Resting Potential and Action Potential Flashcards Preview

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Flashcards in Resting Potential and Action Potential Deck (16):
1

Why do cells have an electrical potential?

Transmits information reliably + quickly over large distances
- controls Ca2+ entry into cells.
- Ca2+ is involved in gene regulation, growth and death

2

What is flux?

The number of molecules that cross a unit area per unit time.
At diffusion equilibrium there is no net flux.

3

Define Ohm's Law

Voltage = Current x Resistance

Voltage = Potential:
- Generated by ions to produce a charge gradient

Current:
- Movement of ions due to potential

Resistance:
- Barrier that prevents the movement of ions - cell membrane
- Permeability of membrane is key to the resting membrane potential

4

The resting membrane potential of excitable cells?

-70mV

- The Zero reference is placed outside the cell.
The inside of the cell is negative compared to the outside

- Resting potential is established by diffusion of ions through a selectively permeable membrane.

5

What are ion channels types?

Selective for different ions (K+,Na+,Cl-,Ca2+)

- voltage-dependent = open by change in membrane potential
- voltage-independent = open all the time, responsible for producing resting potential

6

What is Electrochemical Equilibrium?

This is when electrical forces balance concentration gradient, a stable membrane potential is established.

7

What is the Equilibrium Potential?

Potential that prevents diffusion down the ion's concentration gradient

8

What is the Nersnt Equation

A method of predicting the equilibrium potential for a given ion

Ex = (RT/ZF).ln(Co/Ci)

- Ex+ = equilibrium potential of ion X
- R = gas constant
- T = absolute temperature
- Z = charge on ion
- F = Faraday's number 96,500 coulombs of charge/mol of a singly charged ion
- Co = (X+) outside cell
- Ci = (X+) inside cell
- Substituting values of constants at 37oC

9

Using the Nernst Equation what is the Equilibrium Potentials of Potassium and Sodium?

- -92mV (K+) and +73mV (Na+)

- however this is not the real membrane potential.
- Also to consider is the permeability of the membrane to all ions
- POTASSIUM is the main ion which controls resting membrane potential

10

What is the Goldman-Hodgkin-Katz equation?

- derivation of the Nernst equation which includes membrane permeability.
- can manipulate the permeability of the membrane to various ions you can predict the resting potential.

11

Define the different changes in membrane potential?

Depolarisation - change in a positive direction
Overshoot - change from 0 in a positive direction
Repolarisation - change in a negative direction towards the resting potential
Hyperpolarisation - voltage drops below the resting potential.

12

What is a graded potential?

Graded Potentials:
-change in amplitude
- changes depending on stimulus
- bidirectional
- decrease in amplitde with increasing time and distance from origin
- They only occur at synapses + sensory receptors
- Function = generate/prevent action potential from forming.

Action Potential:
- uniform amplitude (all or nothing)

13

What are the 5 main phases of an action potential?

1 - resting membrane potential:
- membrane more permeable to K+ (RMP closer to equil of K+)
- Voltage-gated ion channels closed.

2- Depolarising stimulus:
- opens VGSCs
- membrane potential increases
- stimulus has to be above threshold to generate AP.

3- Upstroke/Depolarising phase
- starts at threshold potential
-increased membrane permeability to Na+
- Sodium moves into cell and mp increases to equilibrium potential
- VGKCs open much slower than VGSCs

4- Repolarisation
- VGCSs inactivated
- more VGKCs open - K+ leaves cell and membrane potential decreases back towards equil. potential to K+
- sodium inactivation gate closed
- k+ channel open
- no new AP generated

5- After-Hyperpolarisation
- VGKCs remain open for a few miliseconds (hyperpolarisation)
- inactivation gate open
- stronger than normal stimulus is required to trigger an AP = Relative Refractory Period

14

Describe Ion movements during the action potential?

- Very small changes in concentration during an AP
- Ion pumps not directly involved in ion movements during AP
- Electrochemical equil restored after AP by ions moving through NON VGICs

15

What affects the propagation of an Action Potential?

- diameter of neuron and myelination
- myelination = insulator so prevents loss of charge
- Absolute Refractory Period = blocks VGSCs by inactivation gate, hyperpolarised cant be depolarised.
- AP speed 120m/s

16

What increases the speed of an Action Potential?

- axon diameter
- myelinated

slowed by:
- cold
- anoxia
-compression
- drugs