Micturition and Defecation, Neuro-Chemical Control

The urinary bladder and the urethra; the rectum and the anal canal have the same embryologic anatomical source, from the cloaca. They share the same nerve supply and have systemic sensory and proprioceptors (mechanoreceptors) in the muscle responsive to mechanical changes. Toilet training switches the toilet control, supervised by the CNS, from para-sympathetic to mainly sympathetic control. Acquired high sympathetic tone at the Internal Urethral Sphincter (IUS) and the Internal Anal Sphincter (IAS) keeps both sphincters contacted and the urethra and anal canal empty and closed all the time. Voluntarily or in need with proper social circumstances, controlled by intact healthy CNS, the IUS and/or the IAS relax and the urethra and the anal canal will open to allow pass of urine, flatus and/or feces. The neurotransmitter at the sympathetic nerve endings is nor-epinephrine, which can be deficient in cases of nocturnal enuresis. The IUS and the IAS are collagen-muscle tissue cylinders. In women both sphincters are closely related to the vagina, and are subject to lacerations from vaginal delivery. Lacerated sphincters as a result of Child-Birth Trauma (CBT) become weak and cannot stand against sudden rise of abdominal pressure resulting in Urinary Incontinence (UI) and/or Fecal Incontince (FI).