**Question:** One of the following statement about tetanus is true:

A. Tetanus is caused by a deficiency of vitamin D.
B. Tetanus is caused by a bacterial toxin produced by Clostridium tetani.
C. Tetanus affects only the upper motor neurons.
D. Tetanus affects only the lower motor neurons.

**Correct Answer: B.**

**Core Concept:**
Tetanus is a serious neurological disease caused by a neurotoxin produced by the anaerobic gram-positive bacterium Clostridium tetani. The toxin affects both upper and lower motor neurons, leading to characteristic spastic muscle contractions and stiffness.

**Why the Correct Answer is Right:**
Tetanus is caused by a specific bacterial toxin produced by C. tetani. This toxin, known as tetanospasmin, targets both upper and lower motor neurons in the peripheral and central nervous system (CNS), leading to muscle contractions and stiffness. The toxin is produced when the bacterium enters the human body through a wound, typically contaminated with soil or dust containing C. tetani spores. The toxin then enters the bloodstream and reaches the CNS, causing the clinical manifestations of tetanus.

**Why Each Wrong Option is Incorrect:**

A. Tetanus is caused by a deficiency of vitamin D. This statement is incorrect because tetanus is a bacterial infection and not related to a deficiency of any vitamin or nutrient.

C. Tetanus affects only the upper motor neurons. However, as mentioned earlier, tetanus affects both upper and lower motor neurons due to the action of tetanospasmin on these neurons.

D. Tetanus affects only the lower motor neurons. Similar to option C, this statement is incorrect as tetanus affects both upper and lower motor neurons.

**Clinical Pearl:**
Proper vaccination and wound care are crucial in preventing tetanus infection. In cases of suspected tetanus, prompt medical intervention with antibiotics, antitoxin therapy, and supportive care is essential to minimize morbidity and mortality.