Cardiac action potential

Question 1

Explain Phase 0 of the cardiac action potential

Answer 1

Rapid depolarisation
> Rapid sodium Influx
> sodium moves in

Question 2

Explain Phase 1 of the cardiac action potential

Answer 2

Early repolarisation
> Efflux of potassiumm
> Potassium and chloine moving out

Question 3

Explain Phase 2 of the cardiac action potential

Answer 3

Plateau
> Slow influx of calcium
> Calcium In, Potassium Out

Question 4

Explain phase 3 of the cardiac action potential

Answer 4

Final Reploarisation
> Potassium out

Question 5

Explain phase 4 of the cardiac action potential

Answer 5

Restoration of resting membrane potential (90 mV)
> Restore ionic concentrations
> Resting membrane potential is restored by Na+/K+ ATPase
> Slow entry of Na+ into the cell decreasing potential difference
> Threshold is reached
> Triggers a new action potential

Question 6

What are the fastest velocities in the heart?

Answer 6

Purkinje fibres

Question 7

At which part of the cardiac conduction pathway is there a short delay before the spread of the action potential continues?

Answer 7

AV node

Question 8

during the depolarisation phase which phases are open?

Answer 8

sodium, calcium

Question 9

Which ion channels are open during the plateau phase of the cardiac action potential?

Answer 9

Calcium + potassium

Question 10

Which ions are responsible for the generation of the “funny” current?

Answer 10

Sodium + potassium

Question 11

Which properties of cardiac muscle enable the propagation of action potentials?

Answer 11

Cardiac muscle is arranged in a syncytium

Question 12

In a non-pacemaker cardiac cells, which ion channels trigger depolarisation?

Answer 12

Voltage-gated sodium channels and voltage-gated potassium channels

Question 13

When the brain tells a muscle to move, it sends signals down neurones. These signals are called action potentials. They are the temporary shift in the neuron’s membrane potential caused by ions flowing in and out of the neuron causing it to depolarise, repolarise and then hyperpolarise.

Which ion movement occurs during the nerve action potential repolarisation phase?

Answer 13

Potassium efflux

Question 14

Summary of stages

Answer 14

0 - 70mV (threshold potential), it triggers the opening of sodium (Na+) channels in the cell membrane. Leads to rapid depolarisation and an influx of sodium. Also some calcium influx

1- Membrane reaches +40, triggers sodium to close, causes potassium channel to open and efflux of potassium

2- Potassium channels remain open leading to a further eflux. Calcium channels open, leading to influx of calcium

3- The calcium channel closes, whilst the potassium channel remains open. Rapid efflux of K+ ions causes a decrease in membrane potential

4- Sodium potassium pump restores resting membrane potential (-90) by pumping 3 Na+ ions out while 2 K+ ions move in, utilising energy from ATP