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how are cardiac muscle cells in comparison to skeletal muscle cells?

short, mono or bi nucleated rather than multi-nucleated


what do cardiac muscles have at cell linkages

intercalated discs
-gap junctions
-desmosomes (macula adherens) anchor actin filaments at the end of the sarcomere


what do desmosomes have to prevent adjacent cells from being pulled apart

mechanical couplings


what are pacemaker cells features of

cardiac muscle and autostimulatory cells
-non contractile cardiac muscle


what are fast response action potentials
what are slow response action potentials

muscle and purkinje fibers
SA and AV nodes


what happens when an AP triggers an electical dischange

travels rapidly across the atrial and ventricular muscles regardless of whether its origin was fast or slow


for APs, what goes in and out

Na in
K out


what happens in phase 0 of cardiac muscle action potential
phase 1?
phase 2?
phase 3?
phase 4?

0-depolarization due to Na influx
1-initial repoloarization bc of K outflux
2-plateau bc transient increase, K outflux slows, Ca channel now open and flattens curve
3-repolarization: decrease influx Ca and incrase outflux K
4-resting potential/stead state of ion flow


what does an abs refractory period do?

ensures that cardiac muscle cells can't be tetanized


what does a relative refractory period do

period in which an action pot can be elicited w/ an increased inward current


why can an effective tetanic (muscle spasm) contraction not be produced

bc of the duration of the action pot, cardiac muscles relax b4 it can be activated again


what do catecholamines do

enhance ca movement and increase size of AP
by binding to B1 receptor
-also increase of phase 3 K conductance (norepinephrine)


what do B2 catecholamine receptors do
what do B1 receptors do

mediate relaxation of smooth muscle
receptors in the heart


you dont want to extend plateau phase too far in an increase of phase 3 K conductance or else it will interfere w/ waht

refractory period


what are ca channel blockers used to treat

arrhythmias and high bp by slowing the heart
-depress ca movement => smaller action pot


in SA node AP what is phase 1, 3, 4

0-depolarization due to ca influx
3-repolarization due to K outflux
4-accounts for the pacemaker activity; due to slow influx Na, which is turned on by repolarization


in phase 4 in SA node AP, why is it not flat

slow influx of Na
-will reach threshold and fire on its own


what happens after repoloarization of phase 4

starts immediately heading towards threshold again "unstable resting pot"


what happens when phase 4 of SA node reaches threhshold

Ca generates AP


what nerve hyperpolarizes the resting pot and decreases the slope and heart rate of phase 4
what increaes the slope and heart rate?

vagus nerve (acetylcholine)
sympathetic nerves (norepinephrine)


what does the electrocardiogram do

measure of the heart's electrical activity
-can detect abnormality in heart rhythm, size of heart, electrolyte imbalances, myocardial ischemia and infarction, drug effects


what does an ECG not sure

direct info about contractile performance


why is ECG called a dipole

bc whenever there is a discharge, there will be a separation of charges across the heart


what is the electrical pathway

SA => AV => bundle of His => bundle branches => post fascicles


what is the p wave of the ECG

rep depolarization of the SA node and atria
when atria repolarize, the wave is hidden in the QRS complex


what is the QRS complex in the ECG
PR interval?
QT interval?

rep ventricular depolarization
-time it takes AP to get from SA node through the atria and just beyond the AV not but not yet the ventricles
-contraction of ventricles


what is teh T Wave of ECG
U wave?

rep repolarization of the ventricles
dunno, sometimes seen after T wave


an ECG may run by having electrods in only 3 positions, what are tehy

right arm, left arm, leg


what potential change are you measuring btwn locations in einthoven's triangle

lead 1: RA to LA
lead 2: RA to leg
lead 3: LA to leg


what is einthoven's law

if the electrical potentials of any 2 of the 3 bipolar limb ECG leads are known, the 3rd can be determined mathematically from the 1st two by simply summing the 1st 2 (signs of leads must be observed)


where are chest leads connected to

the positive terminal of the ECG and the negative electrode is attached at the same time to the right arm, left arm, and left leg


for a standard 12 point, how many electrodes involved

10, only 6 across the chest
right and left arm
right and left leg


how many scenarios are there clinically where a cardiologist would be interested in analyzing a full ECG



what are some heart abnormalies detected with ECG X____X

1. right or left ventricle hypertophy
2 respiratory sinus arrythmia
3. sinus tachycardia
4. premature ventricular or atrial contraction
5. atrial fibrillation
6. ventricular fibrillation
7. heart block
8. right or left bundle branch block


what is the first sign of a myocardial infarction

inversion of T wave


what does a progression of ischemia in a myocardial infarction result in

elevation of S-T segment
-ST segment elevation myocardial infarction (STEMI)


what does a myocardial infarction lead to

development of Q waves in front of elevated S-T


waht is ischemia

restriction of blood flow


what is an infarct

an area of necrosis in a tissue or organ resulting from obstruction of the local circulation by a thrombus (blood clot) or embolus (blockage in blood vessel)


what is an inotropic modification

somethign with a + inotropic effect increases the contractile force of cardiac muscle


what is the treppe/bowditch phenomenon

gradual increase in muscular contraction follwoing rapidly repeated stimulation
-seen w/ rapid heart contractions
-each peak back to baseline b4 another


why do contractions gets stronger w/ time in treppe/bowditch phenomenon

ca doesnt have time to get sequestered back into the sarcoplasimc ret so overall concentration gets higher in cytosol
-results in a "positiive inotropic mod" or cardiac muscle contraction


what is digitalis
what does it inhibit

cardiac flycoside found in the foxglove plant
Na/K ATPase inhibitor => increased intracell Ca which gives a + inotropic effect


what is s1 and s2 and s3 and s4 in the cardiac cycle

s1- the 1st heart sound, due to the clower of mitral and tricuspic valves
s2-due to closure of pulmonary and aortic semilunar valves
s3 and s4-abnormal heart sounds for the gen pop