Library · Physiology
Micturition
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Micturition is urinating. It sounds simple, but the body has to coordinate several things to release the urine the kidney has filtered, and it does so with a network of signals that runs from the nervous system to the urinary tract and back.
The alert comes from the bladder itself. Its muscle is called the detrusor, and it sends more and more signals upward to the pontine micturition center, which sits in the brainstem, the lower part of the brain that connects to the spinal cord. Then two things happen at the same time. The pelvic floor and the sphincters, the rings of muscle that close off the outlet, relax voluntarily. And acetylcholine, a chemical messenger released by nerves, makes the detrusor contract. Emptying takes two movements at once: the outlet opens and the wall pushes.
There is also a safeguard for the rest of the time. It is called the guarding reflex, and it is what keeps you continent when the pressure inside the bladder rises suddenly: when you cough or sneeze.
In brief
Micturition expels the urine the kidney has filtered, and the reflex requires a network of signals between the nervous system and the urinary tract.
Emptying begins when the detrusor signals the pontine micturition center; the pelvic floor and sphincters relax and acetylcholine contracts the bladder.
Emptying takes two things at once: the outlet opens and the wall pushes.
The guarding reflex maintains continence when bladder pressure rises suddenly with coughing or sneezing.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Urination, StatPearlsPublished
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