Question

1. If the membrane potential of sodium ions in a cell is equal to +60 mV, what is its membrane potential for chloride ions if they are found in the exact same concentrations as sodium? Give your answer in mV.

2.

Given a cell membrane with the following parameters-

Ion	Extracellular concentration (mmol/L)	Intracellular concentration (mmol/L)	Permeability
K+	10	150	1
Na+	140	15	0.04
Cl-	100	7	0.45

calculate the membrane potential of the cell in mV. (Round your answer to the nearest hundredth.) Assume standard temperature and pressure.

Answer 1

When we take two electrodes and place one on the outside and the other on the inside of the plasma membrane of a living cell. we can measure an electrical potential difference, or voltage, between the electrodes. This electrical potential difference is called the membrane potential.This potential difference is measured relative to a reference point. 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 we can say have a resting potential) of about −30 mV to −90 mV. Here we can say there is potential difference across the cell membrane, the membrane is polarised. The membrane potential can become either more positive or more negative than that at its resting potential. If it becomes more positive, it is said to be Depolarized and if more negative, its is called Hyperpolarized. These electrical signals are carried by neurons. The most abundant ions in the neurons include positively charged cations that include Na and K and negatively charged anions (Cl and other organic ions)

In most neurons, positively charged Potassium ions and organic anions are present at higher concentrations inside the cell than outside. In contrast, Na+ and Cl− are usually present at higher concentrations outside the cell. This means there are stable concentration gradients across the membrane for all of the most abundant ion types. As the ions are charged, they cannot pass directly through the hydrophobic lipid regions of the membrane. There must be some specialized channel proteins that provide a hydrophilic tunnel across the membrane. Some channels, known as leak channels, are open in resting neurons. Others are closed in resting neurons and only open in response to a signal. Some ion channels are highly selective for one type of ion, but others let various kinds of ions pass through. Ion channels that mainly allow K+ to pass are called potassium channels, and ion channels that mainly allow Na+ to pass are called sodium channel.

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