Resting Membrane Potential

RESTING MEMBRANE POTENTIAL

Q. 1

The resting membrane potential of a cell:

 A

Is dependent on the permeability of the cell membrane to K+ being greater to Na+

 B

Falls to zero if Na+/K+ ATPase in membrane is inhibited

 C

Is equal to the equilibrium potential for K+

 D

Is equal to the equilibrium potential of Na+

Q. 1

The resting membrane potential of a cell:

 A

Is dependent on the permeability of the cell membrane to K+ being greater to Na+

 B

Falls to zero if Na+/K+ ATPase in membrane is inhibited

 C

Is equal to the equilibrium potential for K+

 D

Is equal to the equilibrium potential of Na+

Ans. A

Explanation:

Is dependent on the permeability of the cell membrane to K+ being greater to Na+ REF: Ganong, 22nd edition, BRS physiology, 4th edition page 11

Ionic Basis of nerve Resting Membrane Potential:

  • Resting membrane potential is potential difference across the cell membrane in millivolts. Which is by convention -70 Mv
  • Resting membrane potential is established by diffusion potential that results from concentration differences of permeable ions. And each permeable ion attempts to derive the membrane potential towards its equilibrium potential.
  • Resting membrane potential (-70 mV) is close to equilibrium potential of K+ and C1– (both -85 mV) and far away from the equilibrium potential of Na+ ( +65 mV). That means at rest the nerve membrane is more permeable to K+ than Na+
  • Na+ is actively transported out of neurons and other cells and K+ is actively transported into cells, but because of K+ permeability at rest is greater than Na+ permeability. Therefore, K+ channels maintain the resting membrane potential.

Ionic Basis of nerve Action Potential:

  • Depolarization causes rapid opening of the activation gates of Na+ channels and thus Na+ conductance promptly increases. Thus the membrane potential is driven towards the equilibrium potential of Na+ ion (+65 mV)
  • Thus the rapid depolarization during upstroke is due to inward Na+ current
  • Depolarization slowly opens K+ channels and increases K+ conductance to even higher levels than at rest.
  • The combined effect of closing Na+ channels and greater opening of K+ channels make the K+ conductance higher than the Na+ conductance and membrane potential is repolarized. Thus repolarization is caused by outward K+ current.
  • The K+ conductance remains higher than at rest for some time after closure of Na+ channel and the membrane potential is driven more closer to K+ equilibrium potential than at rest. This is called as undershoot.

Q. 2 Which of the following would cause an immediate reduction in the amount of potassium leaking out of a cell?
 A Increasing the  permeability of  the  membrane to potassium
 
 B Increasing (hyperpolarizing) the membrane otential 
 C Decreasing the extracellular potassium concentration
 D Reducing the activity of the sodium-potassium pump
Q. 2 Which of the following would cause an immediate reduction in the amount of potassium leaking out of a cell?
 A Increasing the  permeability of  the  membrane to potassium
 
 B Increasing (hyperpolarizing) the membrane otential 
 C Decreasing the extracellular potassium concentration
 D Reducing the activity of the sodium-potassium pump
Ans. B

Explanation:

The amount of potassium leaking out of the cell depends on its driving forces and its membrane conductance. The driving forces are the membrane potential and the concentration gradient. Hyperpolarizing the membrane makes the inside of the cell more negative and therefore, makes it more difficult for potassium to flow out of the cell. Increasing the permeability of the membrane to potassium or decreasing the extracellular potassium concentration increases the flow of potassium out of the cell. Altering the activity of the

sodium-potassium pump or the extracellular sodium concentration has no immediate effect on the flow of potassium

across the membrane. However, decreasing the activity of the sodium-potassium pump will ultimately depolarize the membrane, increasing the flow of potassium out of the cell.


Q. 3

Equilibrium potential for an ion is calculated using

 A

Gibbs Donnan equation

 B

Goldman equation

 C

Nernst equation

 D

Henderson Hesselbach equation

Q. 3

Equilibrium potential for an ion is calculated using

 A

Gibbs Donnan equation

 B

Goldman equation

 C

Nernst equation

 D

Henderson Hesselbach equation

Ans. C

Explanation:

Nernst Equation [Ref: Ganong 22/c p6,7; various websites]

