# Membrane+Action potentials Flashcards

1
Q

Flux def

A

The number of molecules that cross a unit area per unit of time (number of particles).
i.e. molecules.m−2.s−1

2
Q

Equilibrium potential def

A

Equilibrium potential: the potential at which electrochemical equilibrium has been reached. It is the potential that prevents diffusion of the ion down its concentration gradient

3
Q

What are the most important ions for determining a neurons resting potential?

A
4
Q

What does the nernst equation describe?

A

Used to calculate equilibrium potential using temp and ion concentrations

4
Q

What is the Goldman-Hodgkin-Katz (GHK) equation and what does it describe?

A

The GHK equation describes the membrane potential (Em) using ion permeability and concentration more accurately; P is permeability or channel open probability (0 = 100% closed, 1 = 100% open, 0.5 = open 50% of time), Subscript on P indicates the ion,
[K+], [Na+] and [Cl-] represent concentration and the subscript i or o indicates inside or outside the cell.

5
Q

What is proportional to each ions’ contribution to membrane potential?

A

Each ion’s contribution to membrane potential is proportional to how permeable the membrane is to the ion at any time.

6
Q

Calculate membrane potential at:
All channels are open all the time (PK = 1, PNa = 1, PCl = 1

A

Em = -61 * log((1[0.15] + 1[0.01] + 1[0.11])/(1[0.005] + 1[0.15] + 1[0.005]) )
= -61 * log(0.27 / 0.16)
= -61 * 0.225
= -14 mV

7
Q

Calculate membrane potential at:
K+ channels open, Cl- and Na+ channels closed (PK = 1, PNa = 0, PCl = 0)

A

Em = -61 * log ((1[0.15] + 0[0.01] + 0[0.11]) / (1[0.005] + 0[0.15] + 0[0.005]))
= -61 * log(0.150 / 0.005)
= -61 * 1.477
= -90 mV (Ion concentration has not changed BUT Em moved to EK)

8
Q

What does depolarisation, repolarisation, overshoot and hyperpolarisation mean?

A
9
Q

How does the size of an action potential change as it travels along an axon and why?

A
10
Q

How are the variety of nerve stimulations differentiated?

A

-Some depolarise, some hyperpolarise, controlling what happens next

11
Q

Do ion pumps control the change in membrane potential during an action potential?

A

NO

12
Q

What is the permeability of ions(Na+,K+) like at resting potential and why?

A

PK > PNa

Membrane potential nearer equilibrium potential for K+ (-90mV) than that for Na+ (+72mV)

13
Q

What occurs at the start of threshold potential?

A

K+ channels start opening slowly(Pk increases)-Still less than Na+ leaving the axon so potential is still becoming more positive

14
Q

What must happen for an action potential to be generated?

A

The membrane must reach threshold potential

15
Q

How does the release of K+ at an action potential vary with distance from the site of depolarisation?

A
16
Q

Where are voltage gated channels mostly located on myelinated axons?

A

Nodes of ranvier

17
Q

What factors increase/decrease conduction velocity?

A
18
Q

How does hyperkalaemia affect an action potential curve?

A

Resting potential is more positive, so easier to reach a threshold potential-but retains the same peak voltage on the upstroke

19
Q

How does hypernatraemia affect an action potential curve?

A

Hypernatraemia increases the amount of sodium efflux that occurs, so a larger upstroke occurs.