Lecture #3 Flashcards
Purpose of Goldman-Hodgkin-Katz equation?
Calculate membrane potential
What is the Goldman-Hodgkin-Katz equation at body temperature?
E= (61.5) log10 [(Px(Xout) + …..)/(Px(Xin))]
What is the Nernst equation for K
(61.5) log 10 (Kout/Kin)
Changes of ion conductances will cause
Changed in membrane potential
Difference between an atrial and ventricular action potential?
Ventricular action potential lasts longer
In the typical ventricular action potential drawing (pg 4), what does phase 4 represent?
Resting Potential
Electrical activity in resting potential?
Outward K generated I-K2P current
Inward K current generates IK1 current
What does Phase 0 represent?
What electrical activity is going on?
Rapid Opening of voltage-gated sodium channels
I-Na current
What does Phase 1 represent?
What electrical activity is going on?
Closing of the voltage-gated Na channels
Voltage gated outward K curent
What does Phase 2 represent?
What electrical activity is going on?
The Plateau
Reduced outward K (I-K1) coupled with inward Ca current (I-Ca(L))
What does Phase 3 represent?
What electrical activity is going on?
Repolarization
Closure of L-type Ca channels
Increase in outward K (I-ks and I-Kr)
Inward rectifier channels close……
Example of an inward rectifier
when the cell depolarizes
I-K1
Difference between L-type and T-type Ca channels
T-types are in SA and AV nodes
L-types are in heart muscle cells for plateau
Name the five types of potassium currents
Inward Rectifier Slow delayed outward rectifier Rapid delayed outward rectifier leak channels transient outward
Difference between effective refractory period and relative refractory period?
Effective – 2nd depolarization has no effect
Relative – Some channels are reset, more difficult to restim
Two sources of calcium in plateau stage
Ca enters through L type channels
Entering Ca triggers release from SR
How do catecholamines influence Ca levels?
Cate. act on beta-1 adren. receptors
Inc. cAMP and PKA
P of L-type Ca Channels
Increased inotropic state
How to block catecholamines on the heart?
beta-blockers
What might cause failure of the SA node? What would happen?
Occlusion of the sinus node artery
Pacemaker fxn taken over by AV node
What is an escape rhythm?
When another pacemaker takes over for a defective SA
What is an ectopic focus?
The area where spontaneous depolarization of a non-SA portion of the heart can occur
Why are ectopic foci a concern?
They can trigger serious arrhythmias
SA node has ______ stable resting potential.
No
What is the pacemaker potential?
A slow depolarization of the cell caused by “funny current”
Funny current mainly moves what ion?
Na
What channels trigger SA action potential?
Initially Voltage gated T-type Ca channels
Later, L-type Ca channels open
Describe the SA action potential cycle
P4 – Sodium Leak Current generates depolarizing prepotential
P0 – At -40mV, Ca channels open, triggering AP
P3 – Ca channels close, Na perm. decreases, K’s open
Effect of PS stim on pacemaker?
Vagus decreases HR via Muscarinic ACh receptors
Increased K permeability in SA nodes
Takes longer for prepotential to reach firing threshold
Effect of Symp. on pacemaker?
Stim HR via nore. on beta-1 adrenergic receptors
K channels close more rapidly
Less time for prepotential to reach firing threshold
Route of electrical charge in pacemaker system
SA depolarizes, Signal spreads through atrial myocardium AV depolarizes AV-bundle (Common Bundle of His) L and R Bundle Branches Purkinje Fibers Ventricular Muscle Fibers
Three parts of AV Node
Junctional, Nodal, Transitional
Unique part of AV in the conduction pathway?
Why we care?
Delays conduction of the electrical impulses
Allows time for the atria to contract and relax before ventricular systole.
Other name for fibrous portion of the heart?
Annulus fibrosis
Cause of Wolf-Parkinson-White and Lown-Ganong-Levine syndromes?
Abnormal, accessory pathways that bypass the AV
List Five things that influence conduction velocity.
Sympathetic Stim (+) Vagal Stim (-) Hypoxia/Ischemia (-) Adrenergic/Cholinergic (+/-) Hyperkalemia/Cocaine (-)
EKGs require ____ leads
12
For ED patients with chest discomfort, an EKG should be performed within _______.
10 minutes
Significance of P wave?
Dep. of atria
Significance of P-R Interval
Time for impulse to pass through AV node
Significance of QRS complex
Depolarization of ventricles
Significance of T Wave?
Ventricular Repolarization
Significance of S-T segment?
When elevated, indicates potential myocardial infarction
Significance of Q-T Interval?
Prolonged in long-QT syndrome
What is U wave?
Sometimes seen after T
Sign of hypokalemia, digoxin, quinidine
What is J point?
Jxn of QRS and ST segment
Where is the atrial repolarization in the EKG?
Hidden in the QRS
