Heart electrophys Flashcards
3 functional categories of cardiac myocytes
contracting cells
conducting cells
pacemaker cells
locations for conducting cells in heart
His/Purkinje system
Bundle branches
locations for pacemaker cells in heart
SA node
AV node
location of contractile cells in heart
walls of atria and ventricles
pacemaker cells are a subtype of what kind of other cell?
conducting cells
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
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
AV node function
slows conduction so atria have time to contract before signal goes to ventricles
His/Purkinje system function
gets depolarization signal to apex of heart faster + allows contraction from apex to base
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
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
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)
conduction pathway in heart (5 places)
SA node
AV node
Bundle of His
Left/Right bundle branches
Purkinje fibers
slow AP produced by which cells and located where
pacemaker cells in SA and AV nodes
fast AP produced by which cells and located where
conducting cells in His/Purkinje & bundle branches
AND
contractile cells in walls of atria & ventricles
what substances do contractile cells contain
actin and myosin
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
since conducting cells are autorhythmic, they don’t have what?
actin and myosin
cardiac myocytes
-form what
-are what -> due to what
-functional syncytium
-electrically coupled due to gap junctions within intercalated discs
all cardiac myocytes are what
excitable
phases of a fast AP
phase 0
phase 1
phase 2
phase 3
phase 4
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
slow AP
phase 0- _____
phase 3- _____
phase 4- _____
0- initial depol
3- repol
4- spontaneous depol
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)
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)
40
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 _____
HR
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
increase in cAMP
(cAMP binds to HCN)
increase in conduction velocity
chronotropic effect of HCN (funny) channel
increase in cAMP
(cAMP binds to HCN)
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
