NEET BIOLOGY

Detailed explanation-1: -The detrusor, which is the muscle that contracts to expel urine, is comprised of randomly-oriented smooth muscle fibers and, under normal conditions, is under autonomic control.

Detailed explanation-2: -The parasympathetic nervous system stimulates the muscarinic stretch receptors in the bladder through the pelvic nerve fibers. 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.

Detailed explanation-3: -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-4: -The smooth muscle fibers are interwoven in all directions and, collectively, these are called the detrusor muscle. Contraction of this muscle expels urine from the bladder.

Detailed explanation-5: -The detrusor smooth muscle is the main muscle component of the urinary bladder wall. Its ability to contract over a large length interval and to relax determines the bladder function during filling and micturition.