cardiac membrane potential workshop

Question 1

describe phase 0 of the action potential

Answer 1

fast rising phase

very large inward sodium current responsible for depolarisation

the rate of change Vm is very high

Question 2

describe phase I of the action potential

Answer 2

there is a small dip after the peak, inactivation of intracellular sodium and activation of intracellular calcium

Question 3

describe phase 2 of the action potential

Answer 3

plateau phase

maintained depolarisation around 0mV

calcium current intracellular, another depolarising current but slower acting than intracellular sodium

Question 4

describe phase 3 of the action potential

Answer 4

depolarisation phase, membrane potential returns to resting potential. there is an outward potassium current, so hyper polarising current

Question 5

describe phase 4 of the action potentials

Answer 5

resting potential between action potentials. intracellular sodium, potassium and calcium all low

Question 6

what causes the upstroke of the action potential?

Answer 6

influx of sodium

Question 7

what account for the rapid rise in the sodium ions current

Answer 7

voltage dependence of the sodium channel

Question 8

what explains the sustained of plateau phase of the action potential?

Answer 8

influx of calcium

Question 9

what accounts to the rapid rise of the calcium ion current?

Answer 9

the voltage-dependance of the calcium channel

Question 10

what accounts for the depolarisation phase of the action potential?

Answer 10

efflux of potassium inactivation of sodium and calcium channels

Question 11

why does potassium current decline at the end of the action potential?

Answer 11

voltage dependance od the potassium channel

Question 12

what does tetrodotoxin do to action potentials?

Answer 12

blocks action potentials by blocking the pore of sodium ion channels

Question 13

which phase does blocking calcium channels affect the most?

Answer 13

phase 2, by making the plateau more hyper polarisation (reduced the threshold) and shortening the action potential considerably

Question 14

What effect has verapamil had on the stimulus threshold? Why is this?

Answer 14

no effect on the stimulus threshold or on phase 0 pr phase 1 of the action potential

Question 15

What effect has verapamil had on the action potential waveform and on its rate of rise (dV/dt) during Phase 0?

Answer 15

only a slight reduction in the rate of rise of the action potential

Question 16

Which phases of the action potential does blocking K channels affect?

Answer 16

blocking potassium channels prolongs the plateau of the action potential (phase 2) increasing the duration considerably

Question 17

What effect has 4AP had on the stimulus threshold?

Answer 17

• no effect on the peak or rate of rise of the action potential (phase 0, 1)