Question

A medication that increases the amount of Na+ in the extracellular fluid surrounding a neuron will do which of the following to that neuron?

Depolarize

Hyperpolarize

Activate

Have no effect.

Answer 1

Answer) Hyperpolarize

Explanation - The resting membrane potential is negative inside and positive outside the membrane of the nerve.

The negative resting membrane potential present inside the nerve is due to distribution of ions across the cell membrane. More potassium ions diffuses out of the cell (relative to entry of sodium ions into the cell), while non-diffusable anions (eg. Proteins) stay in the cell.

Therefore, there is slight excess of positive ions outside the membrane of nerve and slight excess of negative ions inside the nerve causing negative resting membrane potential inside the nerve. It ranges from the - 40 to - 90mV. The minus sign indicates that the inside of the cell is negative relative to the outside.

The membrane potential can change from its resting value when the membrane's permeability to particular ions changes.

If the inner side becomes less negative, it is said to be depolarization. If the inner side becomes more negative, it is said to be hyperpolarized.

If the Sodium (Na+) ions is present more in amount in the extracellular fluid (outside the membrane of the nerve), then there will be more positive ions outside the nerve and more negative ions build up inside the nerve. So the inner side becomes more negative causing Hyperpolarizarion.

Therefore, the medication which increases the amount of sodium ions in extracellular fliud will cause Hyperpolarizarion of nerve.

Other options are incorrect-

-Depolarize is incorrect as depolarization occurs when inside of the nerve becomes less negative.

As the sodium ions present more amount in the extracellular fliud than inside the nerve. Then there will be more negative ions inside causing Hyperpolarization(not depolarization).

Depolarization occurs when the sodium ions present in more amount inside the cell (not in extracellular fliud).

-activate is incorrect as activation of neuron occurs when there is production of action potential in the neuron.

An action potential occurs when depolarization reaches a certain leve called threshold potential (-55 mV).

The threshold potential occurs when there is more amount of sodium ions inside the nerve (not in the extracellular fluid).

-Have no effect is incorrect as there is hyperpolarislzation of the neuron.