**Question:** Resting membrane potential is mainly due to -

A. Depolarization
B. Hyperpolarization
C. Calcium ions
D. Sodium and Potassium channels

**Core Concept:**
Resting membrane potential is a crucial component of a neuron's electrical properties, primarily determined by the balance of ions, specifically sodium (Na+) and potassium (K+) ions, across the neuron membrane. A neuron's resting membrane potential is necessary for proper communication within the nervous system and serves as the foundation for various physiological processes, including action potentials and signal transmission.

**Why the Correct Answer is Right:**
The correct answer, D, highlights the role of sodium and potassium channels in maintaining the resting membrane potential. These channels are responsible for the selective permeability of the cell membrane to these ions. Sodium channels allow the influx of Na+ ions when open, causing depolarization. Potassium channels, on the other hand, allow K+ ions to exit the cell, hyperpolarizing it. The balance between these two processes results in the resting membrane potential.

**Why Each Wrong Option is Incorrect:**
A (Depolarization) is incorrect because it refers to an increase in membrane potential, which occurs during action potentials, not the resting membrane potential.
B (Hyperpolarization) is incorrect because it refers to a decrease in membrane potential, the opposite of the resting membrane potential.
C (Calcium ions) is incorrect because calcium ions play a role in neurotransmitter release and muscle contraction but are not directly responsible for the resting membrane potential.

**Clinical Pearl:**
Understanding the resting membrane potential is essential for understanding neuronal function and communication in the nervous system. Any disruption in the balance of sodium and potassium channels can lead to various neurological conditions, such as epilepsy, where abnormal depolarization occurs due to excessive sodium influx or potassium efflux.