Question

The charge on the outer side of neuron in resting phase is

• A. positive
• B. negative
• C. zero
• D. alternate -ve and +ve

Answer 1

The correct option is A positive

When there is no stimulus given to the neuron, the potential difference across its plasma membrane is called resting membrane potential. This phase is called the polarised state of the neuron.

During this phase, the sodium-potassium pump moves $3N{a}^{+}$ ions out of the cell for every $2K^{+}$ ions it moves into the cell. As a result, the concentration of sodium ions is more outside the membrane than the inside. Whereas the concentration of $K^{+}$ ions is more on the inside of the cell than on the outside of the cell. Also the membrane is impermeable to the sodium ions. Due to the difference in concentration of $K^{+}$ ions, a potassium ion concentration gradient is created. As a result, the $K^{+}$ ions will diffuse from the inside of the cell to outside of the cell via $K^{+}$ channels. As the potassium ions leave the cell, it increases negative charges on the inside of the cell and the positive charges are accumulated outside of the cell. Also the membrane is impermeable to the negatively charged proteins on the inside of the cell. Due to this the inside of the cell is comparatively negative to the outside. Whereas the positive charge gets accumulated outside the axonal membrane of the neuron in the resting phase.