detrusore

Detrusor, or the detrusor muscle, is the smooth muscle layer of the urinary bladder wall. It forms the muscularis propria and contracts to expel urine during micturition. The detrusor is organized into interlacing smooth muscle bundles arranged in inner longitudinal, middle circular, and outer longitudinal orientations, allowing the bladder wall to thicken uniformly when contracting.

Innervation and control begin with the autonomic nervous system. Parasympathetic fibers from the pelvic nerves (S2–S4) release acetylcholine, activating muscarinic M3 receptors to induce detrusor contraction. Sympathetic input from the hypogastric nerve (L1–L2) promotes bladder filling by relaxing the detrusor via beta-adrenergic receptors. Somatic motor control of the external urethral sphincter is provided by the pudendal nerve, enabling voluntary control of urination. The micturition reflex integrates bladder wall stretch signals with higher brain centers to coordinate contraction and sphincter relaxation.

Clinical relevance arises from disorders of detrusor function. Detrusor overactivity involves involuntary contractions during filling, contributing to urge incontinence; it can occur with aging, neurological disease, or bladder outlet obstruction. Treatments include behavioral therapy, antimuscarinic agents or beta-3 agonists (such as mirabegron), intradetrusor botulinum toxin injections, and, in selected cases, neuromodulation. Detrusor underactivity or acontractile detrusor leads to impaired bladder emptying and urinary retention, sometimes requiring intermittent catheterization. Urodynamic studies are used to assess detrusor function and guide management.