Cardiac Flashcards
Pacemaker cells are located in what 2 nodes?
SA and AV
These depolarize only when electrical impulses (APs) initiated by the SA or AV node are transmitted to them.
Non-pacemaker Cells
What is a cellular mechanism that allows pacemaker cells to depolarize spontaneously?
There is no true resting membrane potential
What is the primary transport mechanism responsible for the generation of the action potentials of pacemaker cells?
Passive diffusion of ions
Nodal or pacemaker cells exhibit an unstable RMP during ____ which begins at maximal value of about -65mv and slowly becomes less negative towards 0 mv until threshold is reached.
Phase 4
In phase 4 as the maximum diastolic potential is reached three changes (2 early and 1 late in the phase) occurring causing the membrane to slowly depolarize toward threshold, what are they?
- An influx of Na+ through “funny” cation channels
- A decrease in membrane permeability of K+ (not as much K+ can exit the cell)
- Late in phase 4, transient “T” type Ca++ channels open
In phase 0, when the membrane potential reaches threshold (~-40 mv), ____ open allowing Ca++ to enter the cell and generate an AP.
Long lasting “L” type Ca++ channels open
In phase 3, when does repolarization occur?
when the membrane permeability to K+ increase. Consequently, K+ leave the cell and the membrane potential moves toward the equilibrium potential for K+.
If a drug increase the K+ leak rate of a pacemaker cell, what effect does it have on the maximal diastolic potential?
It is more negative (Hyperpolarization)
If a drug increases the Ca++ permeability of the L-type calcium channels in a pacemaker cell, what effect does it have on the amplitude of phase 0 of the action potential?
It increases
Is the action potential of non-pacemaker cells similar to the action potential of pacemaker cells?
No; phase 4 is more of a true resting membrane potential
Why are the shapes of the non-pacemaker cell and the pacemaker cell action potentials so different?
There are different/other ion channels involved
The cardiac cell RMP in a non-pacemaker cell is established principally by:
- The difference in the concentrations of individual ions across the cell membrane established mainly by the _____.
- The difference in the cell membrane permeability to _____.
- Na+/K+ ATPase exchange pump
2. sodium and potassium ions
In the resting state, the cell membrane is more than 100 times more permeable to ___ than to ____.
Potassium than to sodium
During phase 1 of the action potential, a … is activated when the inside of the cell becomes positive.
Transient Potassium Efflux Channel (Ito)
The opening of this channels returns the membrane potential from about +20 mV to a value near 0 mV. This channel conducts potassium OUT of the cell.
Ito
During the plateau (phase 2), another …. becomes active, permitting potassium to be conducted out of the cell.
Potassium Channel (Ik)
This channel is responsible for Repolarization (Phase 3) and establishing the RMP.
Ik
Fast sodium influx channel has a voltage threshold of about … and when activated, sodium ions diffuse along their concentration and electrical gradients.
-70 mV (voltage-gated)
Fast sodium influx channel is responsible for phase ___ and is activated and inactivated very rapidly (time dependent).
phase 0
The fast sodium channel is blocked by the drug, …
tetrodotoxin
Calcium influx channel has an activation threshold voltage of about … and when activated, the membrane permeability to calcium ions increases, allowing these ions to diffuse along their electrochemical gradient.
-40 mV
Calcium influx channel is primarily responsible for phase ___.
phase 2
The calcium channel is blocked by voltage-gated calcium channel blockers like
Verapamil
What is the permeability status of K+ in early phase 2?
First a K+ spike, then decreasing K+ (Ito)
What is the permeability status of Ca+ in early phase 2?
increasing Ca++
What is the permeability status of Ca++ in late phase 2?
decreasing Ca++
What is the permeability status of K+ in phase 3?
increasing K+ (Ik)
What channels open during phase 0 of the action potential, but due to their slow influx they don’t contribute towards the amplitude (positive voltage) of phase 0.
Calcium channels
