Heart 1

Question 1

Working myocardium

Answer 1

Atrial and ventricular muscle

Question 2

Specialized conduction system

Answer 2

SA node, internodal pathways, AV node, bundle of His, bundle branches, Purkinje fibers

Question 3

P wave

Answer 3

Atrial activation

Question 4

QRS complex

Answer 4

Ventricular activation

Question 5

T wave

Answer 5

Ventricular recovery

Question 6

Difference between Nernst and Goldman-Katz equations

Answer 6

Nernst gives the theoretical equilibrium potential with only taking into account the ions in question; Goldman-Katz gives the actual resting membrane potential considering ALL ions in the solution

Question 7

What pharmaceutical inhibits the Na-K pump?

Answer 7

Digitalis - has been in use in medicine for the last 200 years, but the mechanism of action has only been known for the last 30

Question 8

Na-Ca exchange

Answer 8

Exchanges 3 sodium ions in for one calcium ion out to produce an electrogenic net inward current

Question 9

How is the sodium-calcium exchange indirectly affected?

Answer 9

Since sodium is also being used to exchange potassium, the concentrations of sodium will flux within the cell and indirectly affect calcium exchange

Question 10

Anomalous rectification

Answer 10

A decrease in potassium permeability that occurs when either the electrical or chemical driving force on potassium is increased

Question 11

What are the two reasons for the deviation between the predicted Ek by Nernst and the actual Vm?

Answer 11

Small amount of sodium influx and a decrease in potassium permeability when the concentration is within normal limits and lower

Question 12

Which is better for the heart: hyperkalemia or hypokalemia?

Answer 12

Hypokalemia, due to anomalous rectification

Question 13

What happens with K current during the action potential plateau?

Answer 13

K permeability decreases, which then delays repolarization

Question 14

Normal physiological concentration of potassium

Answer 14

3-5 meq/L

Question 15

Describe the consequences of hyperkalemia

Answer 15

It increases membrane potassium permeability, which decreases K+ concentration gradient across the membrane. This creates a more positive membrane potential

Question 16

Describe the consequences of hypokalemia

Answer 16

Decreases membrane potassium permeability due to inward rectification. It then increases the potassium gradient across the membrane, but there is no measurable effect due to the anomalous rectification.

Question 17

Waveform in the SA node

Answer 17

Continuous rise and fall; no true “resting” phase

Question 18

Phase 0

Answer 18

Upstroke of AP due to influx of sodium

Question 19

Phase 1

Answer 19

Peak and fall due to closing of sodium channels and opening of the potassium channels

Question 20

Phase 2

Answer 20

Plateau phase: continuation of efflux of potassium (inward rectification), net influx of calcium

Question 21

Phase 3

Answer 21

Fall of plateau due to closing of calcium channels. Potassium channels remain open

Question 22

Phase 4

Answer 22

Resting phase; only potassium channels remain open. Sodium channels are available, but non-active

Question 23

Effect of TTX on phase 0

Answer 23

Fast sodium channels are blocked so fast upstroke is now the responsibility of slow Ca2+ channels

Question 24

Effect of TTX on phases 2-4

Answer 24

None

Question 25

Fast response action potentials activate what?

Answer 25

Both fast sodium AND slow calcium channels during initial upstroke

Question 26

What happens with local damage to heart tissue?

Answer 26

Fast responses can become slow responses from infarct, so the damaged region can slow dramatically and cause arrhythmias due to reentry of excitation

Question 27

Where do slow responses happen in the heart?

Answer 27

The SA node and AV node

Question 28

What phases do slow response waves lack?

Answer 28

1 and 2

Question 29

Membrane potential for slow response tissue and its threshold

Answer 29

-40 to -60 with threshold of -40 mV

Question 30

In what tissues do fast responses happen?

Answer 30

Atrial, His-Purkinje, ventricular

Question 31

Membrane potential and threshold for fast response cells

Answer 31

-90 to -80 with a threshold of -65 mV