Chapter 1.b Concept Review: Action Potential - Pacemaker Cell Flashcards
how many phases is action potential of pacemaker cells divided into?
3; phases 0, 3, and 4
what distinguishes pacemaker cells from myocardial cells?
spontaneous phase 4 depolarization (upsloping phase 4)
which electrolyte slowly results in gradual rise of membrane potential towards its threshold potential?
slow influx of Na+
current responsible for phase 4 depolarization is AKA
pacemaker current or funny current (I(f))
once threshold potential is attained, which electrolyte causes depolarization of the cell during phase 0?
influx of Ca++
which electrolyte channel is opened, and which electrolyte channel is closed during repolarization, phase 3?
- efflux of K+
- closure of Ca++ channels
what happens when the membrane potential returns to its resting potential?
Na+ channels IMMEDIATELY open again
how is phase 4 directly affected?
sympathetic and parasympathetic tone
how does sympathetic stimulation affect phase 4?
steeper phase 4, and faster heart rate
how does norepinephrine affect the membrane’s permeability?
increases permeability to Na+
what decreases the slope of phase 4 and, consequently, the HR?
vagal tone
what increases the cell membrane’s permeability to K+ while decreasing its permeability to Na+?
ACh release by the vagus nerve
