Micturition occurs due to

Options

A. contraction of bladder muscles
B. contraction of urethral sphincter
C. relaxation of urethral sphincter
D. Both (1) and (3)

Answer

**Step-by-Step Solution:**

1. **Understanding Micturition**: Micturition, commonly known as urination, is the process of expelling urine from the urinary bladder through the urethra.

2. **Role of Bladder Muscles**: The bladder is a muscular sac that stores urine. When the bladder fills, stretch receptors in the bladder wall send signals to the brain, indicating the need to urinate. The contraction of the bladder muscles (detrusor muscles) is essential for micturition.

3. **Role of Urethral Sphincters**: The urethra has sphincter muscles that control the release of urine. There are two sphincters: the internal urethral sphincter (involuntary) and the external urethral sphincter (voluntary). For micturition to occur, the internal sphincter must relax to allow urine to flow from the bladder into the urethra.

4. **Combining the Actions**: Micturition involves both the contraction of the bladder muscles (to push urine out) and the relaxation of the urethral sphincters (to allow urine to exit the body).

5. **Evaluating the Options**:
- Option 1: Contraction of bladder muscles - Correct.
- Option 2: Contraction of urethral sphincter - Incorrect (it should relax).
- Option 3: Relaxation of urethral sphincter - Correct.
- Option 4: Both one and two - Incorrect (since option two is incorrect).

6. **Conclusion**: The correct answer is that micturition occurs due to the contraction of bladder muscles and the relaxation of the urethral sphincter.

**Final Answer**: Micturition occurs due to the contraction of bladder muscles and the relaxation of the urethral sphincter.

---