Cardiac action potenitals

Question 1

What is electrophysiology?

Answer 1

The study of electrical properties of biological cells and tissues

Question 2

What is the resting membrane potential?

Answer 2

The voltage difference across the plasma membrane

Question 3

What is the average resting membrane potential of a cardiomyocyte?

Answer 3

-90 - -80mV

Question 4

What determines resting membrane potential?

Answer 4

Combination of electrochemical gradients

Question 5

Is the inside of the membrane positive or negative compared to the outside?

Answer 5

Negative

Question 6

Does K+ move into or out of the cell?

Answer 6

Out

Question 7

Do Na+ move into or out of cell?

Answer 7

In

Question 8

How is the resting membrane potential maintained?

Answer 8

All channels closed except some K+ channels allowing some K+ to leak out of the cell

Question 9

How does depolarisation occur?

Answer 9

Na+ channels open and Na+ move into the cell. more voltage gated Na+ ion channels open and depolarisation occurs

Question 10

What occurs during early repolarisation?

Answer 10

Na+ channels close.

K+ leaks out of the cell causing small repolarisation

Question 11

What occurs during the plateau phase?

Answer 11

Voltage gated L-type Ca2+ channels open and Ca2+ floods into the cell - this is balanced by the K+ leaving the cell so it plateaus

Question 12

What occurs in the muscle during plateau phase?

Answer 12

Ca2+ moves into the cell and causes sarcoplasmic reticulum to release more Ca2+ and contraction occurs

Question 13

How does repolarisation occur?

Answer 13

Ca2+ channels close and voltage gated K+ channels open. K+ leaves the cell and causes repolarisation

Question 14

How is the resting membrane re-established after the action potential?

Answer 14

2K+ in exchanged for 3Na+ out.

When re-established all channels close except leaky K+ channels

Question 15

When does the depolarisation stage occur in relation to the increase in pressure in the ventricle?

Answer 15

Just before the increase in the pressure

Question 16

What are the differences between contractile myocardium AP and pacemaking cell AP?

Answer 16

Pacemaking cell does not have a constant resting membrane potential
Depolarisation caused by Ca2+ not Na+
No plateau
Higher permeability of Ca2+

Question 17

Why is the resting membrane potential of pacemaking cell not constant?

Answer 17

Hyperpolarisation and cyclic nucleotide gated channels are not specific so allow Na+ and Ca2+ into the cell.
Causes resting potential to increase

Question 18

How does depolarisation occur in pacemaking cells?

Answer 18

T-type Ca2+ channels cause slow depolarisation before threshold (along with some leaking Na+)
T-type Ca2+ channels stimulate L-type Ca2+ channels.
L-type Ca2+ channels cause most depolarisation

Question 19

How does repolarisation occur in pacemaking cells?

Answer 19

K+ moving out of the cell

Question 20

What ion mainly contributes to depolarisation in myocytes?

Answer 20

Na+

Question 21

What ions contribute to plateau phase in myocytes?

Answer 21

Ca2+ and K+

Question 22

What channels contribute to pacemaking cells in cardiomyocytes?

Answer 22

Hyperpolarsiation and cyclic nucleotide gated channels

T-type and L-type Ca2+