Long refractory period is present in

Options

A. Smooth muscles
B. Cardiac muscles
C. Striated muscles
D. None of these

Answer

**Step-by-Step Solution:**

1. **Understanding Refractory Period**: The refractory period is defined as the time during which a muscle or nerve cell is unable to respond to a stimulus. This property is crucial for the proper functioning of excitable tissues like muscles and neurons.

2. **Types of Refractory Periods**: There are two types of refractory periods:
- **Absolute Refractory Period**: This is the time during which no stimulus can elicit a response, which includes the phases of depolarization and repolarization.
- **Relative Refractory Period**: This phase occurs after the absolute refractory period and can respond to a stronger-than-normal stimulus, which involves hyperpolarization.

3. **Refractory Period in Different Muscle Types**:
- **Skeletal Muscle**: The refractory period is relatively short, approximately 0.002 to 0.005 seconds.
- **Cardiac Muscle**: The refractory period is significantly longer, ranging from 0.1 to 0.2 seconds.

4. **Importance of Long Refractory Period in Cardiac Muscle**: The long refractory period in cardiac muscle is essential to prevent tetanus (a sustained contraction). If the refractory period were shorter, the heart would not have enough time to relax and refill with blood before the next contraction, which could lead to inefficient pumping and potential cardiac issues.

5. **Conclusion**: Based on the information gathered, the long refractory period is specifically present in cardiac muscles.

**Final Answer**: Long refractory period is present in cardiac muscles.

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