Question

Explain the reason that the resting potential for neurons is around -70mV. Be sure to include the roles of the K+ and Na+ concentration gradients, electrical forces, passive ion channels and the relative permeabilities of K+ and Na+. Now, say that an alien race was discovered from a distant galaxy. Their cells have a higher concentration of Na+ inside than outside their cells and a higher concentration of K+ outside than inside. If this race’s neurons otherwise had the same relative permeability to K+ and Na+ at rest that Earth organisms have, what might an approximate value of the resting potential of these alien’s cells be? Why?

Answer 1

There is a stable separation of charges across the cell membrane called the resting potential. There are more positive charges on the outside of the membrane and more negative charge along the inside of the cell. i.e.. anions are dominant inside the cell and cations are predominant outside the cell. Keeping the net charge outside the cell as a reference with 0 mV, it is found that about - 70 milli volt is present inside the membrane. This is a common resting membrane potential for a neuron. Resting membrane potential of neurone is related to concentration differences called gradients of many ions across the cell membrane. The cation that is more important for neuron function are potassium K+ , Sodium Na+, and calcium Ca2+. Most common anions are chloride Cl-, multiple organic anions (most of these are proteins that carry negative charge). Thee organic anions and potassium have a higher concentration inside the neurone than outside.The concentration of sodium is much higher outside the neuron than inside the neurone as the concentration of calcium. There is much more calcium outside the neuron than inside and the concentration of chloride ions is also much higher outside the neurone than inside the neuron. Each of these ions therefore is going to be acted on by two forces that try to drive them into or out of the neuron.
The first is an electrical force from the membrane potential. Because each ions attracted to the side of the membrane with the opposite charge. Opposite charges attract each other and like charges repel each other. Hence negatively charged organic anions and chloride inside the membrane are attracted towards the positively charged side, that is outside the membrane. And positively charged potassium, sodium and calcium are attracted towards inside the membrane.
Second the force acting on the science is diffusion force. It is related to the concentration gradient across the neuron membrane. Because particles in solution will always try to move from an area of higher concentration to an area of lower concentration.
Sodium potassium ATPase pump is involved in the concentration gradient of sodium and potassium across the membrane. It pumps out 3 Na+ outside the the membrane and takes 2 K+ into the The cytoplasm. This create a slight negative charge inside the membrane compared to the outside. It comes around -5 mV. Some K + ions sneaking outside through potassium channels from the cell. It makes the inside potential more negative. This results in ending up of a membrane potential of -70 milli Volt inside the cell.

In the case of alien referred in the question, the situation across the membrane is reversed.But since the permeability is remains same for potassium and sodium ions, there will not be significant change in the the membrane potential. Final membrane potential will remain same. The permeability of Ions are responsible for the membrane potential.