Cardiac Muscle Flashcards
What are the three ways cardiac muscle APs differ from skeletal muscle APs?
they’re self generating
they conduct directly from cell to cell
they have a long duration
What are the three most important ions for cardiac APs?
sodium, calcium, potassium
On what side of the membrane is sodium concentration higher? calcium? potassium?
sodium and calcium are higher in the interstitial fluid (so they want to move into the cell)
Potassium is high in th eintracellular fluid, so it wants to move out
What structures in the membrane are responsible for the resting membrane potential and rapid changes?
ion channels
What are the three possible states of ion channels?
open, closed, inactivated
What is the resting membrane potential for cardiac cells? Closes to what ion equilibrium?
-90 mV - which is potassium’s equilibirum
What are the two types of myocardial cells?
myocardial contractile cells
myocardial autorhythmic cells = pacemaker cells
Contractile cell APs are similar to neurons exept for what important difference?
much longer AP due to extended Ca2+ entry
How can pacemakers spontaneously generate APs?
their membrane potential is inherently unstable
Which cells produce the “slow response” and which produce the “fast response”
pacemaker cells = slow response
contractile cells = fast response
How many phases are there in a contractile cell AP?
5, but they’re numbered 0-4
For contractile cells, what is the first step in firing an AP?
the Na channels open and the K+ channels close. THis means K+ can’t leave the cell and Na+ rushes in. This causes a rapid depolarization.
For contractile cells, what happens at the peak - the overshoot?
the Na+ channels close and FAST K+ channels open. K+ is now wanting to enter the cell based on the electrochemical gradient - this is what makes the initial repolarization happen briefly.
It doesn’t last long though - the K+ channels close
After the fast K+ channels close, what opens?
the slow inward Ca2+ channels open. Ca 2+ enters the cell very slowly, halting the repolarization and causing the characteristic plateau
What causes the repolarization after the plateau?
the Ca2+ channels close and the delayed rectifier slow K+ channels open, allowing K+ to rush out of the cell causing the rapid repolarization
What slows the rapid repolarization such that the resting membrane is reached and maintained?
the slow K+ channels close and the inward rectifier channels open when you reach the K+ resting membrane potential
What current characterizes the pacemaker cells
the funny current
what are the phases of the apcemaker cell AP/
three phases: 0, 3, and 4 to coincide with the contractile
What makes the funny current funny?
both Na and K are going in and out
What causes the potential to gradually rise?
a gradual influx of Na
When the potential reaches a threshold, what happens?
you have a transient opening of the Ca2+ channels and you get an influx of Ca2+ to further depolarize
How does the influx of Ca2+ essentially sustain itself?
It triggers long-lasting Ca2+ channels to open
What causes the depolarization to stop and then result in repolarization?
opening of the K+ channels so K leaves the cell
So what ion primarily mediates phase 0 in contractile cells/ in pacemaker cells?
Na in contractile
Ca in pacemaker
