**Core Concept**
Tetanus is a bacterial infection caused by Clostridium tetani, characterized by muscle rigidity and spasms. The pathogenesis of tetanus involves the production of two main toxins: tetanospasmin and tetanolysin. Tetanospasmin is a neurotoxin that affects the nervous system, causing the clinical manifestations of the disease.

**Why the Correct Answer is Right**
The correct answer is that tetanospasmin enters the nervous system through peripheral nerve endings, where it is taken up by Schwann cells and transported to the central nervous system (CNS). This process is facilitated by a receptor called the tetanus toxin receptor, which is present on the surface of neurons. Once inside the CNS, tetanospasmin inhibits the release of neurotransmitters such as glycine and GABA, leading to hyperexcitability of neurons and the characteristic muscle spasms of tetanus.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because tetanospasmin does not enter the CNS through the bloodstream. While tetanus toxin can be absorbed systemically, the majority of the toxin remains at the site of infection.
**Option B:** Incorrect because tetanus toxin does not enter the CNS through the gastrointestinal tract. While the bacteria can infect wounds in the GI tract, the toxin does not cross the blood-brain barrier in this manner.
**Option C:** Incorrect because tetanus toxin does not enter the CNS through the skin. While the bacteria can infect wounds in the skin, the toxin is taken up by peripheral nerve endings and transported to the CNS.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that tetanus toxin is highly potent and can cause disease even in small quantities. The incubation period of tetanus can range from a few days to several weeks, depending on the dose of toxin and the site of infection.

**Correct Answer:** C.