Origin of membrane potentials

Question 1

Membrane potential (Em)

Answer 1

separation of opposite charges across the membrane

Question 2

what does potential mean?

Answer 2

the ability to do work

Question 3

What actually is Em? if not a charged membrane?

Answer 3

The difference in charge in the extracellular fluid and intracellular fluid

Question 4

Which cells are excitable cells?

Answer 4

nerve and muscle cells

Question 5

What do excitable cells do?

Answer 5

rapidly and transiently alter their permeability in response to appropriate stimulation, results in Em fluctuations

Question 6

Resting membrane potential

Answer 6

Cells at rest, constant in non-excitable cells

Question 7

What causes resting membrane potential?

Answer 7

unequal distribution of ions with selective movement through the membrane.

Question 8

What Ions are unequally distributed? and where?

Answer 8

Na+ is higher outside the cell, gradient is inwards
K+ is higher outside the cell, gradient is outwards

Question 9

Which ion has a leak channel?

Answer 9

both, but potassium has a greater amount

Question 10

Are Na+ and K+ cations or anions?

Answer 10

cations

Question 11

Which Ion is the membrane impermeable to?

Answer 11

negatively charged intracellular proteins

Question 12

Equilibrium potential

Answer 12

When the concentration gradient and electrical gradient of an ion balance out, no net movement

Question 13

Membrane potential at Ek

Answer 13

-90mV

Question 14

Membrane potential at ENa

Answer 14

+60mV

Question 15

Nernst equation

Answer 15

E_ion=61log₁₀ [ion₀]/ [ion₁]

Question 16

K+ and Na+ effects on resting membrane

Answer 16

Cell is negative at rest ~ -70mV
relatively large net diffusion of K+ outwards
relatively small net diffusion of Na+ inward - neutralises some of the potential created by K+ alone

Question 17

Goldman-Hodgkin-Katz (GHK) Equation

Answer 17

E_m=61log₁₀ (P_K+[K⁺]₀ + P_Na+[Na⁺]₀)/(P_K+[K⁺]_i + P_Na+[Na⁺]_i)

Question 18

When Pk+ =1 in the GHK equation, what dies PNa+ equal?

Answer 18

0.01

Question 19

What Em value do you use to plug in values for ion concentration

Answer 19

-83mV

Question 20

Sodium potassium pump

Answer 20

maintains concentration gradients
3 sodium out for every 2 potassium in
generates hyperpolarizing current (inside is more negatively charged)