Lecture #3

Question 1

Purpose of Goldman-Hodgkin-Katz equation?

Answer 1

Calculate membrane potential

Question 2

What is the Goldman-Hodgkin-Katz equation at body temperature?

Answer 2

E= (61.5) log10 [(Px(Xout) + …..)/(Px(Xin))]

Question 3

What is the Nernst equation for K

Answer 3

(61.5) log 10 (Kout/Kin)

Question 4

Changes of ion conductances will cause

Answer 4

Changed in membrane potential

Question 5

Difference between an atrial and ventricular action potential?

Answer 5

Ventricular action potential lasts longer

Question 6

In the typical ventricular action potential drawing (pg 4), what does phase 4 represent?

Answer 6

Resting Potential

Question 7

Electrical activity in resting potential?

Answer 7

Outward K generated I-K2P current

Inward K current generates IK1 current

Question 8

What does Phase 0 represent?

What electrical activity is going on?

Answer 8

Rapid Opening of voltage-gated sodium channels

I-Na current

Question 9

What does Phase 1 represent?

What electrical activity is going on?

Answer 9

Closing of the voltage-gated Na channels

Voltage gated outward K curent

Question 10

What does Phase 2 represent?

What electrical activity is going on?

Answer 10

The Plateau

Reduced outward K (I-K1) coupled with inward Ca current (I-Ca(L))

Question 11

What does Phase 3 represent?

What electrical activity is going on?

Answer 11

Repolarization
Closure of L-type Ca channels
Increase in outward K (I-ks and I-Kr)

Question 12

Inward rectifier channels close……

Example of an inward rectifier

Answer 12

when the cell depolarizes

I-K1

Question 13

Difference between L-type and T-type Ca channels

Answer 13

T-types are in SA and AV nodes

L-types are in heart muscle cells for plateau

Question 14

Name the five types of potassium currents

Answer 14

Inward Rectifier
Slow delayed outward rectifier
Rapid delayed outward rectifier
leak channels
transient outward

Question 15

Difference between effective refractory period and relative refractory period?

Answer 15

Effective – 2nd depolarization has no effect

Relative – Some channels are reset, more difficult to restim

Question 16

Two sources of calcium in plateau stage

Answer 16

Ca enters through L type channels

Entering Ca triggers release from SR

Question 17

How do catecholamines influence Ca levels?

Answer 17

Cate. act on beta-1 adren. receptors
Inc. cAMP and PKA
P of L-type Ca Channels
Increased inotropic state

Question 18

How to block catecholamines on the heart?

Answer 18

beta-blockers

Question 19

What might cause failure of the SA node? What would happen?

Answer 19

Occlusion of the sinus node artery

Pacemaker fxn taken over by AV node

Question 20

What is an escape rhythm?

Answer 20

When another pacemaker takes over for a defective SA

Question 21

What is an ectopic focus?

Answer 21

The area where spontaneous depolarization of a non-SA portion of the heart can occur

Question 22

Why are ectopic foci a concern?

Answer 22

They can trigger serious arrhythmias

Question 23

SA node has ______ stable resting potential.

Answer 23

No

Question 24

What is the pacemaker potential?

Answer 24

A slow depolarization of the cell caused by “funny current”

Question 25

Funny current mainly moves what ion?

Answer 25

Na

Question 26

What channels trigger SA action potential?

Answer 26

Initially Voltage gated T-type Ca channels | Later, L-type Ca channels open

Question 27

Describe the SA action potential cycle

Answer 27

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

Question 28

Effect of PS stim on pacemaker?

Answer 28

Vagus decreases HR via Muscarinic ACh receptors Increased K permeability in SA nodes Takes longer for prepotential to reach firing threshold

Question 29

Effect of Symp. on pacemaker?

Answer 29

Stim HR via nore. on beta-1 adrenergic receptors K channels close more rapidly Less time for prepotential to reach firing threshold

Question 30

Route of electrical charge in pacemaker system

Answer 30

``` 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 ```

Question 31

Three parts of AV Node

Answer 31

Junctional, Nodal, Transitional

Question 32

Unique part of AV in the conduction pathway? | Why we care?

Answer 32

Delays conduction of the electrical impulses | Allows time for the atria to contract and relax before ventricular systole.

Question 33

Other name for fibrous portion of the heart?

Answer 33

Annulus fibrosis

Question 34

Cause of Wolf-Parkinson-White and Lown-Ganong-Levine syndromes?

Answer 34

Abnormal, accessory pathways that bypass the AV

Question 35

List Five things that influence conduction velocity.

Answer 35

``` Sympathetic Stim (+) Vagal Stim (-) Hypoxia/Ischemia (-) Adrenergic/Cholinergic (+/-) Hyperkalemia/Cocaine (-) ```

Question 36

EKGs require ____ leads

Answer 36

12

Question 37

For ED patients with chest discomfort, an EKG should be performed within _______.

Answer 37

10 minutes

Question 38

Significance of P wave?

Answer 38

Dep. of atria

Question 39

Significance of P-R Interval

Answer 39

Time for impulse to pass through AV node

Question 40

Significance of QRS complex

Answer 40

Depolarization of ventricles

Question 41

Significance of T Wave?

Answer 41

Ventricular Repolarization

Question 42

Significance of S-T segment?

Answer 42

When elevated, indicates potential myocardial infarction

Question 43

Significance of Q-T Interval?

Answer 43

Prolonged in long-QT syndrome

Question 44

What is U wave?

Answer 44

Sometimes seen after T | Sign of hypokalemia, digoxin, quinidine

Question 45

What is J point?

Answer 45

Jxn of QRS and ST segment

Question 46

Where is the atrial repolarization in the EKG?

Answer 46

Hidden in the QRS