Question

During resting potential, the axonal membrane is polarised, indicate the movement of +ve and –ve ions leading to polarisation diagrammatically.

Answer 1

Cause :

The resting membrane potential exists because of a small buildup of negative ions in the cytosol along the inside of the membrane and an equal buildup of positive ions in the extracellular fluid along the outside surface of the membrane. It arises due to unequal distribution of ions mainly $N{a}^{+}$ and $K^{+}$ in the extracellular fluid and cytosol.

Mechanism :

Resting membrane potential arises due to

• Permeability of the plasma membrane of the axon- The plasma membrane is more permeable to $K^{+}$ ion than $N{a}^{+}$ ion as the membrane has more potassium ions leakage channels than sodium leakage channels. More $K^{+}$ ions move outside the membrane as compared to the inward transport of $N{a}^{+}$ ions. As more $K^{+}$ ions exit, the charge inside the membrane becomes more negative than the extracellular fluid.
• The anions cannot follow the $K^{+}$out of the cell because they are attached to non-diffusible molecules such as ATP and large proteins.
• Sodium potassium pump helps in maintaining the resting membrane potential by exporting three $N{a}^{+}$ ions and importing two $K^{+}$ ion. These pumps move more positive charge from the cell than they bring into the cell, so they contribute to the negative charge of the resting membrane potential.
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