2: Myocrdial Cells Flashcards
Order of electrical current through the heart
SA > AV > Bundle of HIS > Bundle branches > Purkinje fibers
Ion fluctuations at rest
K+ channels open
ATP dependent Na/K pump
Outward movement of + charge
Nerst Equasion
determine equilibrium potential for ions across selectively permeable membranes
= constant(K+in/K+out)
Cardiac Resting membrane potential
= -90mV
Neuron resting membrane potential
= -65mV
Cardiac myocytes are impermeable or permeable to Na+
impermeable
What causes changes in myocardial RMP
K+ levels
Extracellular increases in K+ cause
depolarization of cardiac cells
What effect does Na+ and Ca+ have on cardiac RMP
none
Fast type
Phase 4
Resting membrane potential
K+ dependent
No Na or Ca conductance
Na/Ca exchange regulates Ca
Fast type
Phase 0
Na+ open, flow in
Fast type
Phase 1
Na+ rapidly close
K+ outward current
Fast type
Phase 2
Slow opening of Ca+, flow in
K+ conductance decreased
Fast type
Phase 3
Ca slowly close
K+ opens, leaves cell
What is the action potential dependent on
Ca channel kinetics
Absolute refractory period
Insure myocardial cells finish contraction
Allow sufficient diastolic filling time
Relative refractory period
action potential will have less amplitude if activated
