The detrusor is the smooth muscle of the bladder wall responsible for both bladder storage (by relaxing during filling) and emptying (by contracting during micturition). Its unique three-layer interlacing architecture allows uniform spherical contraction to maximise voiding efficiency. Overactive detrusor (overactive bladder) is one of the most common urological conditions, affecting up to 16 percent of adults and producing urgency, frequency, and urgency urinary incontinence.
| Origin | Bladder wall — three interlacing smooth muscle layers (inner longitudinal, middle circular, outer longitudinal) that cannot be separated anatomically |
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| Insertion | Bladder base and urethral junction — the muscle forms the trigone and internal urethral sphincter at the bladder neck |
| Nerve Supply | Parasympathetic: pelvic splanchnic nerves (S2, S3, S4) — the primary micturition drive; Sympathetic: hypogastric nerve (L1, L2) — maintains continence; Somatic: pudendal nerve — the trigone and internal sphincter components |
| Blood Supply | Superior and inferior vesical arteries |
| Actions | Contracts to empty the bladder during micturition (parasympathetic); Relaxes during filling to accommodate urine at low pressure (sympathetic beta-3 receptor mediated); The trigone directs ureteral urine into the bladder preventing reflux |
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The coordination of detrusor contraction with external sphincter relaxation is mediated by the pontine micturition centre and requires intact spinal pathways — its disruption in spinal cord injury above the sacral segments produces the dyssynergia that characterises neurogenic bladder.
Overactive bladder (OAB) from involuntary detrusor contractions produces urgency incontinence managed with behavioural therapy, antimuscarinic drugs (oxybutynin, tolterodine), beta-3 agonists (mirabegron), intravesical botulinum toxin, and sacral neuromodulation in a stepwise approach. Detrusor hypocontractility from peripheral neuropathy (diabetes, multiple sclerosis) produces overflow incontinence and incomplete bladder emptying requiring intermittent catheterisation.
Not directly palpable. Assessed by urodynamic testing (cystometry) measuring bladder pressure during filling and voiding.
Involuntary detrusor contractions producing urgency, frequency, and urgency incontinence managed with antimuscarinic drugs, beta-3 agonists, and bladder botulinum toxin injection.
Underactive detrusor from neuropathy producing incomplete bladder emptying and overflow incontinence managed with clean intermittent self-catheterisation.
