Question

The neurons may get irreversibly damaged if exposed to significant hypoxia for

• A. 8 minutes
• B. 2 minutes
• C. 30 seconds
• D. 15 seconds

Hint:

Standard teaching puts irreversible neuron damage at about 4 to 6 minutes of complete anoxia; this paper's key is self flagged as uncertain.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks how long neurons can be starved of oxygen (hypoxia) before the damage becomes permanent, not just temporary and reversible.

Step 2: Key Concept:
Neurons are the most oxygen hungry cells in the body. They rely almost completely on aerobic metabolism and carry very little energy reserve, so a cut in oxygen supply quickly stops ATP production and cell membranes and pumps start failing. Different textbooks quote slightly different cut offs for when this becomes irreversible.

Step 3: Detailed Explanation:
Thirty seconds and fifteen seconds are far too short, brief interruptions of this length usually cause only reversible changes like fainting or transient confusion, not permanent neuron death.
Two minutes of complete hypoxia begins to produce real cellular stress, and some sources use it as a marker for when reversible injury starts to appear, but most standard teaching still places the point of no return a bit later than this.
This paper's own printed key flags the answer as uncertain and notes that many texts state the irreversible cut off is closer to 3 to 5 minutes, with commonly cited figures around 4 to 6 minutes at normal body temperature.
Among the four choices given, 8 minutes is the option the original key selected, and it sits in the same general order of magnitude, several minutes, as the commonly quoted range, even if it runs a little longer than the tightest textbook estimate.

Step 4: Final Answer:
Following the original exam key, the marked answer is 8 minutes, though standard physiology texts more often quote about 4 to 6 minutes as the point past which neuron damage becomes irreversible, a discrepancy the source paper itself flags with a question mark.