Editing Urination (section)

====Storage phase====
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}}|width=210|caption=[[Tiger]]s and [[lion]]s raise their tails while urinating.<ref name="Schulz">{{Cite book |last=Schulz |first=Stefan |url=https://books.google.com/books?id=MHza8Kvo5T8C&dq=urine&pg=PA249 |title=The Chemistry of Pheromones and Other Semiochemicals II |date=2005-01-07 |publisher=Springer Science & Business Media |isbn=978-3-540-21308-6 |language=en}}</ref><ref>Asa, Cheryl S. [https://academic.oup.com/icb/article-pdf/33/2/167/361050/33-2-167.pdf "Relative contributions of urine and anal-sac secretions in scent marks of large felids."] American Zoologist 33.2 (1993): 167-172.</ref>}}During storage, bladder pressure stays low, because of the bladder's highly compliant nature. A plot of bladder (intravesical) pressure against the depressant of fluid in the bladder (called a [[cystometrogram]]), will show a very slight rise as the bladder is filled. This phenomenon is a manifestation of the [[Young–Laplace equation|law of Laplace]], which states that the pressure in a spherical viscus is equal to twice the wall tension divided by the radius. In the case of the bladder, the tension increases as the organ fills, but so does the radius. Therefore, the pressure increase is slight until the organ is relatively full. The bladder's smooth muscle has some inherent contractile activity; however, when its nerve supply is intact, stretch receptors in the bladder wall initiate a reflex contraction that has a lower threshold than the inherent contractile response of the muscle.

Action potentials carried by sensory neurons from stretch receptors in the urinary bladder wall travel to the sacral segments of the spinal cord through the pelvic nerves.<ref name="yoshimura" /> Since bladder wall stretch is low during the storage phase, these afferent neurons fire at low frequencies. Low-frequency afferent signals cause relaxation of the bladder by inhibiting sacral parasympathetic preganglionic neurons and exciting lumbar sympathetic preganglionic neurons. Conversely, afferent input causes contraction of the sphincter through excitation of Onuf's nucleus, and contraction of the bladder neck and urethra through excitation of the sympathetic preganglionic neurons.

[[Diuresis]] (production of urine by the kidney) occurs constantly, and as the bladder becomes full, afferent firing increases, yet the micturition reflex can be voluntarily inhibited until it is appropriate to begin voiding.