Membrane Potentials At Rest

Question 1

What is a membrane potential

Answer 1

A potential gradient that forces ions to move in one direction

Question 2

How are ionic concentration gradients maintained across the plasma membrane

Answer 2

-semi permeable membrane contains leak channels and voltage gated channels
-at rest potassium moves from inside to outside the cell down its chemical gradient via leak channels
-as it moves out it creates a negative charge inside the cell causing potassium to move in via its electrochemical gradient which determines resting potential
-Na+K+ATPase maintains high concentration of K+ inside cell and maintains gradient
-number of leak channels is what determines resting potential

Question 3

What is the electrochemical gradient

Answer 3

This is when there’s a chemical and electrical gradient
-chemical gradient is caused when K+ moves out the cell from high to low concentration as there’s a high concentration of K+ inside the cell
-electrical gradient is caused by potassium leaving the cell which makes the inside of the cell more negative causing K+ to move back in through leak channels

Question 4

What does the Nernst equation calculate

Answer 4

Finds the equilibrium potential of ONE ion and only applies to ions that can cross the plasma membrane

Equilibrium potential=RT/zF ln [x]/[y]
R=gas constant (8.315 J/K/mol)
T=temp in K
Z=valence of ion
F=faradays constant (9.684x10^4 C/mol)
[x]/[y]=ion gradient

Question 5

What does the goldman equation calculate

Answer 5

Goldman equation calculates the membrane potential, takes into account all the different ions in the cell and their permeability to the cell

Membrane potential (V)=61log Pk[K+]+PNa[Na+]+PCl[Cl-]/Pk[K+]+PNa[Na+]+PCl[Cl-]
P=permeability for each ion

Question 6

How is the resting membrane potential determined

Answer 6

-determined by number of leak channels
(Permeability) present and open
-Na+K+ATPase only maintained concentration gradient

Question 7

What is the impact of extra cellular changes in ion concentration (ECF ion levels)

Answer 7

Hypokalemia=reduced K+ outside the cell, results in more K+ efflux outside the cell to maintain Ek ( cell becomes less excitable hyperpolarised)
Hyperkalemia=Increases K+ outside the cell, less drive to reach Ek, membrane becomes easier to depolarise and becomes more excitable

Question 8

Why is the resting potential mainly determined by K+

Answer 8

Because there is a higher permeability to K+ (more K+ leak channels)

Question 9

List the concentrations of ions in ICF at rest

Answer 9

[Na+]=low
[K+]=high

[Cl-]= low

Question 10

List the concentrations of ions in ECF at rest

Answer 10

[Na+]=high
[K+]=low

[Cl-]=high

Question 11

Why is active transport so important

Answer 11

-maintain normal ionic concentration
-essential intracellulaire activities e.g. transport solutes into cell
-basis of membrane potential
-determines cellular gradients of other ions and molecules

Question 12

What is equilibrium potential

Answer 12

Conc of ions across plasma membrane, dependant on permeability of ion

Each ion has a different equilibrium potential, it’s the potential difference across the membrane relates to a particular ion in equilibria

Question 13

Why are membrane potentials important

Answer 13

-changes to membrane potential from rest produce electrical signals
-action potentials