Electrical And Molecular Mechanisms

Question 1

Which ion is responsible for the resting membrane potential of a cell?

Answer 1

K+ ions

Question 2

What are the concentrations of K+ on the inside and outside of the cell?

Answer 2

Inside = 150mM
Outside = 5mM

Question 3

What is the resting membrane potential of a cell?

Answer 3

Around -90 mV

Question 4

Define equilibrium in regards to an ions movement.

Answer 4

Where it’s concentration gradient and electrical gradients are matched

Question 5

What is the first step in a ventricular action potential?

Answer 5

The opening of voltage-gated Na+ channels

Question 6

What happens to a voltage-gated Na+ channel after it has opened?

Answer 6

It becomes inactivated

Question 7

What ion is responsible for the plateau phase of a cardiomyocyte action potential?

Answer 7

Entry of Ca2+ ions

Question 8

What type of Ca2+ ions are found in ventricular cardiomyocytes?

Answer 8

L-type Ca2+ voltage-gated channels

Question 9

What ion is responsible for repolarisation of a cardiomyocyte?

Answer 9

Entry of K+ ions

Question 10

Define sinus rhythm.

Answer 10

Any cardiac rhythm where depolarisation begins at the SA node

Question 11

What part of the heart is quickest to depolarise?

Answer 11

Cardiomyocytes at the SA node

Question 12

What is the resting membrane potential of cardiomyocytes at the SA node?

Answer 12

They don’t have one

Question 13

What can the depolarisation of the Na+ channels be described as?

Answer 13

Slow - the funny current

Question 14

What is the slow depolarisation of Na+ channels at the SA node called?

Answer 14

The pacemaker potential, or the funny current

Question 15

From what voltage does depolarisation of Na+ channels at the SA node begin?

Answer 15

-60mV

Question 16

What type of Na+ channels are located at the SA node?

Answer 16

HCN channels

Question 17

Are the HCN channels at the SA node voltage-gated?

Answer 17

No

Question 18

What activates the HCN channels at the SA node?

Answer 18

Hyperpolarisation

Question 19

How does increasing negativity at the SA node affect the HCN channels?

Answer 19

Increasing negativity causes an increase in the number of HCN channels that open

Question 20

Why does the SA node set the rhythm of the heart?

Answer 20

It is the quickest to depolarise

Question 21

What does the Nernst equation describe?

Answer 21

The equilibrium potential of a particular ion (I think)

Question 22

What term describes action potentials that fire too quickly?

Answer 22

Tachycardia

Question 23

What term refers to action potentials firing too slowly?

Answer 23

Bradycardia

Question 24

What range is extracellular K+ concentration kept within?

Answer 24

3.5-5-5mmol/L

Question 25

What term describes electrical activity that has become random?

Answer 25

Fibrillation

Question 26

Why are cardiomyocytes so sensitive to changes in K+ concentrations?

Answer 26

Cardiomyocytes have a negative resting membrane potential close to the equilibrium potential of K+