Lecture 5 Flashcards
Resting Heart Rate (Healthy Adult)?
70 bpm
Resting Heart Rate (Athlete)?
50 bpm
Resting Heart Rate (Newborn)?
135 bpm
Heart Rate Range?
20-250 bpm
ECG?
Measure when it contracts and relaxes and it has 12 leads
Factors affecting current flow?
1) Number of Cell-Cell Gap Junctions
2) Cell Diameter
3) Cell Alignment
Gap Junctions are made out of?
Connexons
Phase 0?
“Depolarization Phase”
-Activation of “fast” voltage-gated Na and Ca channels
(Inward Na flux and Ca flux)
Phase 1?
“Early Depolarization Phase”
-Activation of a “transient outward” voltage-gated K channels
(outward K flux) Inaction of Na channels
Phase 2?
“Plateau Phase” (because not repolarizing or depolarizing)
-Activation of voltage-gated Ca channels, Activation of “delayed rectifier” K channels (Inward Ca flux and outward K flux counteract each other)
Phase 3?
“Final Depolarization Phase”
-Inactivation of voltage-gated Ca current, Activation of delayed rectifier K channels, And inward rectifier K channels
(outward K flux)
Phase 4?
“Diastolic “Resting” Potential”
-Activated inward rectifier K channels
(outward K flux)
Different ion channels?
Na+, Ca2+, and K+
Depolarizing?
Inward Na+ and Ca2+ currents
Depolarizing/Hyper?
Outward K+ currents
Effective Refractory Period?
(ERP) Cell cannot fire another action potential
Relative Refractory Period?
(RRP) Cell can fire another action potential, but amplitude is reduced
ERP and RRP are caused by?
Inactivation state of voltage-gated Na and/or Ca channels
Automaticity?
Initiates Heart Beat
Rhythmicity?
Regular Pacemaking Activity
Dominant Pacemaker?
SA Node (with SA Node dysfunction, AV Node can become dominant pacemaker)
Resting Heart Rate is Reduced by?
Basal Parasympathetic Tone
Exercise reduces?
Parasympathetic tone increase Sympathetic tone
Duration of the Cardiac AP is significantly longer than the?
Neuronal AP
Cardiac AP being longer results in?
An extended refractory period that provides sufficient time for Heart chambers to fill with blood before depolarizing AP wave comes along
Pacemaker cells?
-Slower rising phase in Phase 0
-No early repolarization Phase 1
-No plateau phase Phase 2
-Presence of a slowly depolarizing “pacemaker” potential during Phase 4
-Phase 4 (“resting potential”) is more depolarized in pacemaker cells
Pacemaker cells?
-Slower rising phase in Phase 0
-No early repolarization Phase 1
-No plateau phase Phase 2
-Presence of a slowly depolarizing “pacemaker” potential during Phase 4
-Phase 4 (“resting potential”) is more depolarized in pacemaker cells
“Funny” Channel is responsible for?
Automaticity (all pacemaker cells express the “funny” channel)
(“Slow” Pacemaker AP)
Phase 0?
-No Na+ inward
-Calcium current
-Voltage-dependent Ca channel (slower because Ca2+ slower than Na+)
(“Slow” Pacemaker AP)
Phase 3?
-Potassium current
-Voltage-dependent K channel
-Ca+ closed
(“Slow” Pacemaker AP)
Phase 4?
-Involves Na+ channel
-“Funny” pacemaker current
-Cyclic-nucleotide gated Na channel
-Necessary for automaticity (because activated by hyperpolarization, increased Na+ slow depolarization of Phase 4)
SA Node Cell?
Membrane potential for triggering all-or-nothing AP
Altering automaticity and firing frequency (HR)?
1) Change slope of Phase 4 (increased time of depolarization)
2) Hyperpolarization during Phase 4 (increased time to depolarize)
3) A change in threshold for firing
Parasympathetic?
Rest and Digest
Sympathetic?
Fight or Flight
Heart is innervated by?
-Both parasympathetic and sympathetic nerves (mainly myocardial regions)
Innervation of nodal regions are?
Predominantly, but not exclusively, parasympathetic
