Membrane Potential

Question 1

Qualitatively compare Na+ and K+ concentration intracellularly vs extracellularly

Answer 1

Na+ concentration is far greater extracellularly while K+ is far greater intracellularly

Question 2

Qualitatively compare Ca2+ concentration intracellularly vs extracellularly

Answer 2

Far higher concentration extracellularly

Question 3

Describe the measurement of membrane potential

Answer 3

Using intracellular microelectrodes and comparing it with the extracellular voltage

Question 4

What creates membrane potential (Vm)

Answer 4

Difference of electric charges

e.g. -70mV intracellularly, 0mV out creates a -70mV Vm

Question 5

What factors affect ion movement across the plasma membrane

Answer 5

Concentration gradient, Voltage

Question 6

How does voltage affect ion movement

Answer 6

Cations are attracted to move in the direction of negative voltages and anions are attracted to positive voltages

Question 7

Diffusion Potential

Answer 7

Voltage at which the electrostatic force on an ion is equal and opposite to the chemical force from the concentration gradient

It is a steady state of electrochemical equilibrium - no net force/net ion flow, change in ion concentration or Vm

Question 8

How do Na+ and K+ move across membranes

Answer 8

Facilitated Diffusion

Question 9

Notation of K+’s diffusion potential

Answer 9

E_K (Nernst Potential)

Question 10

Nernst Equation

Answer 10

E_K(i-o)=61Log₁₀([K⁺]_o/[K⁺]_i)

Used to calculate diffusion potential to maintain a certain concentration gradient/difference

Question 11

Voltage when cell membrane is solely permeable to K+

Answer 11

V_m=E_K

Question 12

Example of a membrane potential which is Nernstian in behaviour (well described by Nernst equation)

Answer 12

Some types of skeletal muscle

Question 13

How is a steady Vm reached in terms of Na+ and K+ movement

Answer 13

When Na⁺ influx is equal and opposite to efflux of K⁺, no net movement of electrical charge occurs, steady Vm reached

Question 14

How does a plasma membrane’s permeability to Na+ affect its voltage

Answer 14

The greater the Na+ permeability, the more positive Vm becomes

Question 15

Which ions have equilibrium with Vm = -90 mV

Answer 15

K+ and Cl- as their Nernst Potentials are -90mV

Question 16

Are sensory neurons affected by external K+ concentration and are they nernstian

Answer 16

Increases in external K+ concentrations do increase the membrane potential of sensory neurons but they are non Nernstian as the relationship is not logarithmically linear

Question 17

How is the Na+ and K+ concentration gradient and diffusion potential maintained even though they both move towards the concentration gradient

Answer 17

Na+-K+ATPase (Sodium Potassium Pump)

Question 18

Discuss the transfer of K+ ions across a membrane when the intracellular voltage is negative

Answer 18