  • Equilibrium potential: The electrochemical potential difference across a semi-penneable membrane, when a diffusible ion is at equilibrium is called the equilibrium potential. It can be calculated using Nernst equation.
  • Explanation of Nernst equation or Nernst Equilibrium
  • Consider the following 2 compartment system:
  • Both compartments contain KC1, but compartment 1 is at a higher concentration. If the membrane allowed KC1 to cross, KCI, its constituent ions le and                                 ions, would diffuse from compartment 1 to compartment 2.
  • Suppose the membrane is penneable only to K4 ions. K+ will tend to diffuse from compartment I to compartment 2. but ions cannot because the membrane is not permeable to them. As soon as this happens there will be a net transfer of positive charge from compartment 1 to 2 (carried by the K4 ions) and compartment 2 will become electrically positive with respect to compartment 1.
  • Now the electrical gradient will tend to push K” ions from compartment 2 to compartment 1. Very quickly, equilibrium will be established in which the electrical difference will be just large enough to move IC’ ions to the left at the same rate as they tend to diffuse to the right due to the concentration gradient. The electrical potential difference at which this happens is called the Nernst potential or equilibrium potential.
  • The Equilibrium Potential is calculated by the Nernst Equation

RT        fXI,, E, = —zxF IX);

where

  • E., is the Nernst potential for ion X (measured as. for membrane potentials – inside with respect to outside)
  • [XL, is the concentration of X outside the cell
  • [X]i is the concentration of X inside the cell
  • zx is the valence of ion X
  • R is the gas constant
  • T is the absolute temperature
  • F is Faraday’s constant
  • The Nernst equilibrium potential for an ion (usually referred to as either the Nernst potential or the equilibrium potential) is thus the potential across the membrane that, if it existed, would produce an electrical force on an ion that exactly opposes the force on that ion due to the concentration gradient of the ion.

Gibbs-Donnan Equation

  • The Gibbs-Donnan effect (also known as the Donnan effect, Donnan law, Donnan equilibrium, or Gibbs-Donnan equilibrium) is a name for the behavior of charged particles near a semi-permeable membrane to sometimes fail to distribute evenly across the two sides of the membrane due to the presence of a different charged substance that is unable to pass through the membrane and thus creates an uneven electrical charge.
  • For example, the negative charge of a nondiffusible anion hinders diffusion of the diffusible cations and favors diffusion of the diffusible anions.
  • Suppose: two compartments A and B are separated by a semipermeable membrane. Both sides contain K+ and Cl­ions permeable through the membrane. Side A contains nondiffusible protein anions.
  • The diffusible ions will distribute themselves across the membrane in such a manner that at equilibrium, their concentration ratios are equal i.e.

Thus:

The product of concentration of a pair of diffusible cations and anions on one side of the semipermeable membrane will equal the product of the same pair of ions on the other side.

This is the Gibbs-Donnan equation.

  • The gibbs-donnan equation holds true for any univalent anion cation pair in equilibrium between two chambers.
  • A system in Gibbs-Donnan equilibrium has a number of important features at equilibrium:

– The compartment containing the impermeant ion contains more osmotically active ions. (thus because of anionic proteins in the cells, there are more osmotically active particles in cells than in the interstial fluid. Osmosis would thus make them swell and eventually rupture if it were not for Na+-K+ ATPase pump pumping ions back out of the cells.)

– Because at equilibrium the distribution of permeant ions across the membrane is asymmetric, an electrical difference exists across the membrane whose magnitude can be determined by the Nersnt equation. The compartment containing the impermeant anion has a negative potential.

The Goldman-Hodgkin-Katz voltage equation, more commonly known as the Goldman equation is used in cell membrane physiology to determine the potential across a cell’s membrane taking into account all of the ions that are permeant through that membrane.

The Henderson-Hasselbalch equation describes the derivation of pH as a measure of acidity (using pKa, the acid dissociation constant) in biological and chemical systems. The equation is also useful for estimating the pH of a buffer solution and finding the equilibrium pH in acid-base reactions (it is widely used to calculate isoelectric point of the proteins).


Q. 4

Equilibrium potential for an ion is calculated using?

 A

Gibbs Donnan equation

 B

Goldman–Hodgkin–Katz voltage equation

 C

Nernst equation

 D

Henderson Hasselbach equation

Q. 4

Equilibrium potential for an ion is calculated using?

 A

Gibbs Donnan equation

 B

Goldman–Hodgkin–Katz voltage equation

 C

Nernst equation

 D

Henderson Hasselbach equation

Ans. C

Explanation:

Chloride ions (Cl–) are present in higher concentration in the ECF than in the cell interior, and they tend to diffuse along this concentration gradient into the cell. The interior of the cell is negative relative to the exterior, and chloride ions are pushed out of the cell along this electrical gradient. An equilibrium is reached between Cl– influx and Cl– efflux. The membrane potential at which this equilibrium exists is the equilibrium potential. Its magnitude can be calculated from the Nernst equation, as follows:

where

ECl = equilibrium potential for Cl–
 
R = gas constant
 
T = absolute temperature
 
F = the Faraday number (number of coulombs per mole of charge)
 
ZCl = valence of Cl– (–1)
 
[Clo–] = Cl– concentration outside the cell
 
[Cli–] = Cl– concentration inside the cell
 
Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 1. General Principles & Energy Production in Medical Physiology. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.

