During the filling phase of micturition, sympathetic activity keeps urine contained. Which combination correctly describes this sympathetic action on the bladder?

• A Contracts detrusor via beta-2 receptors
• B Relaxes detrusor via beta receptors and contracts internal sphincter via alpha-1 receptors ✓
• C Contracts detrusor via alpha-1 receptors and relaxes sphincter via beta-2 receptors
• D Relaxes detrusor via muscarinic receptors and contracts sphincter via nicotinic receptors

Explanation

Sympathetic fibres relax the detrusor muscle through beta receptors and simultaneously contract the internal urethral sphincter through alpha-1 receptors, promoting urine storage. Parasympathetic M3 activation does the opposite at voiding, contracting the detrusor and relaxing the sphincter. Options using muscarinic or nicotinic receptors are wrong because bladder storage control is purely adrenergic on the motor side.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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