Question

discuss the steps involved in forming an action potential, starting with the opening of voltage-gated sodium channels

Answer 1

Ans. A nerve cell has separate ionization potential on both the intracellular fluid and extracellular fluid. This difference in potential is maintained by different concentrations of ions on the inside and outside of cell. The ions that have main contributions in creating this potential difference are sodium ions, potassium ions, chloride ions and bicarbonate ions. In the normal resting condition, there are more number of negative ions in the interior of the cell than the exterior. This action is accomplished by the sodium-potassium pump which extrudes 3 sodium ions outside the cells, while pumps 2 potassium ions inside the cell. This creates a concentration gradient of sodium ions with more number of sodium ions outside the cell than inside.

As a nerve receives stimulation, voltage gated sodium ion channels open. Due to high concentration difference of sodium ions between inside and outside the cell, sodium ions rapidly rush into the cell creating positive membrane potential within the cell compared to the outside. This condition is called depolarization. This shooting up of the membrane potential within the nerve cell upon stimulation is called action potential.

As the stimulation moves forward down the nerve cell towards the synaptic end, the front portion gets depolarized while the previous portion gets repolarized. Repolarization occurs by gradual inactivation of voltage gated sodium ion channels. Along with this, potassium leak channels also allow the exit of potassium ions out of the cell. This causes further fall in membrane potential within the nerve cell. This condition is called hyperpolarized state. During this stage, next stimulus is unable to excite the nerve cells again. After this stage, the nerve cell again returns back to its normal polarized state.