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Electrical activity of the heart
N/A
56
Physiology
Graduate
01/04/2012

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Cards

Term
Membrane potential is dependent on what?
Definition
Ionic diffusion
Term
Membrane potential is created primarily due to what ion?
Definition
K+
Term
Contracting and conducting cardiac myocytes respond to what type of action potential?
Definition
Fast-response
Term
Pacemaker cells in the SA and AV node respond to what type of action potential?
Definition
Slow-response
Term
What is the resting membrane potential in fast-response cardiac myocytes?
Definition
-90mV/-80mV
Term
What is the resting membrane potential in slow-response pacemaker cells?
Definition
-60mV
Term
What occurs during phase 0 of an action potential in ventricular cardiac myocytes?
Definition
Rapid depolarization
Term

What occurs during phase 1 of an action potential in ventricular cardiac myocytes?

Definition
Early partial repolarization
Term

What occurs during phase 2 of an action potential in ventricular cardiac myocytes?

Definition
Plateau phase
Term

What occurs during phase 3 of an action potential in ventricular cardiac myocytes?

Definition
Final repolarization
Term

What occurs during phase 4 of an action potential in ventricular cardiac myocytes?

Definition
Resting potential
Term
What causes rapid depolarization during phase 0 in cardiac myocytes?
Definition
Rapid Na+ influx through voltage gated channels
Term
What causes early partial repolarization during phase 1 in cardiac myocytes?
Definition
Efflux of K+ and the transient outward K+ current
Term
What causes the plateau phase during phase 2 in cardiac myocytes?
Definition
Increased Ca++ conductance
Term
What causes final repolarization during phase 3 in cardiac myocytes?
Definition
Efflux of K+ exceeds the influx of Ca++
Term
The resting potential during phase 4 in cardiac myocytes is determined chiefly by what?
Definition
K+ conductance
Term
Which refractory period is absolute?
Definition
Effective refractory period
Term
When does the effective refractory period occur?
Definition
During phases 0, 1, and part of 3
Term
What causes the effective refractory period?
Definition
Inactivation of voltage gated Na+ channels
Term
What is required to elicit an action potential during a relative refractory period?
Definition
Suprathreshold stimuli
Term
What causes a relative refractory period
Definition
All Na+ have not been completely reactivated
Term
Effective refractory periods protect the heart by preventing what?
Definition
Tetany
Term
Voltage gated channels participating in phase 0 depolarization of non-pacemaker cardiac APs describes what?
Definition
Fast Na+ channels
Term
What maintains resting membrane potential in phase 4, and permits K+ outflow at highly negative potential in cardiac cells?
Definition
Inward rectifier (Iir or Ikr) K+ channels
Term
What contributes to phase 1 by transiently permiting K+ outflow at positive membrane potential?
Definition
Transient outward (Ito) K+ channels
Term
What contributes to phase 3 repolarization of cardiac action potentials and permits K+ outflow?
Definition
Delayed rectifier (Ikr) K+ channels
Term
What effect do acetycholine and adenosine have on cardiac myocyte action potentials?
Definition
G-protein coupled receptors hyperpolarizes membrane during phase 4 and shortens phase 2
Term
What voltage-gated channels provide a slow inward, long lasting current, and are responsible for phase 2 non-pacemaker cardiac APs?
Definition
L-type calcium channels
Term
The unstable resting potentials of autorhythmic pacemaker cells are called what?
Definition
Pacemaker potentials
Term
What do pacemaker cells use for the upstroke of the action potential during phase 0
Definition
Ca++ influx
Term
When does the ionic current upstroke occur in pacemaker potentials?
Definition
Phase 0
Term

When does the ionic current repolarization occur in pacemaker potentials?

Definition
Phase 3
Term

When does the ionic current slow (spontaneous) depolarization occur in pacemaker potentials?

Definition
Phase 4
Term
Slow depolarization during phase 4 of paemaker potentials occurs due to the opening of what?
Definition
Funny current (If) Na+ channels
Term
When do funny current (If) Na+ channels open and close?
Definition
During hyperpolarization (-60mV) and depolarization (-20mV) 
Term
As the pacemaker potential becomes more positive, what channels begin to open?
Definition
L-type Ca++ channels
Term
What opens in the latter part of phase 4, casuing a small increase in Ca++
Definition
T-type Ca++
Term
Inactivation of voltage gated Ca++ channels and opening of voltage gated delayed K+ channels occurs during what phase of a pacemaker potential?
Definition
Phase 3
Term
What term refers to the relative refractory period in pacemaker cells extending beyond phase 3?
Definition
Post-repolarization refractoriness
Term
What are the effects of post-repolarization refractoriness in pacemaker cells?
Definition
Recovery of full excitability is much slower than in fast-response AP, leads to conduction blocks
Term
Slow Na+ channels (If) acting in pacemaker potentials are also known as what?
Definition
Funny pacemaker current
Term
Delayed rectifier (Ikr) potassium channels are active during what phase of pacemaker potential?
Definition
Phase 3 of reporlarization of cardiac action potentials
Term
Are ATP-sensitive (Ik, ATP)  open or closed during a pacemaker potential when ATP decreases?
Definition
Open
Term
What effect do protein coupled, Ach-activaed potassium channels (Ik, Ach) have on pacemaker potentials?
Definition
Slows pacemaker potential via hyperpolarization during phase 4
Term
How do L-type (ICa-L) calcium channels modulate pacemaker potentials?
Definition
Creates slow, inward, long-lasting current important in vascular smooth muscle contraction
Term

What phase are L-type (ICa-L) calcium channels active during non-pacemaker cardiac action potentials?

Definition
Phase 2
Term
What phase are L-type (ICa-L) calcium channels active during pacemaker potentials of SA and AV nodal cells?
Definition
Phase 4 and 0
Term
T-type (ICa-T) calcium channels are associated with what type of current in pacemaker potentials?
Definition
Transient current
Term
In what phase areT-type (ICa-T) calcium channels active during pacemaker potentials in SA and AV nodal cells?
Definition
Phase 4
Term
What is the order of conduction of electrical impulses?
Definition
SA -> AV -> Ventricles
Term
A normal heart rate falls between what range?
Definition
60-100 b/min
Term
The vagus nerve has projections on what part of the heart?
Definition
SA and AV node
Term
Sympathetic nerve fibers inenrvate what parts of the heart?
Definition
Primarily cardiac muscle, very little pacemaker cells
Term
Sympathetic (NE) neurons have what effect on the heart?
Definition
Stimulation, positive chronotropic, dromotropic, and ionotropic effects
Term
Parasympathetic (Ach) neurons have what effect on the heart contraction?
Definition
Inhibition via negative chronotropic, dromotropic, and ionotropic effects
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