Lecture 24- Cardiovascular Electrophysiology Flashcards
Why are cardiomyocytes excitable?
There is an electrochemical gradient maintained across the cell membrane
What ions are most important for myocardial contraction?
Na, K, and Ca
What is the equation for conductance?
1/resistance
What is conductance?
How easily a current flows
What type of cells can depolarize spontaneously and found in nodes and the bundle of His?
Specialized Conduction Cells
What cells are found in the cardiac muscle, and are excitable if given a stimulus?
Working cardiocytes
What is normal automaticity?
The ability to spontaneously generate an action potential
What is the dominant pacemaker of the adult heart?
SA node
What is inherent rate?
Rate of firing independent of autonomic influence
What does sympathetic tone do to sinus rate
Increases
What does vagal tone do to sinus rate?
Decreases
What is the only electrical connection between the atria and the ventricles?
The AV node
What part of the heart is a “functional syncytium” and why
The myocardium- because it acts as if it is one cell due to the intercalated discs and gap junctions allowing rapid ion diffusion
What is moved using the sodium potassium pump?
3 Na+ out
2 K+ in
What is the Donnan effect
Large anions (proteins) are enclosed by a membrane
What ion is the selective permeability of the cardiomyocytes permeable to when resting?
K leaks out
What are voltage-gated K ion channels responsible for?
Repolarization
What is the inward rectifier K ion channel responsible for
Maintaining resting membrane potential
What are the voltage-gated sodium channels responsible for?
Letting Na+ in for depolarization
When do voltage-gated Ca channels open
When the inside of the cell becomes positive
What are the types of Ca voltage-gated ion channels?
L- type (slow)
T-type
What is different between cardiomyocyte and neuron action potentials?
Cardiac APs last longer (plateau)
What does the cardiomyocyte action potential plateau cause?
No physiological tetanus
Is the plateau longer in the SA node or the Purkinje fibers?
The Purkinje fibers
What is another name for Bundle of His
AV bundle
Depolarization of working cells is driven by
Sodium channels
Depolarization of nodal cells is driven by
Calcium channels
Arrhythmias should be treated in nodal cells or working cells?
Working cells
What phase do fast Na channels open
0
What phase do slow Ca channels open
2
What phase do K channels open?
3- repolarization (delayed rectifier)
4- inward rectifier
What is overdrive suppression
The nodal cell depolarizing at the fastest rate sets the pace for the other nodal cells
What kind of Na channels is used in spontaneous depolarization in addition to Ca and K?
If (funny)
How are sympathetic neurons distributed through the myocardium?
Diffusely
How are parasympathetic neurons distributed through the myocardium
Regionally localized
What are the sympathetic vs parasympathetic neurotransmitters?
S: Epi and Norepi
P: Ach
