Total sum of physio-electrochemical changes that takes place along the length of nerve fibre is known as nerve impulse. Change in potential due to stimulation of nerve fibre is called action potential. During propagation of nerve impulse, Na⁺ enters inside so(+ve) change is formed inside the membrane. K⁺ ions come out.

Propagation of a Nerve Impulse and the Action Potential

When a nerve impulse is propagated along a neuron, it involves a series of events that result in the generation and transmission of an electrical signal. This process is crucial for communication between neurons and the transmission of information throughout the nervous system.

Action Potential and Ion Movement

The action potential refers to the rapid change in electrical potential that occurs when a neuron is stimulated. It is generated by the movement of ions across the cell membrane, specifically sodium (Na+) and potassium (K+) ions. These ions play a vital role in creating and propagating the action potential.

Ion Movement during an Action Potential

During the resting state of a neuron, the intracellular fluid has a higher concentration of potassium ions (K+) compared to the extracellular fluid, while the extracellular fluid has a higher concentration of sodium ions (Na+). This difference in ion concentrations creates an electrical gradient across the cell membrane.

When a neuron is stimulated, such as by a neurotransmitter binding to its receptors, the permeability of the cell membrane changes, allowing ions to move across the membrane. This change in permeability leads to the movement of Na+ ions from the extracellular fluid to the intracellular fluid.

Depolarization and Sodium Ion Movement

Depolarization is the first phase of the action potential. It occurs when the membrane potential becomes less negative, moving towards a positive value. During depolarization, the sodium channels on the cell membrane open, allowing sodium ions (Na+) to move from the extracellular fluid into the intracellular fluid. This influx of positive ions further depolarizes the membrane.

Repolarization and Potassium Ion Movement

Repolarization is the second phase of the action potential. It occurs when the membrane potential returns to its resting state after depolarization. During repolarization, the potassium channels on the cell membrane open, allowing potassium ions (K+) to move from the intracellular fluid to the extracellular fluid. This movement of positive ions out of the cell helps restore the negative charge inside the cell, leading to repolarization.

Hyperpolarization and Ion Redistribution

After repolarization, a brief period of hyperpolarization may occur. During this phase, the cell membrane becomes more negative than its resting state. This is due to the continued efflux of potassium ions (K+) and slower closure of potassium channels. Eventually, the ion concentrations return to their resting levels through the activity of ion pumps, which actively transport sodium and potassium ions across the cell membrane.

Conclusion

In conclusion, the action potential during the propagation of a nerve impulse results from the movement of sodium (Na+) ions from the extracellular fluid to the intracellular fluid. This movement of ions is responsible for the depolarization phase of the action potential. The subsequent repolarization phase is driven by the movement of potassium (K+) ions from the intracellular fluid to the extracellular fluid. Overall, the coordinated movement of these ions is essential for the generation and transmission of electrical signals in neurons.

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