Final answer:
The Sphincter urethrovaginalis is a muscle involved in the voluntary control of urine in females. Its exact origin and insertion are less defined, but its function is to assist the external urethral sphincter, which is controlled by the pudendal nerve.
Step-by-step explanation:
The Sphincter urethrovaginalis is a muscle in females that assists in the voluntary control of the urethra, contributing to urinary continence. The terms O and I you mentioned typically refer to the muscle's origin and insertion points; however, for the urethrovaginal sphincter, specific origin and insertion points are less commonly detailed and the muscle's function is more widely discussed. The urethrovaginal sphincter works in concert with the external urethral sphincter to control the outflow of urine through the urethra. This control is possible due to the innervation from the pudendal nerve, which arises from the sacral region of the spinal cord, traveling through the S2-S4 nerves of the sacral plexus.
The urinary system in both males and females includes integral components such as the internal urinary sphincter and the urethra, lined by various types of epithelia, which differ along its tract. In females, the urethra is relatively short, thus imparting a greater susceptibility to urinary tract infections (UTIs) as compared to the longer male urethra. Overall, the urethrovaginal sphincter is a crucial part of the urinary system, helping to maintain continence and to regulate the passage of urine.