Electrical Activity of the Heart Flashcards
(44 cards)
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
