Test 1: Wk2: 4 Cardiac Electrophysiology - Puri Flashcards
1
Q
at rest the cardiac myocyte is only permeable to
A
K+
2
Q
at rest the cardiac RMP =
A
Nernst potential for K+
3
Q
potential is reliant upon — concentration inside and outside the cell
A
K+
4
Q
depol — probability of both open and inactive channels
A
increases
5
Q
repolarization induces recovery from — to —
A
inactive to closed
6
Q
the number of cation channels available for the next cycle and there readiness depends on
A
RMP
7
Q
Outward rectifiers
A
open as the membrane depolarizes, K+ rapidly repolarizes the cell
8
Q
Inward rectifiers
A
open at rest and allow K+ to leave cell when Vm
9
Q
what direction does K+ always go in
A
leaves the cell
10
Q
phase 0
A
rapid upstroke - depol of cardiac muscles
11
Q
phase 1
A
initial repolarization
12
Q
phase 2
A
stabilization of membrane potential - plateau phase
13
Q
refractory period
A
duration of phase 2
14
Q
phase 3
A
rapid repolarization
15
Q
phase 4
A
return to resting membrane potential
16
Q
phase 0 ions
A
Na in
K x
17
Q
phase 1 ions
A
K out
18
Q
phase 2 ions
A
Ca in
K out
19
Q
phase 3 ions
A
Ca x
K out
20
Q
phase 4 ions
A
K open but no outward movement of K when equilibrium is reached
Na/ATPase restores balance
21
Q
— drive repolarization and remain open from phase — to —
A
outward rectifiers
1 3
22
Q
— close as the Vm approaches 0 and the action potential is made possible
A
inward rectifiers
23
Q
— sodium channels are the main targets of antiarrhythmic drugs
A
SCN5A
24
Q
Na channels open when mV =
A
-70
25
Na channels have ---
time dependent inactivation
26
reactivation of Na channels requires almost complete --- of Vm
repolarization
27
--- Ca channels are critical for --- cardiac contraction
L type
initiating
28
--- open slowly as the membrane depol and remain open until --- mV
delayed outward rectifiers
-70
29
--- open when mV reaches --- and remain open at rest
inward rectifiers
-60
30
absolute refractory period
inactivation of fast Na channels
31
relative refractory period -
the action potential has
some Na channels recover to closed state and cane be activated at higher than normal threshold
reduced conduction velocity
32
Supernormality
the action potential is
threshold for activation is lower than resting cardiac myocyte
still slow
33
the duration of refractoriness depend on the --- and --- of the repolarizing current via ---
strength and rapidity
K+
outward rectifiers
34
P wave represents
atrial deopl
35
QRS complex is produced by
the summed up phase 0 ventricular myocytes action potentials
36
QRS complex is wider when
velocity is decrease
37
ST segment corresponds to
the plateaus of the action potentials
38
ST segment is dependent on balance of
incoming Ca and outgoing K
39
T wave is produced by
ventricular repol
40
T wave depends on
strength of outward K current
41
QT interval is the
action potential duration
42
TP segment is phase --- of the ---
phase 4 of fast action potential
43
many antiarrhythmic drugs target
fast Na channels
44
lidocaine
delay recovery of fast Na channels from inactivation at -65
| SCN5A recover at -80
45
quinidine, amiodarone
prevent or delay SCN5A opening - slowing upstroke of fast action potential
46
amiodarone
interrupt cardiac rythym
| prolong the ERP - K+ channel blockers
47
verapamil
Ca channel blocker
| reduce strength of cardiac contraction -0 shorten ERP
48
action potential in the nodes have no
phase 1 or 2
49
Nodes phase 0
opening of L Ca channels ➡ Ca mediated inward current
50
Nodes Phase 3
Kr and Ks channels open ➡ mediated inward current
51
Nodes resting membrane potential
less negative - fewer K open
52
phase 4 autonomic depol
funny current
53
what is the natural pacemaker of the heart, why
SA node
| highest density of HCN channels
54
HCN channel order of density
SA > AV > His-Purkinje
55
SNS Control of HR
beta adrenergic stimulation increases Gas and increases cAMP and PKA
56
SNS Control of HR
| increases HCN activity ➡
⬆ slope of phase 4 depol
57
SNS Control of HR
| lower threshold for opening of
L Ca channels
58
SNS Control of HR
| faster opening of L Ca channels ➡
⬆ slope of phase 0
59
SNS Control of HR
| faster repol vie increased Ik currents ➡
⬆ slope of phase 3
60
PNS Control of HR
| PNS stimulation activates --- and reduces --- ➡ ⬇ --- phosphorylation ➡ ---
Gi
cAMP
HCN
slower phase 4 depol
61
PNS Control of HR
↓ --- → ↓ --- phosphorylation → higher threshold for --- channel opening
and ---
↓ cAMP → ↓ L-type phosphorylation → higher threshold for Ca++ channel opening
and slower phase 0 depolarization
62
PNS Control of HR
| Stimulation of --- rectifiers --- the resting membrane Vm
Stimulation of KAch inward rectifiers lowers the resting membrane Vm
63
-- tone is the predominant tone regulation resting HR
parasympathetic
64
Automatic phase ---depolarization of the SA node predominate, and spread to the left atria via the ---
Automatic phase 4 depolarization of the SA node predominate, and spread to the left atria via the Bachman’s bundle
65
--- is the first to depolarize
Right atria is the first to depolarize → depolarization
spread from right to left, and downwards towards the
AV node–this is sinus rhythm
66
--- nodes depolarizes the bundle of His which divides
| into --- in the septum
AV nodes depolarizes the bundle of His which divides
| into left and right branches in the septum
67
depolarization in the septum spreads from --- to ---
depolarization in the septum spreads from left to right
68
--- terminate in Purkinje fibers, which
| make contacts with myocardial cells
Bundle branches terminate in Purkinje fibers, which
| make contacts with myocardial cells
69
Depolarization spreads across the --- by
| myocardial cell-to-cell conduction
Depolarization spreads across the ventricles by
myocardial cell-to-cell conduction → spread across
ventricles is more or less uniform
70
--- facilitate cell-cell transmission of the cardiac ---
Gap junctions facilitate cell-cell transmission of the cardiac action potential
71
structure or gap junctions
formed by the interaction of the connexons of two neighboring cells
72
Connexon
composed of six membrane-spanning proteins (connexins) with a central pore
In cardiomyocytes
73
connexons control
control the passage of electrical stimulus
74
The impulse from the --- node depolarizes the resting cardiac myocyte
The impulse from the SA node depolarizes the resting cardiac myocyte
75
How does the electrical
| impulse propagate?
see slide
76
current sink
Positive charges from the membrane ahead of the
action potential flow into the area of negative charge
represented by the action potential
77
what causes current sink
due to the flow of electrons on
| either side of the membrane
78
Speed of impulse propagation is termed
conduction velocity
79
--- have the slowest conduction
| velocity in the heart
Nodes have the slowest conduction
| velocity in the heart
80
Na/Ca exchanger is
bidirectional
81
Na/Ca exchanger # Na exchanged for # Ca
3 Na for 1 Ca
