Electrical Activity of the Heart Flashcards
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
12
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
