Cardiac Conduction System Flashcards

S-A node
Terms Definitions
Cardiac Conduction System
Page 100
apex
ventricular contraction proceeds in a wave that begins at the ______ and spreads towards the base
contractile myocytes
heart cells that actually contract, become shorter, and push blood through the chambers of the heart and artery. these cells compose the vast majority of the heart itself
initiate, distribute
myofibrils of the cardiac muscle function to _____ and ________ impulses throughout the myocardium
Electrocardiogram (EKG)
a recording of the electrical changes that occur in the myocardium during a cardiac cycle; used to assess the heart's ability to conduct impulses
interdigitating folds, mechanical junctions, gap junctions
three characteristics of intercalated discs
does not
impulse _____ _____ pass directly into ventricular syncytium because the fibrous skeleton of the heart separates it from the atrial syncytium
atrioventricular node
located in the inferior portion of the interatrial septum just beneath the epicardium; functions to slow the spread of impulse to the ventricles; cells of it depolarize more slowly; the only normal conduction pathway between the atrial and ventricular syncytium
Sinoatrial node (SA node)
also called the pacemaker; in cardiac muscle tissue in right atrium near the opening of superior vena cava; contracts on their own and initiate impulses, it is also rhythmic
right atrium
S-A node is located in the _____ _____ near the opening of the superior vena cava; just beneath the epicardium; fibers are continuous with those of the atrial syncytium; impulses generated by the S-A node ultimately reach all parts of the heart
Functional syncytium
a mass of merging cells that act as a unit
purkinje fiber (subendocardial fiber)
fibers at the bottom of the heart which branch extensively and help deliver the action potentials to all the contractile myocytes of the ventricles (and cause the ventricles to contract)
T-wave
ventricular muscle fibers re-polarize slowly
automaticity
when cardiac muscle tissue contracts on its own, without neural or hormonal stimulation; aka autorhythmicity
defibrillator
a machine that delivers an electric shock to the heart, and hopefully stops fibrillation
purkinje fibers
these spread from the interventricular septum into papillary muscles and continue downward to the apex of the heart, curve around the tips of the ventricles and pass upward over the lateral walls of these chambers; along the way they give off many small branches which become continuous with cardiac muscle fibers; radiate from the apex to the base of heart
Atrioventricular Node (AV)
The atrioventricular node or junctional node is located in the inferior wall of the right atrium close to the tricuspid valve.
P-wave
occurs when SA node triggers a cardiac impulse, atrial fibers depolarize
gap junction
places in the intercalated discs where the cytoplasm of one cardiac myocyte, actually connects to, and is continuous with the cytoplasm of an adjacent cardiac myocyte; allows for electrical connections b/w adjacent cells
atrial syncytium
cardiac impulse travels from S-A node into _______ ______ (mass of cardiac muscle fibers along atrial wall) via junctional fibers (internodal fibers) resulting in almost simultaneous contraction of the left and right atria
intercalated discs
the ends of every cardiac myocyte that connects the cells to one another, and allows action potentials to move so rapidly (allowing for coordinated beats)
A-V bundle
this enters the upper part of the interventricular septum and divides into left and right bundle branches that lie just between the endocardium
P wave
wave in an ECG that is caused as cardiac action potentials depolarize the cells of the atria
secondary pacemaker
the A-V node can also function as a _______ ______ if the S-A node should fail, however heart will typically only beat about 40-60 BPM as dictated by the rate of depolarization of the A-V node
second degree heart block
type of heart block when the cardiac conduction system transmits some, but not all of the action potentials. sometimes you will have P waves followed by a QRS complex, while other times you will not. most often due to severe damage to AV node or AV bundle
bundle of his
a group of large fibers that make up the A-V bundle which is where the impulses pass quickly through after they reach the distal side of the A-V node; the only electrical connection between the atria and ventricles
cardiac myocytes
name for heart muscle cells
interdigitating folds
interconnecting folds of the cardiac myocytes' cell membranes
mechanical junctions
strong proteins that bind adjacent cardiac myocytes, which prevents heart tissue from being torn apart as the heart beats
internodal pathways
impulse passes along _______ ________ of the conduction system that are continuous with atrial muscle fibers which lead to the atrioventricular node (A-V node)
interventricular septum
the muscular wall that separates the right and left ventricles
threshold
cells of the S-A node reach ________ on their own - membranes contract one another
junctional fibers
conduct the impulse into the A-V node; very small diameters so conduction is slow; delays impulse transmission; impulse is slowed as it passes A-V node allowing more time for the atria to completely empty and ventricles to fill before ventricular contraction
Atrioventricular node (AV node)
located in inferior portion of the septum that separates the atria.
cardiac muscle tissue
system is made up of clumps and strands of specialized ______ _______ _____ throughout the heart whose fibers contain only a few myofibrils
Sinoatrial Node (SA)
The sinoatrial node is located in the right atrium near the superior vena cava and is the primary pacemaker of the heart.
T wave
wave in an ECG that is caused as the cells of the ventricles go through repolarization of the cardiac action potential
third degree heart block
type of heart block when the AV node or AV bundle is not transmitting any action potentials at all. also called complete heart block. The SA node still depolarizes regularly, and triggers atrial depolarization, a P wave, and thus contraction of the atria. however none of these action potentials are carried to the ventricles.
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