Cardiac Muscle--Nordgren Flashcards
These ions are present in great concentration outside cells
Na+
Ca2+
This ion is present in great concentration inside cells
K+
What is the RMP of cardiac contractile cells?
~-90 mV
Permeability of an ion is directly proportional to…
the number of open channels for that ion
What are the 2 types of myocardial cells?
contractile
pacemaker
What is the biggest difference between phase 0 of contractile and pacemaker cells?
contractile: Na+ is depolarizing ion
pacemaker: Ca2+ is depolarizing ion
What causes the slowing of AP through the AV node, allowing the atria and ventricles to contract independent of one another?
decreased number of gap junctions in the AV node
Phase 0 is what part of the cardiac cell potential diagram?
depolarization
Permeability of a substance is directly proportional to…
number of open channels
What is the approximate default rate of the SA node?
~100 bpm
Why is the SA node <100 bpm baseline?
parasympathetic tone
How does parasympathetic slowing of the heart muscle occur?
ACh –> mAChR
M2 muscarinic receptor
increased K+ flow
decreased Ca2+ flow
=> prolongs time to depolarization
Sympathetic activation of cardiac muscle
NE –> Beta-1 androgenic receptors
increase funny current activity (increased Na+ flow)
increased HR (chronotropic effect)
increased Ca2+ conductance –> increased contractility
What requires the largest amount of energy in the cardiac cycle?
isovolumic contraction
(overcoming afterload)
What is the most important controlable determinant of heart workload?
HR
decreased HR –> less CO
since venous pressure is 0, arterial pressure has to go down
Q = ΔP/R
