Cardiovascular - Electrophysiology

Question 1

What is the main driver of the membrane potential during Phase 0 of the cardiac myocyte?

Answer 1

Na⁺ influx through voltage gated sodium channels

Question 2

What is the main driver of membrane potential in Phase 1 of the cardiac myocyte?

Answer 2

transient K⁺ efflux

Question 3

What is the main driver of membrane potential in Phase 2 (Plateau phase) of the cardiac myocyte?

Answer 3

Ca²⁺ influx through voltage gated calcium channels (mainly L-type)

Question 4

What is the main driver of membrane potential in Phase 3 of the cardiac myocyte?

Answer 4

K⁺ efflux through voltage gated potassium channels

Question 5

What is the main driver of membrane potential in Phase 4 of the cardiac myocyte?

Answer 5

K⁺ influx

Question 6

What triggers the action potential of the cardiac myocyte?

Answer 6

Influx of Na⁺ and Ca²⁺ through gap junctions

Question 7

What happens at the threshold potential of the cardiac myocyte?

Answer 7

Voltage gated sodium channels are opened

Question 8

What is the threshold potential of the cardiac myocyte?

Answer 8

-70mV

Question 9

What happens when the maximum depolarization is reached of the cardiac myocyte membrane potential?

Answer 9

Voltage gated sodium channels close

Question 10

What is the maximum membrane potential reached in a cardiac myocyte?

Answer 10

30mV

Question 11

What causes repolarisation of the membrane potential of a cardiac myocyte?

Answer 11

Closing of voltage gated calcium channels and opening of voltage gated potassium channels

Question 12

Do the cells in the SinoAtrial node exhibit a stable resting membrane potential?

Answer 12

No, they exhibit spontaneous pacemaker potential.

Question 13

What is the pacemaker potential in a Sino Atrial node cell?

Answer 13

The slow depolarisation caused by decreased K+ efflux superimposed on a slow Na+ influx (funny current)

Question 14

What happens when the threshold membrane potential of a SinoAtrial cell is reached?

Answer 14

Opening of voltage-gated Ca²⁺ channels leading to the rising phase of action potential.

Question 15

What causes the falling phase (and repolarisation) of membrane potential in a SinoAtrial cell?

Answer 15

The opening of K⁺ channels, resulting in K⁺ efflux.

Question 16

How does the action potential spread between cells in the atria?

Answer 16

Gap junctions

Question 17

How does the action potential spread from the SA node to the AV node?

Answer 17

Mainly gap junctions but also some internodal pathways

Question 18

What is the consequence of conduction being delayed in the AV node?

Answer 18

It allows atrial systole to precede ventricular systole.

Question 19

How does the action potential spread to the ventricles?

Answer 19

Along the bundle of His and the Purkinje fibres.

Question 20

How does the action potential spread through the ventricles?

Answer 20

Cell to cell conduction (gap junctions)

Question 21

What is autorhythmicity?

Answer 21

The ability of the heart to beat rhythmically in the absence of external stimuli.

Question 22

What is the funny current?

Answer 22

A depolarising current mediated by channels that are activated by

1. hyperpolarisation
2. cyclic AMP

These are known as HCN (Hyperpolarization-activated Cyclic Nucleotide gated) channels.

Question 23

How does the action potential cause ventricular contraction?

Answer 23

Cytoplasmic Ca²⁺ binds to troponin C, causing cross bridge formation between action and myosin.

Question 24

What triggers cardiac muscle relaxation?

Answer 24

Voltage activated Ca²⁺ channels close, and Ca²⁺ leaves the cell through the Na⁺/Ca²⁺ exchanger (NCX).

Ca²⁺ reuptake into sarcoplasmic reticulum.

Ca²⁺ dissociates from troponin.

Cross bridge between actin and myosin break, causing relaxtion.