33.During the propagation of a nerve impulse, action potential results from the movement of A. Na+ ions from extracellular fluid to intracellular fluid B. K+ ions from extracellular fluid to intracellular fluid C. Na+ ions from intracellular fluid to extracellular fluid D. K+ ions from intracellular fluid to extracellular fluid
Option A. The action potential is generated quickly when the negative ions are changed into the positive ions. The movement of the sodium ions into the cell and the movement of potassium ions outside the cell lead to the generation of the nerve impulse. This change takes place in milliseconds. The channels present in the membrane are first to open in order to let in the sodium ions. This starts the nerve impulse. This stage is called the depolarization of the membrane. Then the channels are open in order to move out the potassium ions this leads to the end of the nerve impulse. The inside of the membrane becomes negative again and this stage is known as the repolarization state.After the channels are closed the resting potential is restored and the nerve moves on to the next neuron in the form of a wave. In the presence of the myelinated sheaths on the surface of the neurons, the nerve signals jump from one node to the other. But in the non-myelinated sheath, the flow of nerve impulse is smooth. So, the answer is ‘Na+ ions from extracellular fluid to intracellular fluid’.
