# W4 Membrane and Action Potentials - Jason Potas Flashcards

1
Q

What is a membrane potential?

A

A potential difference of charge across a membrane. Maintained by Na+/K+ ATPase.

This potential difference is measured in Volts, V.

Resting Membrane Potential (RMP) is also known as Vm

2
Q

What is an action potential (AP)?

A

The ability of a voltage-gated ion channel to depolarise and repolarise.

3
Q

What is conductance, G of an ion?

A

The measure of ease with which an ion can cross a unit are of 1cm^2 of membrane.

Given by the equation:
G(ion) = Po.n.gamma

where:
Po = the probability that channel is open (i.e. a Po of 1 means that the channels are open all of the time.
n = the number of channels
gamma = the number of ions per sec that a channel can conduct.

4
Q

What is the Nernst potential?

A

The net effect of an ion wanting to move down its chemical gradient as well as its electrical gradient resulting in an equilibrium between the two forces as an electro-chemical gradient.

5
Q

What is the Nernst Equation?

A

A calculation of the Equilibrium potential, Ex, for the potential difference that would arise if the membrane was leaky to just one ion.

6
Q

What is the Goldman Equation?

A

A calculation for what the resting membrane potential should be.
Takes into account the relative conductance of the membrane of all ions as well as the electrochemical forces on each ion.

7
Q

Why is Na+ important in creating an action potential?

A

The opening of voltage-gated Na+ channels results in Na+ influx that leads to depolarisation of the membrane (i.e. RMP becomes more positive)

8
Q

What is the “Hodgkin-Huxley Cycle”?

A

The explosive upstroke of action potential and is associated with an increase in G(Na). (the increased conductance of Na+ into the cell)

9
Q

Why are K+ channels central for repolarisation?

A

K+ channels are slower to open than Na+ channels, but are longer lasting. They lead to an efflux of K+ out of the cell resulting in repolarisation (downstroke) of the AP.

10
Q

Define and state the mechanism behind absolute refractory period?

A

Absolute refractory period is the period when a second AP cannot be initiated. Due to the closed voltage-gated Na+ channels that must be “reset” by repolarisation.

11
Q

Define and state the mechanism behind relative refractory period?

A

Relative refractory period is the period where a second AP requires a stronger than normal impulse to be initiated. It is due to the leaky K+ channels that keep the membrane hyperpolarised.

12
Q

Why do different ion channels influence the shape of the action potential?

A

The channel properties and Nernst potential for each ion influences the AP shape. For example, cardiomyocytes also have Ca2+ channels, that affect the shape of the AP.