Excitation of the Heart Flashcards
The atria conduct ___ seconds faster than the ventricles
0.16s (1/6 of a second)
The excitatory conductive system is located in the superior posterolateral wall of the ______
right atrium
Fibers of the excitatory conductive system have almost no what?
contractile muscle filaments
Fibers of the excitatory conductive system connect directly with what type of muscle fibers?
atrial
The AV node is located on the posterior wall of the right ____ behind the ____ valve
atrium; tricuspid
The AV node causes ___ conduction and delay, which contribute to both physiology and function
slow
AV node causes rapid transmission in which system?
Ventricular purkinje system
The velocity of the AV node action potential is ____x of the ventricular fibers and ____x that of AV nodal fibers
6x; 150x
Action potentials are not able to travel which direction from the ventricles to the atria?
backwards
Action potentials are not able to travel backwards from the ventricles to the atria in order to prevent re-entry of what?
cardiac impulses
Re-entry of cardiac impulses from the atria to the ventricles can cause serious what?
arrhythmias
Impulse spreads at a moderate velocity through the ____ and is delayed more than 0.1s in the ___ nodal region
atria; AV
Impulses then spread very rapidly through the ____ fibers to the ___ surfaces. They spread less rapidly through the ventricular muscle to the ___ surfaces
purkinje
endocardial
epicardial
The purkinje system has ___ conduction and ____ contraction
rapid; synchronous
Which node is considered the normal pacemaker of the heart?
SA node
Which fibers discharge at an intrinsic rhythmical rate rate of 40-60x per minute (when not stimulated by an outside source)?
AV nodal fibers
Which fibers discharge at a rate somewhere between 15-40x per minute?
purkinje fibers
Which abnormal pacemaker will cause fainting after 4-5 seconds due to a sudden AV block?
Stokes-Adam syndrome
Which abnormal pacemaker causes an abnormal sequence of contraction of the different parts of the heart causing significant heart pump debility?
Ectopic pacemaker
The effect of Acetylcholine on the heart ____ the rate of rhythm in the sinus node and ____ excitability of the AC junctional fibers
decreases; decreases
Decreasing the excitability of the AV junctional fibers between the atrial musculature and the AV node will cause what?
slowing transmission of the cardiac impulse in the ventricles
Acetylcholine increases the permeability of what?
fiber membranes to K+ ions
Acetylcholine allows for rapid leakage of what?
K+ ions out of conductive fibers
Acetylcholine increases the ___ inside the fiber
negativity
Hyperpolarization is caused by
mechanisms of vagal effects (acetylcholine)
The tissue is ___ excitable in mechanisms of vagal effects (acetylcholine)
less
Ventricular Escape is when a strong vagal stimulation can stop rhythmical excitation by 2 things, which are what?
- Blocking the sinus node
2. Blocking the transmission of the cardiac impulse from the atria into the ventricles via AV-node
When the ventricles stop beating for 5-20 seconds and the purkinje fibers develop a rhythm of its own, causing ventricular contraction of 15-40bpm, what is this called?
Ventricular Escape
Sympathetic stimulation increases the rate of _____ discharge, the rate of ____, the level of _____ in all portions of the heart and the force of contraction of all cardiac musculature, both in ____ and ____
sinus nodal
conduction
excitability
atrial and ventricular
What are the mechanisms of sympathetic effects (5)?
- Norepinephrine (NE)
- NE stimulates B-1 andrenergic receptors
- Increases permeability of fiber membrane to sodium and calcium ions
- More positive membrane potential
- Tissue is more excitable
Norepinephrine stimulates what kind of receptors in the sympathetic system?
B-1 andrenergic receptors
Norepinephrine increases the permeability of fiber membrane to what 2 ions?
sodium and calcium
NE causes a more ____ membrane potential
positive
NE causes the tissue to be more ____
excitable
Where are normal rhythmical impulses generated?
SA node
A decrease in gap junctions causes what delay?
AV delay
An AV delay allows for the atria to empty their blood into the ventricles before what begins?
ventricular contraction
What allows for rapid conduction for full/synchronous contraction of the ventricles?
purkinje fibers
Parasympathetic activity releases what neurotransmitter?
Acetylcholine
Parasympathetic activity decreases the rate of what node?
SA node
Parasympathetic activity decreases the excitability of the AV junctional fibers between what 2 structures?
Atria and AV node
Sympathetic activity releases what neurotransmitter?
Norepinphrine
Sympathetic activity increases the rate of what node?
SA node
Sympathetic activity increases the contractile strength of the cardiac muscle through increased permeability of what ion?
calcium
