Detrusor muscle is found in the bladder. Contraction of the detrusor muscle compresses the urinary bladder and expels it's contents into the urethra.
Trigone acts as a funnel that channels urine into the urethra when the urinary bladder contracts.
Internal urethral sphincter is located in the neck of the urinary bladder. It provides involuntary control over the discharge of urine from the bladder.
External urethral sphincter, on the other hand is located where the urethra passes through the urogenital diaphragm and unlike the internal urethra sphincter it is under voluntary control.
