In polio, the legs get paralysed and atrophied due to

Options

A. Obstruction of muscles
B. Degeneration of bones
C. Death of some muscles
D. Shrinkage of muscles.

Answer

### Step-by-Step Solution:

1. **Understanding Polio**: Polio is caused by the poliovirus, which primarily affects the nervous system. It leads to various symptoms, including paralysis, particularly in the legs.

2. **Mechanism of Paralysis**: The poliovirus targets motor neurons in the spinal cord. When these neurons are damaged or destroyed, they can no longer send signals to the muscles, leading to paralysis.

3. **Atrophy of Muscles**: Atrophy refers to the reduction in size or wasting away of muscle tissue. In polio, the paralysis caused by the virus leads to disuse of the affected muscles, which results in muscle atrophy.

4. **Evaluating Options**:
- **Obstruction of Muscles**: This option suggests a decrease in blood flow, which is not the primary cause of paralysis in polio. Thus, it is incorrect.
- **Degeneration of Bones**: This option does not relate to the effects of polio, as polio primarily affects muscles and nerves, not bones. Therefore, it is incorrect.
- **Death of Some Muscles**: This option is correct because the virus leads to the death of motor neurons, which in turn causes paralysis and muscle atrophy.
- **Shrinkage of Muscle**: While muscles may shrink due to disuse, this term does not accurately describe the process occurring in polio, making it an incorrect option.

5. **Conclusion**: The correct answer to the question is that the legs get paralyzed and atrophied due to the death of some muscles, specifically the motor neurons that control those muscles.