(anatomy) A smooth muscle in the wall of the bladder that relaxes to allow urine to be stored and contracts to expel it; often used attributively.
2009, Christopher R. Chapple, Scott A. MacDiarmid, Anand Patel, Urodynamics Made Easy, Elsevier (Churchill Livingstone), 3rd Edition, page 88,
During voiding the patient's bladder should empty completely with a maximum detrusor pressure of 25–50 cm H₂O.