**Core Concept**
Tetanus toxin is a potent neurotoxin that causes muscle rigidity and spasms by blocking the release of neurotransmitters, such as glycine and GABA, in the spinal cord and brainstem. This toxin is responsible for the characteristic symptoms of tetanus, including muscle stiffness, spasms, and rigidity.

**Why the Correct Answer is Right**
The correct answer is related to the mechanism of action of tetanus toxin. Tetanus toxin works by cleaving the synaptobrevin protein, which is a key component of the synaptic vesicle release machinery. This cleavage event prevents the release of neurotransmitters, such as glycine and GABA, into the synaptic cleft, leading to muscle rigidity and spasms. The toxin does not affect the release of acetylcholine, which is a neurotransmitter involved in the transmission of nerve impulses to muscles.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is true that tetanus toxin causes muscle rigidity and spasms. The toxin works by blocking the release of neurotransmitters in the spinal cord and brainstem, leading to these characteristic symptoms.

**Option B:** This option is incorrect because it is true that tetanus toxin is a potent neurotoxin that can cause muscle rigidity and spasms. The toxin works by cleaving the synaptobrevin protein, which is a key component of the synaptic vesicle release machinery.

**Option D:** This option is incorrect because it is true that tetanus toxin is caused by the bacterium Clostridium tetani. The bacterium produces the tetanus toxin, which is responsible for the characteristic symptoms of tetanus.

**Clinical Pearl / High-Yield Fact**
Tetanus toxin is a potent neurotoxin that can cause muscle rigidity and spasms by blocking the release of neurotransmitters in the spinal cord and brainstem. The toxin works by cleaving the synaptobrevin protein, which is a key component of the synaptic vesicle release machinery.

**Correct Answer: None**