Conduction system of the heart Flashcards
Name the conduction system in order starting at the top?
- ) Sinus Node
- ) AV Node
- ) AV bundle
- ) Left & Right bundle branch
- ) Purkinje Fibers
Cardiac Muscle
Elongated, branching cells containing 1-2 centrally located nucl
Cardiac Muscle contains ?
- actin and myosin
myofilaments
Intercalated disks
Specialized Cell - Cell contacts
Desmosomes
hold cells together
allow action potentials to move from one cell to the next
Gap junctions
Electrically, cardiac muscle of the atria and of the ventricles behave as ?
Single Unit
Cardiac Mitochondria comprise
30% of volume of the cell
Skeletal Mitochondria comprise
2 % volume of the cell
Cardiac action potential
conducted from cell to cell
Skeletal action potential
conducted along the length of a single fiber
Rate of Action Potential Propagation
in CARDIAC muscle?
Slow because of gap junctions and small diameter of fibers.
Rate of Action Potential Propagation
in SKELETAL muscle?
Faster due to larger diameter fibers.
CICR
Calcium-induced calcium release
What stimulates release of Ca2+ from sarcoplasmic reticulum
?
Movement of extracellular Ca2+ through plasma membrane and
T tubules into sarcoplasm
Action potential in T-tubule
also stimulates Ca++ release from sarco-plasmic reticulum
Rising phase of action potential is due to ?
opening of fast Na+ channels
Plateau phase of action potential is due to ?
- Closure of sodium channels - Opening of calcium channels - Slight increase in K+ permeability - Prevents summation and thus tetanus of cardiac muscle
Repolarization phase of action potential is due to ?
- Calcium channels
closed - Increased K+
permeability (K+ out)
SA node sends conduction to what 2 structures?
AV node
Left Atrium
mV =
millivolts
SA node
The Pacemaker - Specialized cardiac muscle cells. - generate spontaneous action potentials -
AV node
- Action potentials conducted more slowly here than in any other part of system.
- Ensures ventricles receive signal to contract after atria have contracted
passes through hole in cardiac skeleton to reach interventricular septum
AV bundle
extend beneath endocardium to apices of right and left ventricles
Right and left bundle branches
- Large diameter cardiac muscle cells with few myofibrils.
- Many gap junctions.
- Conduct action potential to ventricular muscle cells (myocardium)
Purkinje fibers
Depolarization of SA Node has ?
no stable resting membrane potential
Pacemaker potential
gradual depolarization from -60 mV, slow influx of Na+
At what threshold does Action potential
occur?
-40 mV
depolarizing phase to 0 mV is a result of what ?
fast Ca2+ channels open, (Ca2+ in)
repolarizing phase is a result of what ?
- K+ channels open, (K+ out) - at -60 mV K+ channels close, pacemaker potential starts over
Each depolarization creates
1 hearbeat
SA node at rest fires at 0.8 sec, about
75 bpm
In the Sequence of Excitation, the Sinoatrial (SA) node generates impulses about _____
75 times/minute
In the Sequence of Excitation, the Atrioventricular (AV) node
delays the impulse approximately 0.1 second
Impulse passes from atria to ventricles via the
> AV bundle (Bundle
of His)
Purkinje Fibers
Myocardial fibers
depolarization of atrial myocardium.
Signals onset of atrial contraction
P wave
Ventricular depolarization
QRS Complex
Repolarization of the ventricles
T wave
length of time for the PR interval or PQ interval?
0.16 sec
a PR interval or PQ interval > than 0.20 sec (200 msec) indicates what ?
Damage to the conducting pathway or AV node has occurred
time required for ventricles to undergo a single cycle of depolarization and repolarization
Q-T interval
What can lengthen Q-T interval ?
- electrolyte disturbances
- conduction problems
- coronary ischemia
- myocardial damage
Internodal pathways are located in the ?
RA
Conduction System pathway from SA - AV in milliseconds?
.03 msec
Conduction System pathway from AV - Bundle branch in milliseconds?
.17 msec
Conduction System pathway from bundle branch - purkinje fibers in milliseconds?
.21 msec
