The urinary sphincter is a group of muscles located at the base of the bladder that controls the release of urine from the body. It consists of two main parts: the internal urinary sphincter, which is involuntary and helps keep urine in the bladder, and the external urinary sphincter, which is voluntary and allows a person to control when to urinate. These muscles work together to maintain continence, preventing leakage until an appropriate time for urination. When the bladder fills, signals are sent to the brain, prompting the sphincters to relax and allow urine to flow through the urethra and out of the body.