Lecture 3: Neural Control Of The Heart

Question 1

What is the pathway of the signal in the heart?

Answer 1

SA node, through internal pathways, AV node, bundle of His, bundle branches, parking fibres, ventricle

Question 2

Where is the SA node?

Answer 2

Where major vessels enter the heart

Question 3

How many heart contractions does one AP lead to?

Answer 3

1

Question 4

What is the cardiac muscle RMP?

Answer 4

-90mV

Question 5

What is the cardiac pacemaker cell RMP?

Answer 5

-40mV

Question 6

What is the sequence of events in cardiac contraction?

Answer 6

• Fast Na channels open
• Fast Na channels close
• L-type Ca channels open
• K channels open
• RMP

Question 7

How does the AP of pacemaker cells work?

Answer 7

Never stable RMP, always drifting up. Slow creep back up to threshold.

Question 8

Are most cardiac cells capable of becoming pacemakers, why don’t they?

Answer 8

Yes. SA node dominates because it is the fastest.

Question 9

When are cells at risk of becoming ectopic pacemakers?

Answer 9

If they are injured and depolarised and close to threshold

Question 10

What is the parasympathetic neurotransmitter?

Answer 10

ACh

Question 11

What is the sympathetic neurotransmitter?

Answer 11

NAd

Question 12

What receptor responds to ACh?

Answer 12

Muscarinic

Question 13

What receptor responds to NAd?

Answer 13

Beta-1

Question 14

Where does ACh act and how does it act?

Answer 14

SA/AV nodes

Decrease HR

Question 15

Where does NAd act and how does it act?

Answer 15

SA/AV nodes and ventricle

Increase HR and contraction

Question 16

What happens if there is increased sympathetic stimulation to the heart?

Answer 16

Increased depolarising calcium current, reach threshold earlier, AP, faster heart rate

Question 17

What is the signalling pathway for NAd?

Answer 17

• G protein (Gas)
• GTP binds to alpha
• Alpha leaves beta&gamma
• Adenylyl cyclase generates cAMP
• cAMP stimulates calcium and ifunny channels
• More depolarisation
• Increase HR

Question 18

What happens if there is increased parasympathetic stimulation to the heart?

Answer 18

Increased hyper polarising current, slow depolarisation, takes longer to reach threshold, fewer APs, reduced HR

Question 19

What is the signalling pathway for ACh?

Answer 19

• G protein (Gai)
• GTP binds to alpha
• Beta&gamma bind to potassium channel
• Increase potassium flow
• Hyperpolarisation
• Reduce HR

Question 20

What is the refractory period and what is it like in cardiac muscle?

Answer 20

Unresponsive to stimulus.

Long refractory period in cardiac muscle, due to inactivation of l-type calcium channels, protects against early re-excitation

Question 21

What is the baroreceptor reflex?

Answer 21

Controls BP, high pressure receptors in aortic arch and carotid sinus, signals to brain about stretch, actions to regulate BP

Question 22

What is the bainbridge reflex?

Answer 22

Low range pressure receptors in atria, pulmonary artery and right ventricle - detect venous return and BV - when it increases it tells kidney to lose sodium and water to reduce BV