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Physiology Ch.10
LECOM OMS1
46
Physiology
Professional
10/15/2011

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Term
The normal rhythmical impulse of the heart is generated in the ___.
Definition
sinus node aka sinoatrial node aka SA node
Term
The SA node is located ___.
Definition
superior posterolateral wall of the right atrium immediately below and slightly lateral to the opening of the superior vena cava
Term
Ventricular contraction in the normal heart has a delayed onset of ___ after the atrial contraction.
Definition
1/6 sec
Term
The ___ conduct the impulse from the sinus node to the atrioventricular (A-V) node.
Definition
internodal pathways
Term
The ___ conducts the impulse from the atria into the ventricles
Definition
A-V bundle
Term
The ___ conduct the cardiac impulse to all parts of the ventricles.
Definition
superior posterolateral wall of the right atrium immediately below and slightly lateral to the opening of the superior vena cava
Term
Does the sinus node tissue contract?
Definition
No, the fibers of this node have almost no contractile muscle filaments
Term
the resting membrane potential of the sinus nodal fiber between discharges has a negativity of about ___, in comparison with ___ for the ventricular muscle fiber.
Definition
negative 55 to negative 60 millivolts / negative 85 to negative 90 millivolts
Term
What is the natural permeability of sinus fibers?
Definition
leaky to sodium and calcium ions, these positive charges neutralize much of the intracellular negativity
Term
What types of channels are gound in cardiac muscle fiber?
Definition
1) fast sodium channels, (2) slow sodium-calcium channels, and (3) potassium channels.
Term
Opening of the ___ channels is responsible for the action potential observed in ventricular muscle
Definition
fast sodium
Term
Then the plateau of the ventricular action potential is caused primarily by ___ channels
Definition
slower opening of the slow sodium-calcium
Term
At this level of -55 millivolts or less, the fast sodium channels mainly have become ____.
Definition
inactivated, therefore, only the slow sodium-calcium channels can open to cause the action potential.
Term
When the potential reaches a threshold voltage of about ___, the sodium-calcium channels become activated, thus causing the action potential.
Definition
negative 40 millivolts
Term
Why does the leakiness to sodium and calcium ions not cause the sinus nodal fibers to remain depolarized all the time?
Definition
sodium-calciuminflux is inactivated about 100 to 150 milliseconds after the channel opens, then greatly increased numbers of potassium channels openallowing potassium efflux
Term
How is hyperpolarization caued in cardiac muscle?
Definition
potassium channels remain open for another few tenths of a second after negative resting level is reached, temporarily continuing movement of positive charges out of the cell, with resultant excess negativity inside the fiber
Term
The velocity of conduction in most atrial muscle is about ___, but can be as fast as ___, in several small bands of atrial fibers.
Definition
0.3 m/sec, 1 m/sec
Term
The anterior, middle, and posterior internodal pathways are bands that ___.
Definition
are located in the atrium, have faster contractility, and terminate in the AV node
Term
The anterior interatrial band passes ___.
Definition
through the anterior walls of the atria to the left atrium
Term
The A-V node is located ____.
Definition
in the posterior wall of the right atrium immediately behind the tricuspid valve
Term
The impulse, after traveling through the internodal pathways, reaches the A-V node about ___ after its origin in the sinus node.
Definition
0.03 second
Term
There is a delay of ___ in the A-V node itself before the impulse enters the penetrating portion of the A-V bundle, where it passes into the ventricles.
Definition
0.09 second
Term
A final delay of ___ occurs in the penetrating A-V bundle
Definition
0.04 second
Term
The total delay in the A-V nodal and A-V bundle system is about ___.
Definition
0.13 second
Term
There is a total delay of ___ before the excitatory signal finally reaches the contracting muscle of the ventricles.
Definition
0.16 second
Term
Purkinje fibers transmit action potentials at a velocity of ___.
Definition
1.5 to 4.0 m/sec
Term
Can action potentials to travel backward from the ventricles to the atria?
Definition
not under normal circumstances
Term
The distal portion of the A-V bundle passes downward in the ventricular septum and divides into ___ in the ___.
Definition
left and right bundle branches that lie beneath the endocardium on the two respective sides of the ventricular septum.
Term
The total elapsed time of transduction from the bundle branches in the ventricular septum to the terminations of the Purkinje fibers is ___.
Definition
0.03 second
Term
The velocity of transmission in the ventricular muscle fibers themselves is ____.
Definition
0.3 to 0.5 m/sec
Term
Transmission from the endocardial surface to the epicardial surface of the ventricle requires ___.
Definition
0.03 second
Term
The total time for transmission of the cardiac impulse from the initial bundle branches to the last of the ventricular muscle fibers in the normal heart is about ___.
Definition
0.06 second
Term
Impulse spreads at moderate velocity through the atria but is delayed ___ in the A-V nodal region before appearing in the ventricular septal A-V bundle.
Definition
0.1 second
Term
The A-V nodal fibers, when not stimulated from some outside source, discharge at an intrinsic rhythmical rate of ___, and the Purkinje fibers discharge at a rate between ___.
Definition
40 to 60 times per minute / 15 and 40 times per minute
Term
The pacemaker of the heart is the ___.
Definition
the sinus node because its rate of rhythmical discharge is faster than that of any other part of the heart
Term
A pacemaker elsewhere than the sinus node is called an ___.
Definition
ectopic pacemaker
Term
When A-V block occurs a new pacemaker usually develops in the Purkinje system of the ventricles and drives the ventricular muscle at a new rate of ___.
Definition
15 and 40 beats per minute
Term
What is Stokes-Adams syndrome?
Definition
An AV block of 5 to 20 seconds when the ventricles fail to pump blood- person faints after the first 4 to 5 seconds
Term
Stimulation of the parasympathetic nerves to the heart (the vagi) causes the hormone ___ to be released at the vagal endings.
Definition
acetylcholine
Term
What is the effect of parasympathetic innervation on the heart?
Definition
decreases the rate of rhythm of the sinus node, andt decreased excitability of the A-V junctional fibers between the atrial musculature and the A-V node
Term
What is ventricular stimulation?
Definition
Strong vagal stimualtion causes the ventricles stop beating for 5 to 20 seconds, but then some point in the Purkinje fibers, usually in the ventricular septal portion of the A-V bundle, develops a rhythm of its own and causes ventricular contraction at a rate of 15 to 40 beats per minute.
Term
What does acetylcholine do to potassium channels in the heart?
Definition
it increases the permeability of the fiber membranes to potassium ions, which allows rapid leakage of potassium out of the conductive fibers causing hyperpolarization
Term
In the sinus node, the state of hyperpolarization decreases the resting membrane potential of the sinus nodal fibers to a level of ___.
Definition
negative 65 to negative 75 millivolts
Term
Stimulation of the sympathetic nerves to the heart (the vagi) causes the hormone ___ to be released at the vagal endings.
Definition
increases the rate of sinus nodal discharge, rate of conduction, and level of excitability in all portions of the heart
Term
Stimulation of the sympathetic nerves releases the hormone ___ at the sympathetic nerve endings.
Definition
norepinephrine
Term
What does norepinephrine so to sodium-potassium channels?
Definition
increases the permeability of the fiber membrane to sodium and calcium ions accelerating self-excitation
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