Question

Bio 474 PSQ 1 & 2

Question 1: Why are the extracellular concentrations of ions surrounding cells in animals about same for each and having the values as shown ( in mM):

[Na+ ]0 = 350 ; [K+ ]0 = 10 ; [Cl- ]0 = 350 ; [Mg++]0 = 50 ; [Ca++]0 = 10

Question 2: Why do inside ion concentrations differ from outside? ( Specifically, why are [Na+ ]0 and [Ca++]0 largely restricted from the inside, whereas K+ is concentrated on the inside of all cells found on planet Earth?)

Answer 1

1. The extracellular concentration of ions in surrounding cells in animals about same because to maintain resting membrane potential across the body in animals (humans).

For a cell’s membrane potential, the reference point is the outside of the cell. In most resting neurons, the potential difference across the membrane is about 30 to 90 mV with the inside of the cell more negative than the outside. That is, neurons have a resting membrane potential (or simply, resting potential) of about -30 to -90mV.

Because there is a potential difference across the cell membrane, the membrane is said to be polarized.

• If the membrane potential becomes more positive than it is at the resting potential, the membrane is said to be depolarized.

• If the membrane potential becomes more negative than it is at the resting potential, the membrane is said to be hyperpolarized.

2. There are several channels across a cell membrane in animals that controlls the gradient of the ions across the cells. This helps to maintain equilibrium or the resting membrane potential.

For sodium there is Na+ - K+ ATPase pump which pumps in out sodium and potassium. Also calcium leaky channels and ATP controlled Ca+ channels are present to controll RMP. Ca+ channels present mainly in heart muscles to maintain potential.