ANATOMY

Detailed explanation-1: -When urine fills the bladder, the M3 receptors located within the bladder become stretched and stimulated, which leads to the contraction of the detrusor muscle for urination. At the same time, the parasympathetic fibers inhibit the internal urethral sphincter, which causes relaxation allowing for bladder emptying.

Detailed explanation-2: -When the bladder is full of urine, stretch receptors in the bladder wall trigger the micturition reflex. The detrusor muscle that surrounds the bladder contracts. The internal urethral sphincter relaxes, allowing for urine to pass out of the bladder into the urethra.

Detailed explanation-3: -The sphincter is a muscle around the opening of the bladder. It squeezes to prevent urine from leaking into the urethra. This is the tube that urine passes through from your bladder to the outside. The bladder wall muscle relaxes so the bladder can expand and hold urine.

Detailed explanation-4: -As your bladder fills, nerve signals sent to your brain eventually trigger the need to urinate. When you urinate, these nerve signals coordinate the relaxation of the pelvic floor muscles and the muscles of the urethra (urinary sphincter muscles). The muscles of the bladder tighten (contract), pushing the urine out.