less in parasympathetic

effector - SAN activity increased

response- HR increases

Question 8

describe how increased blood pressure decreases heart rate

Answer 8

stimulus- blood pressure rises

receptor - baroreceptors in walls of aorta and carotid artery

electrical impulse sent

co-ordinator - medulla oblongata

more electrical impulses sent to parasympathetic nerves and less to sympathetic

effector - SAN activity decreased

response- hr decreases