Why is tetanus also called lockjaw disease?

Explanation

### Step-by-Step Solution:

1. **Understanding Tetanus**: Tetanus is an infection caused by a bacterium known as *Clostridium tetani*. This bacterium is commonly found in the environment, particularly in soil, dust, and manure.

2. **Mechanism of Infection**: The spores of *Clostridium tetani* can enter the human body through wounds or cuts. Once inside, the bacteria release toxins.

3. **Effect of Toxins**: The toxins produced by *Clostridium tetani* affect the nervous system. Specifically, they cause degeneration of motor neurons, which are responsible for controlling muscle movements.

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