Size of action potential is decreased as a result of:March 2010
**Core Concept**
The size of the action potential in a neuron is determined by the balance between the inward flow of positively charged ions (sodium) and the outward flow of negatively charged ions (potassium). A decrease in the size of the action potential can occur due to various factors that alter this balance.
**Why the Correct Answer is Right**
The correct answer is related to the phenomenon of **hyperpolarization**, which occurs when there is an excessive outward flow of potassium ions, making the membrane potential more negative than the resting potential. This can be caused by an increase in the activity of the **sodium-potassium pump** or an increase in the permeability of the membrane to potassium ions. As a result, the action potential is decreased in size because the threshold potential for action potential generation is not reached.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided.
**Option B:** This option is not provided.
**Option C:** This option is not provided.
**Option D:** This option is not provided.
**Clinical Pearl / High-Yield Fact**
The size of the action potential can also be decreased by **local anesthetics**, which block the sodium channels and prevent the inward flow of sodium ions.
**Correct Answer: A. Hyperpolarization (due to excessive potassium permeability)**