3 Basic Electrophysiology Flashcards
Why is a cell’s resting membrane potential negative?
Normally -60 to -90 mV mainly because of the contribution of the resting potential of K
What is an equillibrium potential?
When the ion no longer diffuses (no net flux) in/out of the membrane because the electric potential balances the ion concentration gradient
**Electric force= Chemical forces
What is depolarization?
Na/Ca ion influx into the cell, making the membrane potential more positive
What is repolarization?
K ion flux out of the cell making the membrane potential return to more negative values
Why does an action potential travel in one direction?
Inactivation of Na channels
What is the effective refractory period?
Period that extends a little beyond absolute refractory period where depolarization can occur but not enough to generate an AP
**TIME and NEG voltage necessary for inactivated Na channels to open again

What is the functinal reason the AV node delays AP transmission?
Allows time for atria to empty their blood into the ventricles
What portion of the EKG corresponds to the length of the AP?
QT interval= AP duration
What are the ion concentrations in mM that contribute to the resting membrane potential?
- K
- contributes the most!
- 4 mM outside
- 140 mM inside
- Na
- 140 mM outside
- 10 mM inside
- Ca
- 2.4 mM outside
- ~50 nM inside

How do you calculate the equilibrium potential?
The Nernst equation (ion valence z in equilibrium at the nernst equilibrium)
RT/zF= 26 for monovalent
What is the Na/K ATPase?
Active transport for the uptake of 2K and extrusion of 3Na against their concentration gradients
What is the Na-Ca exchanger?
Forward mode; extrudes 1Ca out of the cell/3Na enter
Reverse mode; 1Ca enters/3Na exit
What is the Ca-ATPase?
Ca pump that extrudes Ca out of the cell
What is the SERCA?
Sarco/endoplasmic reticulum Ca-ATPase
**returns Ca ions back into the lumen of the SR
Contrast the AP of myocytes and nodal cells

What are the phases/channels of a myocyte AP?
- phase 0= Na channel
*depolarization - phase 1= Kto channel
- phase 2= Ca-L, NaCa, Kr, Ks channels
*delicate balance, easily perturbed
*plateau phase - phase 3= Kr, Ks, K1, KAch/ATP channels
*repolarization - phase 4= K1, KAch/ATP channels
*resting phase
What can cause long QT syndrome?
Block or dysfunction of K channels can delay repolarization of the cardiac AP
**prolonged QT can lead to “early after depolarization” (break of threshold leading to ectopic beats/torsades des pointes)

What is torsades des pointes?
“Twisting of the points”
Polymorphic ventricular tachycardia that can lead to sudden cardiac death
What is the physiological result of persistant Na channels?
Mutant Na channels incompletely close the inactivation gate resulting in an increased level of persistent current
**associated with hyperkalemic periodic paralysis, long QT syndrome, and inherited epilepsy
Describe the cardiac pacemaker depolarization
“Funny” Na current is carried by HCN (hyperpolarization-activated cyclic nucleotide-gated)
**HCN is voltage gated and regulated/activated by cAMP
What creates the refractory period of nodal cells?
Due to the inactivation of Ca channels (take longer to recover)