Sudden sustained involuntary contraction of muscles is called  

Options

A. fatigue
B. twitch
C. tonus
D. spasm

Answer

To answer the question "Sudden sustained involuntary contraction of muscles is called," we can follow these steps:

### Step 1: Understand the Terms
- **Fatigue**: This refers to a decrease in the ability of muscles to perform over time, leading to exhaustion. It is not a contraction but rather a state after prolonged activity.
- **Twitch**: This is a small, involuntary contraction of a muscle. It is brief and does not represent a sustained contraction of a larger muscle group.
- **Tonus**: This refers to a state of continuous and passive partial contraction of muscles, which helps maintain posture and readiness for action. It is not a sudden contraction.
- **Spasm**: This is an involuntary contraction of a muscle that is sudden and can be prolonged. It can cause discomfort or pain and is often a response to various stimuli.

### Step 2: Analyze the Options
- **Fatigue**: Incorrect, as it describes a state rather than a contraction.
- **Twitch**: Incorrect, as it refers to a brief contraction, not sustained.
- **Tonus**: Incorrect, as it describes a continuous state rather than a sudden contraction.
- **Spasm**: Correct, as it describes a sudden and sustained involuntary contraction.

### Step 3: Conclusion
The correct answer to the question is **spasm**, as it accurately describes a sudden sustained involuntary contraction of muscles.

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