Electrical Properties of the Heart I Flashcards
What occurs in phase zero?
Rapid depolarization
What occurs in phase one?
Rapid but incomplete repolarization (not SA/AV)
What occurs in phase two?
Plateau
What occurs in phase three?
Slow, delayed repolarization
What occurs in phase four?
Slow, diastolic depolarization (not atrial/ventricular myocardium)
What effect on action potential does hypokalemia have?
Prolongs action potential
What channels are active in phase 0?
Sodium current
What channels are active in phase 1?
Ikto- transient inward current potassium
What channels are active in phase 2?
Ica-t: transient
Ica-l: long
What channels are active in phase 3?
Ikur: terminates phase 2
Ikr: sustains depolarization
Iks: sustains depolarization
What channels are active in phase 4?
NCX
Voltage dependent IK1
What is a relative refractory period?
Time when the cell is still repolarizing but is still able to send an action potential with enough stimulus
What is effectively refractory period defined as?
2x the threshold current
What tract runs anterior?
Bachman’s bundle
What tract runs posterior?
Thorel’s tract
What tract runs middle?
Wenckebach’s tract
What agents close gap junctions or cause uncoupling?
Acidosis/ischemia
ATP depletion/ischemia
Increased intracellular calcium/injury
Where are connexons found in normal heart cells?
End to end
Where are connexons found in fibrosis?
Side to side
What PSNS nerve innervates the heart?
Vagus nerve
What does the right vagus nerve innervate?
SA node
What does the left vagus nerve innervate?
AV node
What is If funny current?
Pacemaker channel present in SA and AV nodes; determinant of automaticity
What regulates the current of If funny channels?
cAMP increased levels increases current
What are the effects of acetylcholine?
Decreased cAMP and If (diastolic depolarization)
Increased IkACH (hyperpolarization)
Decreased Ica-L SR Ca2+ release decreased NCX
What affect does an increase in IkACH channels cause?
Decreased pacemaker activity