Q. 5

Resting membrane potential of nerve is equal to equilibrium potential of

 A

Na+

 B

Cl-

 C

K+

 D

HCO3-

Q. 5

Resting membrane potential of nerve is equal to equilibrium potential of

 A

Na+

 B

Cl-

 C

K+

 D

HCO3-

Ans. B

Explanation:

B i.e. Chloride ion


Q. 6

Resting membrane potential in nerve fibre

 A

Is equal to the potential of ventricular muscle fibre

 B

Can be measured by surface electrodes

 C

Increases as extra cellular K+ increases

 D

Depends upon K+ equilibrium

Q. 6

Resting membrane potential in nerve fibre

 A

Is equal to the potential of ventricular muscle fibre

 B

Can be measured by surface electrodes

 C

Increases as extra cellular K+ increases

 D

Depends upon K+ equilibrium

Ans. D

Explanation:

D i.e. Depends on potassium ion equilibrium


Q. 7

Equilibrium potential for an ion is calculated using:

 A

Gibbs-Donnan equation

 B

Nerst equation

 C

Goldman equation

 D

None

Q. 7

Equilibrium potential for an ion is calculated using:

 A

Gibbs-Donnan equation

 B

Nerst equation

 C

Goldman equation

 D

None

Ans. B

Explanation:

B i.e. Nernst equation

Equilibrium potential (i.e., membrane potential at which equilibrium b/w concentration & electrical gradient exist) for any (one) univalent ion is calculated by Nernst equationQ and for several different ions by Goldmann- Hodgkin-katz equation.


Q. 8

Which ion helps is resting membrane potential in neurons:             

September 2005, March 2013

 A

Potassium

 B

Calcium

 C

Chloride

 D

Sodium

Q. 8

Which ion helps is resting membrane potential in neurons:             

September 2005, March 2013

 A

Potassium

 B

Calcium

 C

Chloride

 D

Sodium

Ans. A

Explanation:

Ans. A: Potassium

In neurons resting membrane potential is about -70 mV, which is close to the equilibrium potential of potassium ions


Q. 9

Electric potential of resting membrane for a given electrolyte is given by which equation ‑

 A

Nernst

 B

Goldman

 C

Donnan-Gibbs

 D

None

Q. 9

Electric potential of resting membrane for a given electrolyte is given by which equation ‑

 A

Nernst

 B

Goldman

 C

Donnan-Gibbs

 D

None

Ans. A

Explanation:

Ans. is ‘a’ i.e., Nernst


Q. 10

Resting membrane potential in cardiac muscle ‑

 A

-70 mV

 B

+70 mV

 C

-90 mV

 D

+90 mV

Q. 10

Resting membrane potential in cardiac muscle ‑

 A

-70 mV

 B

+70 mV

 C

-90 mV

 D

+90 mV

Ans. C

Explanation:

Ans. is ‘c’ i.e., -90 mV

Normal RMP in myocardial fibers is about -90 mV.


Q. 11

Maximum equilibrium potential is for –

 A

Na+

 B

K+

 C

Cl

 D

None

Q. 11

Maximum equilibrium potential is for –

 A

Na+

 B

K+

 C

Cl

 D

None

Ans. B

Explanation:

Ans. is ‘b’ i.e., K+


Q. 12

Hair cells baseline membrane potential O‑

 A

30mV

 B

-50mV

 C

-40mV

 D

-60mV

Q. 12

Hair cells baseline membrane potential O‑

 A

30mV

 B

-50mV

 C

-40mV

 D

-60mV

Ans. D

Explanation:

Ans. is ‘d’ i.e., -60mV

The resting membrane potential of the hair cells is about -60 mV.

When the stereocilia are pushed toward the kinocilium, the membrane potential is decreased to about -50 mV.

When the bundle of processes is pushed in the opposite direction, the cell is hyperpolarized.

Displacing the process in a direction perpendicular to this axis provides no change in membrane potenital, and displacing the processes in directions that are intermediate between these two directions produces depolarization or hyperpolarization that is proportional to the degree to which the direction is toward or away from the kinocilium.

Thus, the hair processes provide a mechanism for generating changes in membrane potential proportional to the direction and distance the hair moves.


Q. 13

Equilibrium potential of Cl ions ‑

 A

+ 60 mV

 B

+90 mV

 C

-90 mV

 D

-70 mV

Q. 13

Equilibrium potential of Cl ions ‑

 A

+ 60 mV

 B

+90 mV

 C

-90 mV

 D

-70 mV

Ans. D

Explanation:

Ans. is d i.e., -70 mV



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