6.4 Cardiac action potentials Flashcards
What regulates cardiac action potentials?
action potentials in the Intrinsic Conduction System (NOT the nervous system)
What are funny channels, what do they do?
Unique to pacemaker cells. Na+ channels
-60mV to -50mV
open at -60mV
How to cardiac pacemaker cells depolarize?
- 50mV to -40 mV: T-type Ca2+ channels open, Ca2+ in
- 40 mV to 0: L-typle Ca2+ channels open, cell quickly depolarizes to 0
How do cardiac pacemaker cells repolarize?
Ca2+ channels close, K+ channels open, back to -60mV, cycle restarts
What is the resting potential for cardiomyocytes?
-90mV
Describe cardiomyocyte depolarization
-90mV to +20mV INSTANTLY
Na+ channels open, Na+ IN
What is the plateau phase?
+20mV to 0mV
Na+ inactivate
Ca2+ open, Ca2+ in
Creates a long refractory period to allow muscle time to respond to the AP, contract fully before next signal
Describe cardiomyocite repolarization
0 to -90 mV
Ca2+ channels close
K+ open, K+ IN
How do action potentials spread through heart muscle?
Action potentials will spread through cardiac muscle gap junctions and lead to contraction of cardiac muscle
Within the heart muscle cell, what happens when an action potential is received?
myocardium,T-tubules depolarize
Ca2+ enters via extracellular Ca2+
Sarcoplasmic Reticulum releases Ca2+ into the sarcoplasm **”Calcium induced calcium release”
Ca2+ binds troponin, releases tropomyosin
CROSSBRIDGES form requiring ATP
Why is a long refractory period important?
Protects against dysrhythmias
In a supra ventricular dysthymia, what pacemaker cells are involved? What part of the heart?
SA, AV nodes
atria
In a ventricular dysthymia, what pacemaker cells are involved? What part of the heart?
Bundle to His
Purkinje fibers
Ventricle
What is a heart block?
conduction between the atria and ventricles is not functioning properly (atria and ventricles beat independently)
