Cardiac electrophys

Question 1

In the myocardium, the resting membrane potential is determined by what?

Answer 1

Conductance of K+ and approaches the K+ equilibrium potential

Question 2

Ventricular myocardial cells have a table resting membrane potential of what?

Answer 2

-90 mV (K+ equilibrium potential)

Question 3

Describe Phase 0 in myocardium

Answer 3

1. Upstroke of the action potential. Transient increase in Na+ conductance.
2. Causes inward Na+ current - depolarization

Question 4

Describe Phase 1 in the myocardium.

Answer 4

1. Brief period of initial depolarization - Outward current due to:
   
   1. K+ move out
   2. Decreased Na+ conductance

Question 5

Describe phase 2 of the myocardium.

Answer 5

1. Plateau phase
   
   1. Transient increase in Ca+ conductance - Inward Ca+ current
   2. increased K+ conductance (outward)
   3. Inward and outward currents are similar, so plateau

Question 6

Describe phase 3 of the myocardium

Answer 6

1. Repolarization (phase 3)
   
   1. Ca+ conductance decreases
   2. Large outward K+ current - hyperpolarizes the cell back to RMP

Question 7

Describe phase 4 of myocardial potential.

Answer 7

Resting membrane potential

Inward and outward currents are equal - membrane potential reaches K+ equilibrium potential

Question 8

Describe phase 0 of the pacemaker cells.

Answer 8

Slow upstroke in the action potential.

Inward Ca2+ current that drives the membrane toward the Ca2+ equilibrium potential

Question 9

Describe phase 3 of the pacemaker electrical potential.

Answer 9

Repolarization (phase 3)

Increase in K+ conductance. Outward K+ current

Question 10

Describe phase 4 of the pacemaker electrical potential.

Answer 10

Slow depolarization (phase 4)

Increase in Na+ conductance - Inward Na+ current (funny current)

Question 11

What phases are NOT present in pacemaker cells?

Answer 11

Phase 1 and phase 2