THORAX ABDOMEN AND PELVIS

Detailed explanation-1: -Smooth muscle stretch initiates the micturition reflex by activating stretch receptors in the bladder wall. This autonomic reflex causes the detrusor muscle to contract and the internal urethral sphincter muscle to relax, allowing urine to flow into the urethra.

Detailed explanation-2: -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-3: -The internal sphincter muscles of the bladder neck and urethra stay closed until your brain sends signals to urinate. The external sphincter muscles surround the internal sphincter and provide extra pressure to keep the urethra closed.

Detailed explanation-4: -Introduction. Urination or micturition removes metabolic products and toxic wastes filtered from the kidneys and is a vital function of the human body. The micturition reflex requires a complex network of signals between the nervous system and the urinary tract system.