2: Myocrdial Cells

Question 1

Order of electrical current through the heart

Answer 1

SA > AV > Bundle of HIS > Bundle branches > Purkinje fibers

Question 2

Ion fluctuations at rest

Answer 2

K+ channels open
ATP dependent Na/K pump
Outward movement of + charge

Question 3

Nerst Equasion

Answer 3

determine equilibrium potential for ions across selectively permeable membranes
= constant(K+in/K+out)

Question 4

Cardiac Resting membrane potential

Answer 4

= -90mV

Question 5

Neuron resting membrane potential

Answer 5

= -65mV

Question 6

Cardiac myocytes are impermeable or permeable to Na+

Answer 6

impermeable

Question 7

What causes changes in myocardial RMP

Answer 7

K+ levels

Question 8

Extracellular increases in K+ cause

Answer 8

depolarization of cardiac cells

Question 9

What effect does Na+ and Ca+ have on cardiac RMP

Answer 9

none

Question 10

Fast type

Phase 4

Answer 10

Resting membrane potential
K+ dependent
No Na or Ca conductance
Na/Ca exchange regulates Ca

Question 11

Fast type

Phase 0

Answer 11

Na+ open, flow in

Question 12

Fast type

Phase 1

Answer 12

Na+ rapidly close

K+ outward current

Question 13

Fast type

Phase 2

Answer 13

Slow opening of Ca+, flow in

K+ conductance decreased

Question 14

Fast type

Phase 3

Answer 14

Ca slowly close

K+ opens, leaves cell

Question 15

What is the action potential dependent on

Answer 15

Ca channel kinetics

Question 16

Absolute refractory period

Answer 16

Insure myocardial cells finish contraction

Allow sufficient diastolic filling time

Question 17

Relative refractory period

Answer 17

action potential will have less amplitude if activated