Ventricular Muscle Flashcards
What is cardiac muscle contraction triggered by?
Action potential at the sarcolemma
Where does the electrical excitation occur?
Sinoatrial node
At rest, is the inside of the plasma membrane negative or positive with respect to the outside?
negative
What sets up the membrane potential?
Uneven distribution of ions
What ions are the main ions in the modulation of membrane potential in cardiac myocytes?
Ca2+, K+ and Na+ ions
What happens when channels open?
Ions flow down their concentration gradient
What happens at rest with K+?
K+ leaks out through Kir channels
Generating current iKir/iK1 (- 80mV)
What causes the depolarization in electrical activity?
Na+ influx
What causes the plateau in electrical activity?
Ca2+ influx
What causes the repolarization in electrical activity?
K+ influx
What is the refractory period?
No summation of contractions.
What does the refractory period permit?
Filling of the ventricles between contractions
Describe what happens in phase 0 of ventricular AP?
AP reaches adjacent myocyte
depolarization begins
overshoot generated
sodium channels open and inactivate rapidly
closure occurs as repolarization progresses
Describe what happens in phase 1 of ventricular AP?
Brief repolarization caused by Ito through K+ channels
Activated and inactivated quickly
Describe what happens in phase 2 of ventricular AP?
Plateau period with iCa through L-type Ca2+ channels
Reduced iKir
Describe what happens in phase 3 of ventricular AP?
K+ efflux increases through Kv channels
Describe what happens in phase 4 of ventricular AP?
Kir reopen to complete repolarization
Kv close when resting Vm is reached
Resting Vm re-established
Ca2+ pumped back to SR via Ca2+-ATPase
Remainder extruded by 3Na+/Ca2+ exchangers
ib reduces Vm (less negative)
What stimulates cardiac myocytes?
Adrenergic stimulation which increases iCa which increases contractility
What shortens the AP?
Sympathetic stimulation - repolarization occurs sooner
shorter duration = more APs per min
Define arrhythmias?
Abnormalities in electrical conductance which causes HR or cardiac rhythm disturbances
What shortens AP duration due to KATP opening?
Hypoxia
What can lengthen the plateau period?
Certain mutations to channel protein variants?
How are arrhythmias treated?
Block sodium channels
blocked sympathetic nerve activity
prolong refractory period
block calcium channels
