When a neuron is polarized, O a) both positive and negative ions are concentrated inside the neural membrane b) positive ions are concentrated outside the neural membrane while negative ions are concentrated inside the membrane c) negative ions are concentrated outside the neural membrane while positive ions are concentrated inside the membrane d) both positive and negative ions are concentrated outside the neural membrane

The word polarized means that there is a charge difference which is responsible for the occurrence of the potential difference across the membrane. Usually the charge is because of the positively charged cations and negatively charged ions anions. B. Positive ions are concentrated outside the neural membrane while negative ions are concentrated inside the membrane. Explanation- Explanation- it has been estimated that the sodium ions are about 14 times more in the ECF than in the cytosol. Obviously these ions tend to move downhill their concentration gradient from ECF into the cytosol. Since however the sodium ion channels of Plasma membrane normally remains closed, the membrane is very slightly permeable to these ions. Consequently a large number of Na+ ions accumulate at the outer surface of the plasma membrane. This build up of Na+ attracts the anions that is proteins and organic phosphets of cytosol. The plasma membrane is impermeable yo these anions. Hence there anions accumulate at the inner surface of the plasma membrane. The electric voltage difference across the plasma membrane due to the build up of cations on the outer side and of the anions on the inner side is a form of potential energy. it is call membrane potential. It averages minus 70 mv on inside of the plasma membrane in respect to outside of the membrane. Because of the potential the cells are said to be polarized. Second factor which is responsible for the maintenance of this polarized state is Sodium Potassium pump which are located on the membrane. The inward leakage of Na+ and outward leakage of k+ disturb the electrochemical gradient of the membrane potential. For this three sodium ions move from inside to outside and in its exchange two potassium ions moves from outside to inside, again maintaining the polarised state of the neural membrane. This is a sort of active transport thus it uses energy from ATP hydrolysis.Explanation for wrong answers- Option a is incorrect as both the negative and positive charges are not accumulated inside the membrane. if it would have been the case then both negative and positive charges would have neutralized each other and there would have been no charge on the membrane which is not the case. option c is incorrect because if negative charges would have been concentrated outside the membrane then outside would have been negatively charged in comparison to inside which is not the case. Last option is incorrect because if both negative and positive charges equally would have been concentrated outside the membrane then the outside membrane would have been neutral which is not the case.

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