Final answer:
The involuntary sphincter at the bladder exit is the internal urethral sphincter, controlled by the autonomic nervous system.
Step-by-step explanation:
The sphincter located at the bladder exit and is involuntary is the internal urethral sphincter. It consists of smooth muscle at the juncture of the bladder and urethra and relaxes as the bladder fills to allow urine to pass into the urethra. The internal sphincter operates under the control of the autonomic nervous system and is not under conscious control, which distinguishes it from the external urethral sphincter—a striated muscle controlled by the somatic nervous system that is under voluntary control.