Contraction/Conduction Flashcards
resistance =
resistance =(mean art p - central venous p)/CO
blood flow =
blood flow = diff pressures/resistance
blood flow is proportional to
the driving force; pressure difference
relative refractory period
greater than normal stimulus needed to generate a propogated AP
effective action potential
propagated AP cannot be elicited
absolute refractory period
AP cannot be elicited NO matter what
fast APs occur in
contracting regions (atrial and ventricular mm) fast conduction (his/purkinje) LEFT side
slow APs occur in
pacemaking (SA node)
slow conduction (AV node)
RIGHT side
AP is fast or slow depending on
speed of initial depolarization
Fast; Phase 0
rapid depol, Na inward
Fast; Phase 1
initial repolarization;
inactivation of Na
open outward K (Ito)
activ
Fast; Phase 2
Plateau
slowly act inward Ca currents
(atrial and ventricular contraction)
Fast; Phase 3
repolarization
inactivation of Ca currents
act of several K out currents (Ikr, Iks)
Fast; Phase 4
resting mem potiential due to
inward K channels (Ik1)
Slow; Phase 0
slow depol
slowly activating Ca channels
Slow; Phase 1
absent
Slow; Phase 2
absent
Slow; Phase 3
repolarization
Ca channel deactivation
act of outward K channels
Slow; Phase 4
slowly depolarizing resting potential
pacemaking
due to slowly depol phase 4
rate of depol sets time it takes to reach threshold and thus firing rate
spontaneous depolarization
imbalance between Outward; ACh act K channels (Ik,ACh, Igirk) - hyperpolarize the cell Inward; nonsel cation channel HCN (If) - depolarize the cell
In>out = depolarization
PNS - acetylcholine & phase 4
ACh + muscarinic ACh receptors increases Igirk K+ currents reduces rate of depolarization (phase 4) - hyperpolarizes reduces heart rate (negative chronotropic effect)
SNS - epinephrine/NE & phase 4
beta 1 adrenergic receptors increases If and ICa (inward currents increase rate of phase 4 depol increases heart rate (postive chronotropic effect)
rate of SA nodal pacing can also be changed by changing diastolic resting pot/threshold;
changing the diastolic resting potential/threshold
PNS - diastolic pot more Neg -> increases threshold, reduces firing rate
SNS - diastolic pot more Pos ->
overdrive suppression
pacemaker w fastest rate of phase 4 depol and shortest AP controls heart rate
intrinsic rates (beats/min):
SA node 100
AV 40-60
His/P 30-40
slowest AP is in the
AV node
provides delay bet atrial and ventricular AP
important for pumping - allows for more efficient filling of ventricles before contraction
Autonomic NS can alter conduction velocity here too
positive dromotopic effect
increase conduction velocity of AV node
SNS
negative dromotopic effect
decrease conduction velocity of AV node
PNS
