Flashcards in Session 7 Deck (63)
What is tension in myocardial cells proportional to?
The concentration of calcium in.
What changes occur to the calcium concentration to cause systole and diastole?
Systole - calcium concentration increases
Diastole - calcium concentration decreases
What is the equilibrium potential?
The hypothetical membrane potential that would develop if it was the only ion that could cross the membrane.
Myocardial cells have which voltage gated channels.
Sodium, potassium and calcium.
These are to present in the pacemaker cells!
What is the cell membrane mostly permeable to in diastole?
What is the membrane voltage during diastole?
Extra point - Why?
Because it is only permeable to potassium, it is close to the equilibrium potential for potassium.
What happens when the initial depolarisation reaches the threshold?
Fast voltage gated sodium channels open.
The membrane potential goes closer to the sodium equilibrium potential and depolarises further.
Once the fast voltage gated sodium channels are open, the close fast too. What stops the membrane from repolarising quickly?
Calcium voltage gated channels.
What does calcium entering the cell stimulate?
Intracellular stores to release calcium, causes contraction.
How long do the calcium channels stay open for?
What channel opens while the calcium channels are open to cause depolarisation to occur faster?
Potassium voltage gated channels.
Do pacemaker cells have fast sodium channels?
What causes the upstroke (once threshold is reached) in pacemaker cells?
Slow calcium channels.
Why is the action potential short in pacemaker cells?
Because calcium channels close quickly.
Once the action potential has finishes, what causes it to depolarise slowly?
The membrane potential is not stable so the ion permeability alters.
What is the significance of pacemaker cells having no fast sodium channels?
They are not sensitive to the membrane potential.
What does the interval between beats depend on?
How fast the pacemaker cells depolarise.
What speeds up pacemaker depolarisation?
What slows down the pacemaker potential?
How does noradrenaline speed up the heart rate?
Makes the pacemaker potential steeper.
How do acetylcholine slow the heart rate?
Makes the pacemaker potential shallower.
What can CVS drugs treat?
Arrhythmias, heart failure, angina and hypertension.
What can CVS drugs alter?
Rate and rhythm of the heart, the force of contraction, blood flow and blood volume.
What can cause disorders of rhythms?
Ectopic pacemaker activity.
What is ectopic pacemaker activity?
Where a damaged area (can be from MI) becomes active.
What can allow after depolarisations?
Anything that prolongs the action potential.
What are the 4 classes of anti arrhythmia drugs?
Drugs that block voltage sensitive sodium channels.
Antagonists of beta adrenoreceptors.
Drugs that block potassium channels.
Drugs that block calcium channels.
Give an example of a drug that blocks the voltage sensitive sodium channels.
Local anaesthetics such as lidocaine.
Give an example of an antagonist of beta adrenoreceptors.
-called beta blockers.