The bladder is an extraperitoneal muscular urine reservoir that lies behind the pubic symphysis in the pelvis. A normal bladder functions through a complex coordination of musculoskeletal, neurologic, and psychological functions that allow filling and emptying of the bladder contents. The prime effector of continence is the synergic relaxation of detrusor muscles and contraction of the bladder neck and pelvic floor muscles. This occurs during bladder filling and urine storage. See the image below.
Gross anatomy of the bladder.
The normal adult bladder accommodates 300-600 mL of urine. A central nervous system response is usually triggered when the volume reaches 400 mL and is perceived as the sensation of bladder fullness and the need to void. However, urination can be prevented by cortical suppression of the peripheral nervous system or by voluntary contraction of the external urethral sphincter.