Contraction of Detrusor muscle is mediated by?
**Core Concept**
The contraction of the detrusor muscle in the urinary bladder is a complex process involving the autonomic nervous system, specifically the parasympathetic division. This process is crucial for the normal micturition cycle, where the bladder contracts to expel urine.
**Why the Correct Answer is Right**
The contraction of the detrusor muscle is primarily mediated by the parasympathetic nervous system through the release of acetylcholine (ACh). ACh binds to muscarinic receptors (M2 and M3) on the detrusor muscle, leading to its contraction. This process is facilitated by the enzyme acetylcholinesterase, which breaks down ACh into choline and acetic acid, allowing for continuous stimulation of the muscarinic receptors.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the sympathetic nervous system, which is responsible for the "fight or flight" response, actually inhibits detrusor contraction and promotes bladder neck contraction through the release of noradrenaline (norepinephrine) and adrenaline.
* **Option B:** This option is incorrect because the enteric nervous system, while playing a role in the regulation of the gastrointestinal tract, is not directly involved in the contraction of the detrusor muscle.
* **Option C:** This option is incorrect because the sensory input from the bladder to the central nervous system is not directly responsible for detrusor contraction; rather, it helps to regulate the micturition cycle.
**Clinical Pearl / High-Yield Fact**
The parasympathetic nervous system's role in detrusor contraction can be remembered using the mnemonic "PANIC": Parasympathetic (P), Acetylcholine (A), Nerve Stimulation (N), Intestinal-like contractions (I), and Contraction (C).
**Correct Answer:** C. Parasympathetic nervous system.