S1W1 L2 Electrical activity of the heart

Question 1

extracellular and intracellular conc of Na (mM)

Answer 1

140, 10

Question 2

extracellular and intracellular conc of K (mM)

Answer 2

4, 140

Question 3

extracellular and intracellular conc of Ca (mM)

Answer 3

1.2, 0.0001

Question 4

equilibrium potential/ Nernst potential

Answer 4

potential gradient across the membrane to maintain concentration gradient, calculated by Nernst equation, tells us what electrical potential is needed to stop diffusion of ions down their chemical gradient

Question 5

Na, Ca, K equilibrium potentials

Answer 5

+70mV
+12mV
-94mV

Question 6

So, if cell is held at -94mV,

Answer 6

no net K movement in or out of cell

Question 7

what is resting membrane potential

Answer 7

potential difference between the inside and outside of the cell, represents voltage difference inside and outside cell
result of differences in ion conc across membrane
sum of different ions equilibrium potential x electrical conductance

Question 8

what are the electrical properties of a tissue dependant on

Answer 8

which ion channels are expressed in the membrane

Question 9

when does the fast voltage gated Na+ channels open and effect

Answer 9

-70mV
activated and inactivated rapidly
inward membrane current generated

Question 10

two ion channels which move Na+ back out of the cell

Answer 10

Na+/K+ pump
Na+/ Ca2+ exchanger

Question 11

2 types of cardiac Ca2+ channels

Answer 11

T-type and L-type

Question 12

T type Ca2+ channel

Answer 12

tiny conductance and transient openings
opens at -55mV, inactivate fairly rapidly

Question 13

L type calcium channel

Answer 13

large conductance and long lasting openings
found throughout heart
open at -40mV and inactivate more slowly

Question 14

direction and effect of K current

Answer 14

outward
make cell more negative inside
helps with repolarisation

Question 15

why does K+ exert most control over resting and action potential duration

Answer 15

cell at rest is more permeable to K+

Question 16

three main K+ currents:

Answer 16

background K+ current
delayed K+ currents transient outward K+ currents

Question 17

what controls background K+ current

Answer 17

inward rectifying channel (Kir)
resting outward current (I kin/ Ik1)

Question 18

when do background K+ channels open and their function

Answer 18

• voltages
  help set stable - resting membrane potential of atria and ventricular myocyte

Question 19

when do delayed K+ current and transient outward k+ current channels close
and function

Answer 19

close at negative voltages
open when cell becomes more +
open to help repolarise cell after AP

Question 20

is the current voltage relationship for background current linear

Answer 20

no

Question 21

why do efflux of K+ ions not occur as cell becomes more positive past equilibrium potential

Answer 21

regulation by ion channel itself
magnesium ions
polyamines

Question 22

why is it important K+ doesn’t efflux out of cell

Answer 22

many consequences of K+ loss from cell

Question 23

background current ib

Answer 23

inward background current of mostly Na+
causes cell to be slightly higher than Ek

Question 24

funny current if

Answer 24

permeable to Na and K
activated at hyperpolarisation

Question 25

ventricular myocyte resting potential

Answer 25

-85/-90mV stable

Question 26

ventricular myocyte AP: what channels are open at negative potentials and set resting membrane potential close to Ek

Answer 26

ik1 ikir

Question 27

ventricular myocyte AP: what is the rapid depolarisation due to

Answer 27

opening of voltage gated Na+ channels

Question 28

ventricular myocyte AP: what channels close as Na+ permeability increases

Answer 28

background K+ channels

Question 29

ventricular myocyte AP: as cell becomes more positive due to Na+ influx, what channels transiently open

Answer 29

ito voltage gated K+ channels

Question 30

ventricular myocyte AP: what channels open when membrane potential reaches -40mV and effect

Answer 30

L type Ca2+ calcium enters cell causing plateau phase

Question 31

ventricular myocyte AP: when the cell is the most pearmeable to Ca2+, it is least permeable to

Answer 31

K+

Question 32

ventricular myocyte AP: what is repolarisation brought about by

Answer 32

K+ permeability increases ikr, iks voltage gated delayed K+ channels

Question 33

ventricular myocyte AP: when membrane potential is close to resting level, what occurs

Answer 33

background K+ channels open again to keep resting membrane stable

Question 34

conducting system AP: how is AP initiated

Answer 34

autorhythmic/ pacemaker cells

Question 35

conducting system AP: dominant pacemaker cell?

Answer 35

SAN

Question 36

SAN AP: why is there no stable resting membrane potential

Answer 36

background K+ channels are absent

Question 37

SAN AP: max diastolic potential?

Answer 37

-60mV

Question 38

SAN AP: what is known as pacemaker potential?

Answer 38

slow depolarisation towards threshold of -40mV

Question 39

SAN AP: three phases

Answer 39

upstroke repolarisation period between AP

Question 40

SAN AP: what four overlapping currents make up SAN AP

Answer 40

funny current (if) T type Ca2+ current L type Ca2+ current decay of delayed K+ channel permeability

Question 41

SAN AP: what currents are occurring in phase 4 (period between APs)

Answer 41

iCa (T) if

Question 42

SAN AP: what channels open at -40mV

Answer 42

L type Ca2+ depolarises cell

Question 43

SAN AP: what is repolarisation induced by

Answer 43

closure of L type Ca2+ channels opening of delayed K+ channels

Question 44

what is the pacemaker potential of the when SAN isolated

Answer 44

100 beats per min

Question 45

what is the pacemaker potential of the AVN when isolated

Answer 45

40 beats per min

Question 46

what is the pacemaker potential of the purkinje fibres when isolated

Answer 46

20 beats per min

Question 47

what cells can initiate a heartbeat

Answer 47

any cardiac cell with pacemaker ability

Question 48

how long does it roughly take for SAN to initiate AP in the rest of the heart

Answer 48

150-200ms

Question 49

what is the absolute refractory period of the SAN AP driven by

Answer 49

inactivation of Na+ channels, almost as long as contraction phase, can change depending on AP duration