The outline of principal events of urination is given below in random manner.
(i). Stretch receptors on the wall of urinary bladder send signals to the CNS.
(ii). The bladder fills with urine and becomes distended.
(iii). Micturition.
(iv). CNS passes on motor messages to initiate the contraction of smooth muscles of bladder and simultaneous relaxation of urethral sphincter.
The correct sequence of the event is

Options

A. (i) `to` (ii) `to` (iii) `to` (iv)
B. `(iv)to(iii)to(ii)to(i)`
C. `(ii)to(i)to(iv)to(iii)`
D. `(iii)to(ii)to(i)to(iv)`

Answer

To determine the correct sequence of events in the process of urination (micturition), we can analyze the given steps systematically:

1. **Bladder Filling**: The process begins with the bladder filling with urine. As it fills, it becomes distended. This is the initial stage where urine is collected in the bladder.

**Step 1**: The bladder fills with urine and becomes distended. (ii)

2. **Activation of Stretch Receptors**: As the bladder becomes distended, stretch receptors located on the wall of the urinary bladder are activated. These receptors detect the stretching of the bladder wall due to the presence of urine.

**Step 2**: Stretch receptors on the wall of the urinary bladder send signals to the CNS. (i)

3. **CNS Response**: Once the stretch receptors send signals to the central nervous system (CNS), the CNS processes this information and sends motor messages back to the bladder.

**Step 3**: CNS passes on motor messages to initiate the contraction of smooth muscles of the bladder and simultaneous relaxation of the urethral sphincter. (iv)

4. **Micturition**: The final step is the act of micturition itself, where the bladder contracts to expel urine, and the sphincter relaxes to allow urine to flow out.

**Step 4**: Micturition. (iii)

Putting it all together, the correct sequence of events is:
(ii) → (i) → (iv) → (iii)

Thus, the correct order is:
1. The bladder fills with urine and becomes distended. (ii)
2. Stretch receptors on the wall of urinary bladder send signals to the CNS. (i)
3. CNS passes on motor messages to initiate the contraction of smooth muscles of bladder and simultaneous relaxation of urethral sphincter. (iv)
4. Micturition. (iii)