Decaimento do Potencial de Repouso

The resting membrane potential of negative 70 millivolts is maintained by differences in ionic composition and selective permeability across the neuronal membrane. Potassium ions move out through potassium leak channels, making the cell interior negative, while sodium ions slowly enter through sodium leak channels. The sodium-potassium pump continuously moves three sodium ions out and two potassium ions in, counteracting constant ionic leakage and preserving the electrochemical gradient necessary for cell viability.

If the sodium-potassium pump fails or is inhibited for more than 10 seconds, leak channels continue moving ions until equilibrium is reached with no net ion movement. The membrane potential decays to zero as the ionic gradient dissipates. Without the maintained gradient, the cell rapidly loses viability and cannot sustain normal function, making the pump essential for neuronal survival despite not directly generating the resting potential.

Potassium ions are highly permeable and flow outward through leak channels, creating the negative interior charge. Sodium ions move inward more slowly through their leak channels, slightly offsetting potassium's negative effect. The cell's negative interior results from much greater potassium efflux than sodium influx. This selective ion permeability, combined with concentration gradients, establishes the characteristic negative 70 millivolt resting potential.

A neuron resembles a leaky boat because ions constantly move in and out through leak channels despite the cell's efforts to maintain them. The sodium-potassium pump must continuously work to counteract this constant ionic leakage and prevent the loss of concentration gradients. Without active pumping to replace lost ions, the membrane potential would decay, and the cell would lose its ability to function, similar to how a boat would sink without bailing out water.

Although chloride ions do not significantly contribute to establishing the resting membrane potential, their permeability across the membrane is functionally important. Chloride ion movement prevents abrupt, destabilizing changes in membrane potential by providing a buffering effect. This selective permeability helps stabilize the neuronal membrane and supports the role of ion channels in neuronal computation by maintaining controlled electrical conditions.

Potassium efflux stops when the membrane potential reaches a value where the electrical driving force on potassium ions balances the effect of the concentration gradient. At this equilibrium point, no further net movement of ions occurs. The balance between electrical and chemical forces creates a stable resting potential, allowing the cell to maintain its negative interior charge and remain ready to generate signals like action potentials.

The resting membrane potential is crucial because changes in membrane potential, such as action potentials, form the basis for neuronal signaling and communication. A stable resting potential of negative 70 millivolts provides the electrical foundation neurons need to generate and propagate signals. If the resting potential decays to zero due to pump failure, the cell loses its ability to conduct signals, disrupting nervous system function and causing rapid loss of cellular viability.