From Surf Wiki (app.surf) — the open knowledge base

Internal urethral sphincter

Urethral sphincter muscle which constricts the internal urethral orifice

Summary

Urethral sphincter muscle which constricts the internal urethral orifice

Field	Value
Name	Internal urethral sphincter
Latin	musculus sphincter urethrae internus
Image	Illu bladder.jpg
Caption	The urinary bladder, with the position of the sphincter shown as the internal urethral orifice
Origin	The inferior ramus of the pubic bone
Insertion	Perineal raphe
Nerve	Sympathetic fibers from T10-L2 through the inferior hypogastric plexus then vesical nervous plexus
Action	Constricts proximal urethra, maintains urinary continence

The internal urethral sphincter is a urethral sphincter muscle which constricts the internal urethral orifice. It is located at the junction of the urethra with the urinary bladder and is continuous with the detrusor muscle, but anatomically and functionally fully independent from it. It is composed of smooth muscle, so it is under the control of the autonomic nervous system, specifically the sympathetic nervous system.

Function

The sphincter in a female, and its action to prevent urination

This is the primary muscle for maintaining continence of urine, a function shared with the external urethral sphincter which is under voluntary control. It prevents urine leakage as the muscle is tonically contracted via sympathetic fibers traveling through the inferior hypogastric plexus and vesical nervous plexus. Specifically, it is controlled by the hypogastric nerve, predominantly via the alpha-1 adrenergic receptor.

During urination, the preganglionic neurons of this sympathetic pathway are inhibited via signals arising in the pontine micturition center and traveling through the descending reticulospinal tracts, allowing the muscle to relax. During ejaculation, the muscle contracts to prevent reflux of semen into the urinary bladder, a phenomenon called retrograde ejaculation.

Spasms of the internal urethral sphincter are associated with penile erection. Because the internal urethral sphincter is under involuntary control, it is believed to play a role in paruresis, in which a person who perceives oneself to be under observation is unable to urinate.

References

(September 2012). "Clinical and Functional Anatomy of the Urethral Sphincter". International Neurourology Journal.
(February 2019). "Anatomy, Abdomen and Pelvis, Sphincter Urethrae". StatPearls [Internet].
(2001). "Structure and Function of the Bladder Neck".
(November 2014). "Continence and micturition: An anatomical basis". Clinical Anatomy.
(2004). "Neurophysiology of Stress Urinary Incontinence". Reviews in Urology.
(2013-02-13). "Clinically Oriented Anatomy". Lippincott Williams & Wilkins.
(April 2022). "A Comprehensive Guide to Sperm Recovery in Infertile Men with Retrograde Ejaculation". The World Journal of Men's Health.
J. B. Macalpine. (November 1934). "The Musculature of the Bladder-neck of the Male in Health and Disease". Proceedings of the Royal Society of Medicine.

Wikipedia Source

This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page.

urinary-system urethra

Want to explore this topic further?

Ask Mako anything about Internal urethral sphincter — get instant answers, deeper analysis, and related topics.

Research with Mako

Free with your Surf account

Content sourced from Wikipedia, available under CC BY-SA 4.0.

This content may have been generated or modified by AI. CloudSurf Software LLC is not responsible for the accuracy, completeness, or reliability of AI-generated content. Always verify important information from primary sources.

Report