WordNet

make ones way by force; "He muscled his way into the office"
animal tissue consisting predominantly of contractile cells (同)muscular_tissue
one of the contractile organs of the body (同)musculus
authority or power or force (especially when used in a coercive way); "the senators used their muscle to get the party leader to resign"
a ring of muscle that contracts to close an opening (同)anatomical sphincter, sphincter_muscle
duct through which urine is discharged in most mammals and which serves as the male genital duct

PrepTutorEJDIC

〈U〉(動物体の組織としての)『筋肉』,筋(きん);〈C〉(体の各部を動かす)筋肉 / 〈U〉力,(特に)筋力,腕力 / 《俗に》(…に)強引に割り込む《+『in on』(『into, through』)+『名』》
括約筋(かつやくきん)
尿道
筋肉の,筋力のある / 力ずくの

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/10/15 19:13:32」(JST)

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The urethral sphincter is one of two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are the male or female external urethral sphincter and the internal urethral sphincter. When either of these muscles contracts, the urethra is sealed shut.

The external urethral sphincter originates at the ischiopubic ramus and inserts into the intermeshing muscle fibers from the other side. It is controlled by the deep perineal branch of the pudendal nerve. Activity in the nerve fibers constricts the urethra.

The internal sphincter muscle of urethra: located at the bladder's inferior end and the urethra's proximal end at the junction of the urethra with the urinary bladder. The internal sphincter is a continuation of the detrusor muscle and is made of smooth muscle, therefore it is under involuntary or autonomic control. This is the primary muscle for prohibiting the release of urine.

The female or male external sphincter muscle of urethra (sphincter urethrae): located at the bladder's distal inferior end in females and inferior to the prostate (at the level of the membranous urethra) in males is a secondary sphincter to control the flow of urine through the urethra. Unlike the internal sphincter muscle, the external sphincter is made of skeletal muscle, therefore it is under voluntary control of the somatic nervous system.

Dissection of prostate showing the fibers of the external sphincter surrounding the membranous urethra and partially cradling the inferior portion of the prostate.

Sex differences

In males and females, both internal and external urethral sphincters function to inhibit the release of urine. In males, the internal sphincter muscle of urethra functions to prevent reflux of seminal fluids into the male bladder during ejaculation.

Females do have a more elaborate external sphincter muscle than males as it is made up of three parts: the sphincter urethrae, urethrovaginal muscle, and the compressor urethrae. The urethrovaginal muscle fibers wrap around the vagina and urethra and contraction leads to constriction of both the vagina and the urethra. The origin of the compressor urethrae muscle is the right and left inferior pubic ramus and it wraps anteriorly around the urethra so when it contracts it squeezes the urethra against the vagina. The external urethrae, like in males, wraps solely around the urethra.^{[citation needed]}

Function

The internal urethral sphincter provides involuntary control of urination. The external urethral sphincter provides voluntary control of urination.

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

External links

Anatomy figure: 41:06-04 at Human Anatomy Online, SUNY Downstate Medical Center - "Muscles of the female urogenital diaphragm (deep perineal pouch) and structures located inferior to it."

UpToDate Contents

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English Journal

The urethral rhabdosphincter, levator ani muscle, and perineal membrane: a review.

Hinata N1, Murakami G2.
BioMed research international.Biomed Res Int.2014;2014:906921. doi: 10.1155/2014/906921. Epub 2014 Apr 27.
Detailed knowledge of the anatomy of the rhabdosphincter and adjacent tissues is mandatory during urologic surgery to ensure reliable oncologic and functional outcomes. To characterize the levator ani (LA) function for the urethral sphincter, we described connective tissue morphology between the LA
PMID 24877147

Somatic innervation of the feline lower urinary tract.

Yoo PB1, Woock JP, Grill WM.
Brain research.Brain Res.2008 Dec 30;1246:80-7. doi: 10.1016/j.brainres.2008.09.053. Epub 2008 Sep 30.
Electrical stimulation of pudendal nerve sensory pathways can evoke excitatory bladder reflexes. However, the precise peripheral innervation pattern of these somatic fibers remains unclear. In adult male cats, we investigated pudendal nerve innervation of the lower urinary tract (LUT) by employing a
PMID 18848924

Female perineal membrane: a study using pelvic floor semiserial sections from elderly nulliparous and multiparous women.

Kato M1, Matsubara A, Murakami G, Abe S, Ide Y, Sato I, Usui T.
International urogynecology journal and pelvic floor dysfunction.Int Urogynecol J Pelvic Floor Dysfunct.2008 Dec;19(12):1663-70. doi: 10.1007/s00192-008-0701-0. Epub 2008 Aug 8.
To describe the architecture and topohistology of the female perineal structures, especially the perineal membrane (PM), we examined frontal sections (one side) and horizontal or transverse sections (another side) of 15 bisectioned pelvic floors. The PM, notably comprising elastic fibers, extended m
PMID 18688559