Micturition is the process of urine excretion from the urinary bladder. It fills, the rugae distend and constant pressure in the bladder (intra-vesicular pressure) is maintained known as the stress-relaxation phenomenon. Micturition is also known as the voiding phase of bladder control. Bladder afferents signals ascend through the spinal cord and then project to the pontine micturition centre and cerebrum.
The pontine micturition centre also inhibits Onuf’s nucleus, with a resultant reduction in sympathetic stimulation to the internal urethral sphincter causing relaxation. Finally, a conscious reduction involuntary contraction of the external urethral sphincter from the cerebral cortex allows for distention of the urethra and the passing of urine.