**Question:** Outer membrane action potential is maintained by influx of

A. Calcium ions (Ca2+)
B. Sodium ions (Na+)
C. Potassium ions (K+)
D. Hydrogen ions (H+)

**Core Concept:**
The outer membrane action potential is a short-lived, negative electrical potential that occurs on the outer surface of certain cells, such as neurons and muscle cells during muscle contractions. It is essential for the propagation of action potentials along the cell membrane and the transmission of nerve impulses. The maintenance of this potential is crucial for normal cellular function.

**Why the Correct Answer is Right:**
Outer membrane action potentials are primarily maintained by the influx of positively charged sodium ions (Na+) through voltage-gated sodium channels. These channels open when the membrane potential becomes depolarized, allowing Na+ ions to flow into the cell, causing the membrane to become even more positive, and thus maintaining the depolarization that occurs during the action potential.

**Why Each Wrong Option is Incorrect:**
A. Calcium ions (Ca2+) are involved in various cellular processes, such as muscle contraction and neurotransmitter release. However, they are not directly responsible for maintaining the outer membrane action potential.

B. Sodium ions (Na+) are the primary ions responsible for depolarization during the action potential, but they are not directly involved in maintaining the outer membrane action potential.

C. Potassium ions (K+) are primarily responsible for repolarization during the action potential, preventing the membrane from becoming too positive, but they are not directly involved in maintaining the outer membrane action potential.

D. Hydrogen ions (H+) are not involved in maintaining the outer membrane action potential. They primarily regulate pH balance within the cell and extracellular space.

**Core Concept:**
In neurons, the depolarization of the outer membrane during an action potential is maintained by the influx of positively charged sodium ions (Na+) through voltage-gated sodium channels. These channels open when the membrane potential reaches a certain threshold, allowing Na+ ions to flow into the cell, depolarizing the membrane and maintaining the depolarization occurring during the action potential.

**Why the Correct Answer is Right:**
The correct answer, sodium ions (Na+), are responsible for depolarizing the membrane during an action potential. When the membrane potential reaches a specific threshold, voltage-gated sodium channels open, allowing Na+ ions to flow into the cell, causing the membrane to become more positive, thus maintaining the depolarization that occurs during the action potential.

**Why Each Wrong Option is Incorrect:**
A. Calcium ions (Ca2+) are involved in various cellular processes, such as muscle contraction and neurotransmitter release. However, they are not directly responsible for maintaining the outer membrane action potential.

B. Potassium ions (K+) are primarily responsible for repolarization during an action potential, causing the membrane potential to become more negative after depolarization. They do not directly contribute to maintaining the depolarization that occurs during an action potential.

C. Chloride ions (Cl-) are involved in cell volume regulation and osmoregulation but are not directly involved