Final answer:
The detrusor muscle's function during micturition is to contract and empty the bladder. It operates under the control of both autonomic and somatic nervous systems, with voluntary abdominal muscle contractions providing additional force for bladder emptying when necessary.
Step-by-step explanation:
The function of the detrusor muscle in micturition is that it contracts to empty the bladder. The detrusor muscle, made up of smooth muscle fibers, works in conjunction with both the autonomic and somatic nervous systems to manage the process of urination. As the bladder fills with urine, the detrusor muscle relaxes, a reaction controlled by the autonomic system. Once the need to urinate arises, conscious signals from the somatic nervous system stimulate the detrusor muscle to contract while the internal urethral sphincter relaxes, thus expelling urine from the bladder into the urethra.
This muscle's contraction force is greater in younger individuals and can decline with age. However, abdominal skeletal muscles can be voluntarily contracted to increase intra-abdominal pressure and help empty the bladder more forcefully, a mechanism also utilized during defecation and childbirth. On a physiological level, filling of the bladder activates stretch receptors, triggering a spinal reflex that results in detrusor muscle contraction and coordinated relaxation of the urethral sphincters, effectively leading to urination.