Lecture 3: Neural Control Of The Heart Flashcards
What is the pathway of the signal in the heart?
SA node, through internal pathways, AV node, bundle of His, bundle branches, parking fibres, ventricle
Where is the SA node?
Where major vessels enter the heart
How many heart contractions does one AP lead to?
1
What is the cardiac muscle RMP?
-90mV
What is the cardiac pacemaker cell RMP?
-40mV
What is the sequence of events in cardiac contraction?
- Fast Na channels open
- Fast Na channels close
- L-type Ca channels open
- K channels open
- RMP
How does the AP of pacemaker cells work?
Never stable RMP, always drifting up. Slow creep back up to threshold.
Are most cardiac cells capable of becoming pacemakers, why don’t they?
Yes. SA node dominates because it is the fastest.
When are cells at risk of becoming ectopic pacemakers?
If they are injured and depolarised and close to threshold
What is the parasympathetic neurotransmitter?
ACh
What is the sympathetic neurotransmitter?
NAd
What receptor responds to ACh?
Muscarinic
What receptor responds to NAd?
Beta-1
Where does ACh act and how does it act?
SA/AV nodes
Decrease HR
Where does NAd act and how does it act?
SA/AV nodes and ventricle
Increase HR and contraction
What happens if there is increased sympathetic stimulation to the heart?
Increased depolarising calcium current, reach threshold earlier, AP, faster heart rate
What is the signalling pathway for NAd?
- 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
What happens if there is increased parasympathetic stimulation to the heart?
Increased hyper polarising current, slow depolarisation, takes longer to reach threshold, fewer APs, reduced HR
What is the signalling pathway for ACh?
- G protein (Gai)
- GTP binds to alpha
- Beta&gamma bind to potassium channel
- Increase potassium flow
- Hyperpolarisation
- Reduce HR
What is the refractory period and what is it like in cardiac muscle?
Unresponsive to stimulus.
Long refractory period in cardiac muscle, due to inactivation of l-type calcium channels, protects against early re-excitation
What is the baroreceptor reflex?
Controls BP, high pressure receptors in aortic arch and carotid sinus, signals to brain about stretch, actions to regulate BP
What is the bainbridge reflex?
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
