Heart electrophys Flashcards by Marissa Bobay

3 functional categories of cardiac myocytes

contracting cells
conducting cells
pacemaker cells

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locations for conducting cells in heart

His/Purkinje system
Bundle branches

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locations for pacemaker cells in heart

SA node
AV node

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location of contractile cells in heart

walls of atria and ventricles

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pacemaker cells are a subtype of what kind of other cell?

conducting cells

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rate of conduction at AV node,
size of cells,
channel used

slow AP

small cells

slow response AP phase 0 thru L-type Ca2+ channels

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rate of conduction at His/Purkinje system,
size of cells,
channel used

FAST AP

large cells

fast response AP phase 0 thru voltage-gated Na+ channels

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AV node function

slows conduction so atria have time to contract before signal goes to ventricles

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His/Purkinje system function

gets depolarization signal to apex of heart faster + allows contraction from apex to base

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slow response AP at phase 0 / fast response AP at phase 0 are controlled by what

autonomic NS:

sympathetics = increase phase 0 conduction
parasympathetics = decrease phase 0 conduction

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FAST AP velocity with:

-diameter of cell
-# gap junctions
-current
-rate of membrane depol
-density of open voltage-gated channels

-LARGE diameter of cell
-MANY gap junctions
-LARGE current
-FAST rate of membrane depol
-HIGH density of open voltage-gated channels

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AP conduction velocities:

SA node -> AV node
AV node -> bundle of His
bundle branches -> Purkinje fibers
Purkinje fibers -> contractile myocytes

0.5-0.8 m/s

0.05 m/s

2-4 m/s

0.5-1 m/s

(diagram in notes page 4)

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conduction pathway in heart (5 places)

SA node
AV node
Bundle of His
Left/Right bundle branches
Purkinje fibers

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slow AP produced by which cells and located where

pacemaker cells in SA and AV nodes

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fast AP produced by which cells and located where

conducting cells in His/Purkinje & bundle branches
AND
contractile cells in walls of atria & ventricles

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what substances do contractile cells contain

actin and myosin

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define autorhythmic and give an example of cells that are autorhythmic

-contraction of the heart comes from the heart itself (without need for external signal)

conducting cells

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since conducting cells are autorhythmic, they don’t have what?

actin and myosin

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cardiac myocytes

-form what
-are what -> due to what

-functional syncytium
-electrically coupled due to gap junctions within intercalated discs

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all cardiac myocytes are what

excitable

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phases of a fast AP

phase 0
phase 1
phase 2
phase 3
phase 4

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fast AP

phase 0- _____
phase 1- _____
phase 2- _____
phase 3- _____
phase 4- _____ (contractile/normal conducting cells)

0- initial depol
1- initial (brief) repol
2- plateau
3- repol
4- resting membrane potential

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slow AP

phase 0- _____
phase 3- _____
phase 4- _____

0- initial depol
3- repol
4- spontaneous depol

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phase 4- _____ (in contractile cells)
or
phase 4- _____ (in pacemaker cells)
or
phase 4- _____ (in His/Purk conducting cells only)

4- resting membrane potential (contractile cells)
or
4- spontaneous depol (pacemaker cells)
or
4- gradual depol (His/Purk conducting cells only)

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fast response APs -membrane potential -speed of phase 0 depol -other phase

-90 mV resting membrane potential fast phase 0 depol plateau phase 2 (prolongs AP)

fast AP phase 0 initial depol caused by what forces

Na+ influx

fast AP phase 2 plateau caused by what forces

both Ca2+ influx (depol) and K+ efflux (repol)

fast AP phase 3 repol caused by what forces

K+ efflux

length of ERP in fast response AP and why

ERP is LONG bc long-acting L-type Ca2+ channels open for so long

define ERP

effective refractory period -time when no new AP can be generated / propagated

how does ERP benefit the heart

protects heart from producing extraneous beats

what causes Ca2+ influx for fast AP phase 2

L-type voltage-gated Ca2+ channels opening

3 states possible for voltage-gated Na+ channels

open closed inactive

fast AP Na+ channels triggered to open by

temporary depol

(fast AP) what is the membrane classified as when all Na+ channels have inactivated?

