Question

Action potential results from the movement of

• A. ${\mathrm{Na}}^{+}$ from intracellular fluid to extracellular fluid
  
• B. ${\mathrm{Na}}^{+}$ from extracellular fluid to intracellular fluid
• C. ${\mathrm{Na}}^{+}$ in both directions
• D. Stagnation of ${\mathrm{Na}}^{+}$ ions

Answer 1

The correct option is B ${\mathrm{Na}}^{+}$ from extracellular fluid to intracellular fluid

In the human body, the intracellular fluid has higher $K^{+}$ ions than ${\mathrm{Na}}^{+}$ ions. Whereas outside the cell, the ${\mathrm{Na}}^{+}$ ion concentration is higher than $K^{+}$ ion.

In case of a neuron, there are ion leakage channels. But there are more $K^{+}$ ion leakage channels than ${\mathrm{Na}}^{+}$ ion leakage channel. As $K^{+}$ ion is higher inside and lower outside the cell, it starts moving out of the cell along the concentration gradient.

Due to further movement of ions, the membrane facing the cytoplasm is more electronegative than the extracellular fluid.

When the neuron is stimulated by the binding of neurotranmitter on the ligand gated ${\mathrm{Na}}^{+}$ ion channel, the charge in the neuron is reversed due to entry of ${\mathrm{Na}}^{+}$ ions from the extracellular fluid into the cell along the concentration gradient.

This results in the reversal of charges across the neuron membrane. The inside of the membrane becomes positive compared with the outside of the membrane. This is called the action potential.

Hence, action potential results from the movement of ${\mathrm{Na}}^{+}$ from the extracellular fluid to intracellular fluid.