Electrophysiology of the Heart Flashcards
Na+ gradients
concentration - more outside the cell
electrical - more outside the cell
K+ gradients
concentration - more inside the cell
electrical - more outside the cell
Ca++ gradients
concentration - more outside the cell
electrical - more outside the cell
Cl- gradients
concentration - more outside the cell
electrical - more inside the cell
Protein- gradients
concentration - more inside the cell
electrical - more inside teh cell
Na+ permeability at rest
not permeable
Na/K ATPase is pumping it out of the cell
K+ permeability at rest
permable
Ca++ permeability at rest
not very permeable
concentration maintained by active sequestration into SR
Phase 0 permabilities
increased permeability to sodium
Phase 1 permabilities
decreased permeability to sodium
Phase 2 permeabilities
increased permeability to calcium
decreased permeability to K+
Phase 3 permeabilities
increased permeability to K+
decreased permeability to Ca++
When does Fast Na+/Ca++ channel open
Phase 0
When does slow Na+/Ca++ channel open
Phase 2
Effective refractory period
absolute refractory period, begins at upstroke of phase 0 and ends when Na+ channels are reset to resting potion in phase 3
Why can the heart not undergo tetany
because of the effective refractory period
Relative refractory period
begins where ERP ends. Ends when normal AP can be generated
Phase 0 of SA nodal pacemaker AP
upstroke/depolarization
Ca++ enters cell
Phase 3 of SA nodal pacemaker AP
repolarization
K+ exits cell
Phase 4 of SA nodal pacemaker of AP
slow depolarization/pre potential
Na+ enters cell via funny current
Example of positive Chronotroph
norepinephrine, epinephrine, isoproterenol
What does positive chronotroph do
increases permeability of nodal cells to N+ and Ca++
increases HR
What does postiive chronotroph do to slope
increased slope of phase 4
Example of negative chronotroph
acetylcholine
What does negative chronotroph do
increased permeability of nodal cells to K+, lowers resting potential
decreases HR
What does negative chronotroph do to slope
lowers slope of phase 4
What are ectopic foci
superexcitiable cells
What is the function of ectopic foci as fail safe mechanism
it helps if you have a blockage, the highest rate will pace the heart
Sequence of depolarization of the heart
SA node –> atrial muscle cells —> AV node —> septum –> apex —> free walls –> LV base
function of SA node
normal pacemaker for heart
function of AV node
delays impulse, secondary pacemaker
function of His bundle
normally only communication point between atria and ventricles
Function of purkinje fivers
very rapid transmission of signal, synchronous contraction of ventricles, tertiary pacemaker, only penetrate to subendocardium
average vector for atrial depolarization and duration
gap junctions/direct contact with neighboring atrial muscle cells. spread is instantaneous
average vector for ventricular depolarization and duration
purkinje fibers, quick at first but then spreads via mycoyte connections which are slower
how does hyperkalemia increase chance of fatal dysrthymia
hyperkalemia slows HR, blocks AV conduction and dilation of heart, cell membrane is partially depolarized which reduces intensity of AP and makes heart progressively weaker
