Final answer:
Urination without conscious control typically occurs when the bladder is filled with between 300 mL and 400 mL, due to the loss of voluntary constraint as urged by the micturition reflex.
Step-by-step explanation:
When the bladder is filled with between 300 mL and 400 mL urination occurs without conscious control in a healthy, average person. The micturition reflex involves an interplay of involuntary and voluntary actions by the internal and external urethral sphincters. As the bladder fills, an urge to void is first felt at approximately 150 mL but is easily controlled. As bladder volume increases, these urges become harder to ignore until it reaches a threshold where voluntary constraint fails, commonly between 300 to 400 mL, leading to incontinence. The bladder's capacity typically ranges up to 500-600 mL, indicating that urgent sensations happen well before maximum capacity is reached. This mechanism is also supported by different muscles including the detrusor muscle and aided by voluntary contractions of abdominal skeletal muscles especially as the bladder's strength diminishes with age.