Cardiac Action Potentials (Mine) Flashcards
In what order does the action potential in the heart spread?
SA node
AV node
Bundle of His
R/L Bundle Branch (left is more subdivided)
Purkinje Fibers
Which areas can have pacemaker properties under the right conditions?
What keeps all these areas from trying to be pacemakers all at the same time?
SA node (generates AP most frequently)
AV node (delay at AV node)
Purkinje fibers (least frequent)
Overdrive Suppresion maintains order of pacemakers
What is the conduction velocity of the following?
- Atria:
- AV node:
- His-Purkinje:
- Ventricle:
- 1m/s
- 0.01-0.05m/s
- 2-4m/s
- 1m/s
What is the rule of thumb when it comes to velocity in terms of diameter?
What is the order of velocity from most to least
cells/fibers with larger diameters are faster
purkinje>atrial/ventricular muscle>AV node
Which atrium fires first, left or right?
Which layer fires first, endocardium or epicardium?
Which ventricle epicardium fires first, right ventricle or left ventricle?
Right atrium fires first
Endocardium fires first
Right ventricle epicardium fires first
know how to draw and label the cardiac action potential diagrams with labels for the ventricle, atrium, and SA node on slide 8
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Phase 0
what’s open and what’s closed?
Voltage gated Na channels open
IK1 close
depolarization stage
Phase 1
What’s open and what’s closed?
Inactivation gates of Voltage Gated Na channels close
Ito opens
this causes the dip between 1-2
Phase 2
What’s open and what’s closed?
Ca opens
Ito closes (which kicks of phase 2)
Iks open
plateau
Phase 3
What is open and what is closed?
Ca closed
Ikr and Iks reach max openess
rapid repol due to Ik1 opening
repolarization
Which K channel opens at phase 3’s peak?
IKr, IKs (rapid/slow)
Phase 4
What’s open/closed?
leaky K channels and other maintanance channels to keep membrane at rmp.
How does Na enter the cardiac myocytes?
Via voltage-gated Na channels
this is important for refractory periods
Inward Ca movement from L type Ca channels are somewhat responsible for which phase?
Phase 2
Transient outward K movement (Ito) are partially responsible for which phase?
Phase 1
What channels and ions are responsible for transitioning between phase 2 and 3?
voltage gated K channels and outward flow of K
Which K ions exhibit inward flow and close during phase 0, stopping some of the K flow and maintaining phase 2?
IK1 (K1) ions
these channels open again to help with phase 3.
The inward Ca flow and outward K flow with the inward K flow lead to which phase?
Phase 2
K leak channels, which are typically open all the time, would increase outward flow during which phase?
Phase 2
In Phase 4, the SA node and AV node resting membrane potential do what?
What about the SA node makes it the pacemaker?
Which ion channels open upon complete repolarization of the membrane?
gradually depolarize until reaching threshold and then fire, but slower than other regions
intrinsic spontaneous depolarization
If/INaf (voltage gated Na channels)
What is happening with the flow of ions in Phase 0?
opening of voltage gated Ca channels rather than voltage gated Na channels and closure of voltage-gated K channels (rectifiers)
What parts of the heart are primary sources of rhythmicity?
SA and AV node
What is happening with the ion flow during phase 3?
Reversal of phase 0, closure of voltage gated CA channels and opening of voltage gated K channels (both rectifiers and traditional)
Overdrive suppresion dictates that stimulation of the AV node by the SA node will trigger what?
Will trigger the AV node to generate an action potential prior to when it would do so on its own
this also prevents bundle branches and PK fibers from firing spontaneously as their rate of phase 4 is even slower
Why are refractory periods longer in cardiac cells?
to help prevent arrythmias
What is an absolute refractory period?
What is a relative refractory period?
What is a supranormal period?
ARP: No AP can be generated
RRP: AP can be generated, requires greater stimulus or has abnormal conduction
SNP: Cell is more excitable than normal and easier to generate AP, have abnormal conduction
If a cell is in relative refractory or supranormal period, and it is stimulated, what will happen?
The conduction of the AP will be weaker
Define Chronotropic
changes in heart rate
+ faster
- slower
Define Dromotropic
effect speed of conduction (conduction velocity), slope of phase 0
Define inotropic
define lusitropic
Will learn about these later
effect strength of muscular contraction
effect rate of muscular relaxation
Parsymphathetic innervation of the heart by the vagus nerve does what?
travels to SA and AV node, but insignificantly affects ventricular myocytes
uses Ach as a NTM
Muscarinic (M2/M3 receptor)
What are the parasympathetic negative chronotopic effects?
- slower opening of funny Na channels during phase 4
- hyperpolarization of SA node by increasing outward K current via specialized K channels (K-ach channels)
What are the parasympathetic negative dromotropic effects?
- reduced inward Ca current
- hyperpolarization of SA node by increasing outward K current via special K channels (K-ach channels)
What are the sympathetic effects on the heart?
To SA, AV, and ventricular myocytes, and atrial cells
Ues NE as NTM
Receptor is B1-adrenergic
What are the sympathetic positive chronotropic effects?
- More rapid opening of “funny” Na channels during phase 4
- Hyperpolarization of SA node by decreasing outward K current via special K channels (K-ach)
What are the sympathetic positive dromotropic effects?
- increased inward Ca current
- hyperpolarization of SA node by increasing outward K current via special K channels (K-ach)
As far as heart rate goes, what is the affect of sympathetic stimulation?
What is the affect of parasympathetic stimnulation?
“Hypopolarize”, increased inward Na
“Hyperpolarize”, decrease inward Na
