Explain the following questions. I am wanting to understand this better. 1. Expl

Question

Explain the following questions. I am wanting to understand this better.

1. Explain the theory behind the Nernst Potential, i.e., using the basic laws.
2. What are the approximate Nernst potentials for K+, Na+, and Cl- in a neuronal cell?
What do they depend on?
3. Write the equation for calculating the Nernst potential.
4. What will decreasing the internal concentration of K+ do to its Nernst potential?
5. How do the individual Nernst potentials determine the resting membrane potential?
6. What is the GHK equation?
7. If the permeability to Na+ is increased, how would this affect its Nernst potential?
8. If the permeability to Na+ was increased, how about the resting potential of the cell?
9. Of the major ions contributing to the resting membrane potential, which is the one
that has a larger intracellular concentration compared to its concentration outside?
10. If the external concentration of Na+ is increased, what will happen to the resting
potential of the cell? What if the external concentration of K+ is increased?

Thank you!

Explanation / Answer

1. Nernst potential is also known as reverse potential (for biological membranes) of an ion at which there is no net flow of the ion from one side of the membrane to the opposite side. In case of neurons, Nernst potential is the membrane potential at which a given neurotransmitter causes no net current flow (of ions) through that neurotransmitter's receptor's ion channel.

2. Approximate Nernst potentials for K+, Na+, Cl- in a neuronal cell are -90mV, +55mV, and -65mV respectively

3. Equation for calculating Nernst potential is

Veq= equilibrium or Nernst potential

R is the universal Gas constant

T is the temperature in K

Z is the valence of the ionic species

F is the Faraday's constant

(X)out is the concentration of ionic species X in the extracellular fluid

(X)in is the concentratio of the ionic species X in the intracellular fluid, typically expressed in milli Moles

4. Decreasing the K+ concentration inside the cell leads to an increase in the Nernst potential to a positive value. For example, if the K+ ion concentration in cells is 10 times less than the same external to the cell, the Nernst potential reaches +58 mV.

5. The individual Nernst potential results from teh movement of the ions across the membrane. Resting membrane potential is due to the unequal distribution of ions on both sides of the membrane. Owing to the difference in the ions across the membrane, it generates a voltage or potential.

6. The Goldman-Hodgkin-Katz flux equation is used to describe the inoic flux across a cell membrane as a function of the transmembrane potential and the concentrations of the ion inside and outside of the cell. The equation is generally used in cell membrane physiology to determine the Nernst potential across a cell membrane.

7. If permeability of sodium ions is increased, the Nernst potential would approach a value of +55 mV, if there is no change in the permeabilit of K+ ions. On the other hand, if Na+ and K+ are equally permeable, the Nernst potential reaches a value of 0 mV.

8. Equilibrium potential remain unchages. Changing permeability does not change the equilibrium potential.

9. K+ ions have a greater intracellula concentration compared to their extracellular concentration.

10. Increasing the external K= concentration leads to depolarization in the resting potential of the membrane.

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