detrusormuscle

The detrusor muscle is a thick bundle of smooth muscle fibers that forms the wall of the urinary bladder. It is responsible for bladder contraction during micturition and for maintaining bladder storage by relaxing during filling. The detrusor comprises multiple smooth muscle layers arranged in interwoven directions, allowing it to generate coordinated contractions while accommodating large volume changes.

Anatomically, the detrusor lies between the mucosa and the outer bladder layers. Its muscle fibers receive autonomic innervation from the inferior hypogastric plexus. Parasympathetic fibers from the pelvic nerves promote contraction via acetylcholine; sympathetic fibers from the hypogastric plexus promote relaxation through beta-adrenergic receptors and help regulate the internal urethral sphincter. Somatic control of the external urethral sphincter is via the pudendal nerve.

Physiologically, during storage, sympathetic activity dominates and detrusor tone remains low, while the internal sphincter stays contracted. As the bladder fills and afferent signals rise, a micturition reflex is triggered, increasing parasympathetic activity, causing detrusor contraction and relaxation of the internal sphincter, with voluntary relaxation of the external sphincter enabling urination.

Pathologies involving the detrusor include detrusor overactivity, detrusor underactivity, and detrusor hypertrophy associated with bladder outlet obstruction. Treatments range from antimuscarinic agents and beta-adrenergic agonists to botulinum toxin injections into the detrusor, sacral neuromodulation, and surgical options in refractory cases.