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32 Cards in this Set

  • Front
  • Back
What are the two categories of the cardiac cells?
*Miocardial Cells (working or mechanical cells)
*Pacemaker Cells (electrical cells)
What are myocardial cells?
They are working or mechanical cells that contain contractile filaments.
What are pacemaker cells?
Specialized cells of the electrical conduction system responsible for the spontaneous generation and conduction of electrical impulses
Major electrolytes that affect cardiac function
*Sodium (Na+)
*Potassium (K+)
What determines the cell's electrical charge?
The differences of the electrolyte concentration.
Normal cell charge
*Excess of + ions on outside
*Excess of - ions on inside
Membrane potential
Difference in electrical charge across the membrane.
Action potential
Five-phase cycle that reflects the differences in the concentrations of the ions across the cell membrane at any given time.
Two types of action potentials
Fast Response Action Potentials
*Occur in cells of atria, ventricles, and Purkinje fibers.
*Occurs b/c of the presence of may Na+ channels that allow a rapid influx of Na+ when these channels are open and prevent influx when they are closed
Slow Resonse Action Potentials
*In SA and AV nodes
*Have slow Ca++ and slow Na+ channels
*Can sometimes occur anywhere in the heart, usually secondary to ischemia, injury or an electrolyte imbalance.
Polarization (resting membrane potential)
*Resting state, no electrical activity
*Intracellular ions include K+ and some anions (neg. charged ions)
*When the cardiac cell is stimulated.
*Inside of cell becomes more positive b/c of the entry of Na+ ions into the cell through Na+ membrane channels.
*Proceeds from endocardium to epicardium
P Wave
Atrial depolarization
QRS Complex
Ventricular depolarization
*Pulseless Electrical Activity
*Occurs when there is electrical activity on the monitor but no palpable pulse
*The diffusion of Na+ into the cell stops
*K+ is allowed to diffuse out of the cell, leaving the anions inside the cell.
*Occurs b/c of outward diffusion of K+
*Proceeds from epicardium to endocardium
ST Segment
Early ventricular repolarization
T Wave
Ventricular Repolarization
Phases 1,2,3 of cardiac action potential
Electrical Systole
Phase 4 of the cardiac action potential
Electrical Diastole
Phase 0 of the cardiac action potential
*Rapid depolarization phase / upstroke / spike / overshoot
*Begins when the cell receives an impulse.
Phase 1 - Early Repolarization

Cardiac Action Potential Cycle
*Fast Na+ channels partially close, slowing the flow of Na+ into the cell.
*K+ moves out of the cell rapidly
*Positive electrical charges within the cell decrease, producing a small negative deflection in the action potential.
Phase 2 - Repolarization (Plateau Phase)

*Plateau = a raised flat area

Cardiac Action Potential Cycle
*Occurs b/c of slow, inward movement of Ca++ and continued movement of K+ outward.
*Allows cardiac muscle to sustain an increased period of contraction.
*ST segment
*Is a part of the absolute refractory period.
Phase 3 - Rapid Repolarization

Cardiac Action Potential Cycle
*The cell rapidly completes repolariztion as K+ flows quickly out of the cell and the slow channels close, stopping the influx of Ca++ and Na+.
*The rapid efflux of K+ from the cell causes it to become progressively more electrically negative.
*T Wave
Phase 4 - Resting Membrane Potential

Cardiac Action Potential Cycle
*Return to the resting state
*Excess of Na+ inside the cell and excess of K+ outside the cell.
*Cell will remain in this state until the cell membrane is reactivated by another stimulus.
Refractory Period
The extent to which a cell is able to respond to a stimulus. Longer than contraction.
Absolute Refractory Period

*aka Effective Refractory Period
*Corresponds with the onset of the QRS complex to the peak of the T Wave and includes phases 0, 1, 2, and part of phase 3 of the cardiac action potential.
*Myocardial cell will not respond to further stimulation
Relative Refractory Period

*aka Vulnerable Period
*Corresponds w/ the downsloap of the T Wave
*Some cardiac cells have repolarized to their threshold potential and can be stimulated to respond (depolarized) to a stronger than normal stimulus.
Supernormal Period
*A weaker than normal stimulus can cause depolarization of cardiac cells.
*Extends from the terminal portion of phase 3 of the action potential to the beginning of phase 4
*End of T-Wave
*It is possible for cardiac dysrrhythmias to develop during this period.
Four primary properties of cardiac cells
Automacity, excitability, conductivity, and contractility
Ability of cadiac pacemaker cells to spontaneously initiate an electrical impulse w/o being stimulated from another source.