"refractory" (incoming stimulus doesn't produce AP)

(fast AP) how do inactive Na+ channels become ready to be opened again? what is this time period called?

they reset overtime as membrane potential repol as they are resetting = "relative refractory period"

what happens to an AP produced during the "relative refractory period"

it is smaller bc only a few channels have reset by this time

slow response APs -what phases does it not have -what happens at phase 4 -resting potential is _____ -AP duration vs fast AP

no phase 1 or 2 (plateau) phase 4 spontaneous depol (up to threshold) unstable resting membrane potential AP duration shorter than fast AP

define automaticity

ability to generate AP due to spontaneous depol

slow AP phase 0 depol caused by what forces

L-type Ca2+ channels open, Ca2+ influx

slow AP phase 3 repol caused by what forces

L-type Ca2+ channels inactivate, K+ channels opening

slow AP phase 4 spontaneous depol caused by what 4 forces

L-type Ca2+ channels open HCN (funny) channel opens, Na+ influx T-type Ca2+ channels open K+ channels closing

under what condition can HCN (funny) channel open

when membrane repol to at least -60 mV

what node is the "primary pacemaker" of the heart and why

SA node, sets HR

what cells have automaticity

all of them (as back-ups to SA node)

SA node intrinsic firing rate (AP/min)

60-100

AV node intrinsic firing rate (AP/min)

40-80

Bundle of His intrinsic firing rate (AP/min)

Purkinje fibers intrinsic firing rate (AP/min)

15-20

define "overdrive suppression"

AP coming from upstream (i.e. SA node) overrides any other AP activity downstream - immediately brings all cells downstream to threshold + beat in sync

parasympathetics cause _____ secretion and _____ HR

(vagus n.) ACh decreases HR

sympathetics cause _____ secretion and _____ HR

norepi increases HR

order of contraction for parts of heart

1) atria 2) apex 3) rest of ventricle (squeezes up like toothpaste -> towards AV junction)

_____ released by sympathetics, binds to _____ receptors

norepi beta1 adrenergic

beta1 adrenergic receptor binding affects on chronotropy / dromotropy

beta1 stimulates chronotropy / dromotropy

_____ released by parasympathetics, binds to _____ receptors

ACh M2 muscarinic cholinergic

M2 muscarinic cholinergic receptor binding affects on chronotropy / dromotropy

M2 muscarinic cholinergic inhibits chronotropy/ dromotropy

which cardiac myocytes express beta1 adrenergic receptors

contractile conducting pacemaker

GPCR that activates beta1 adrenergic receptors

Gs (stimulatory)

GPCR that activates M2 muscarinic cholinergic receptors

Gi (inhibitory)

chronotropy affects _____

dromotropy affects _____

conduction velocity

effects on the pacemaker potential are primarily due to _____

the HCN (funny) channel

sympathetics chronotropic/dromotropic affects on slow APs

norepi = positive (+) chronotrope, dromotrope (increases HR, conduction velocity)

parasympathetics chronotropic/dromotropic affects on slow APs

ACh = negative (-) chronotrope, dromotrope (decreases HR, conduction velocity)

mechanism for positive chronotropic effects of norepi on slow APs

mechanism for positive dromotropic effects of norepi on slow APs

mechanism for negative chronotropic effects of ACh on slow APs

mechanism for negative dromotropic effects of ACh on slow APs

dromotropic effect of HCN (funny) channel

(cAMP binds to HCN) increase in cAMP = increase in conduction velocity

chronotropic effect of HCN (funny) channel

(cAMP binds to HCN) increase in cAMP = Na+ influx = spontaneous depol (increases HR)

draw autonomic effects of HCN (funny) channel

3 causes of increased SA node firing rate (increases HR)

sympathetic NS activity epi hypokalemia (decrease K+ in ECF)

3 causes of decreased SA node firing rate (decreases HR)

parasympathetic NS activity hyperkalemia (increase K+ in ECF) old age good physical fitness

how to calculate max HR attainable

220 bpm - age in years

SA node -function -symp stimulation is a _____ -parasymp stimulation is a _____

pacemaker symp = (+) chronotrope parasymp = (-) chronotrope

AV node -function -symp stimulation is a _____ -parasymp stimulation is a _____

slows down AP conduction between atria + ventricles symp = (+) dromotrope parasymp = (-) dromotrope

SA node and AV node -cell type -produce what kind of AP -innervated by what

nodal cells produce slow APs innervated by symp + parasymp

Map of cell types, AP types, stability of electrical locations on heart

K+ leak channel, phase, responsible for

L-type Ca2+ channel, phase, responsible for

T-type Ca2+ channel, phase, responsible for

(fast) voltage-gated Na+ channel, phase, responsible for