MEDICAL PHYSIOLOGY

Detailed explanation-1: -In neurons, the rapid rise in potential, depolarization, is an all-or-nothing event that is initiated by the opening of sodium ion channels within the plasma membrane. The subsequent return to resting potential, repolarization, is mediated by the opening of potassium ion channels.

Detailed explanation-2: -A stimulus first causes sodium channels to open. Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Remember, sodium has a positive charge, so the neuron becomes more positive and becomes depolarized.

Detailed explanation-3: -In the open state, voltage-gated sodium channels form a pore in the cytoplasmic membrane that allows sodium ions to flow into the cell, depolarizing the cell and generating the upstroke of the action potential; however, most sodium channels rapidly transit into the “inactivated” state at depolarized potentials.

Detailed explanation-4: -The rapid depolarization or the upstroke of the neuronal action potential occurs as a result of the opening of the voltage-gated sodium channels.

Detailed explanation-5: -Depolarization is caused when positively charged sodium ions rush into a neuron with the opening of voltage-gated sodium channels. Repolarization is caused by the closing of sodium ion channels and the opening of potassium ion channels.