Sphincter urethrae

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Sphincter urethrae membranaceae muscle
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The male urethra laid open on its anterior (upper) surface. (Region visible, but muscle not labeled.)
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Coronal section of anterior part of pelvis, through the pubic arch. Seen from in front. (Region visible, but muscle not labeled.)
Latin musculus sphincter urethrae externus urethrae masculinae, musculus sphincter urethrae membranaceae
Gray's subject #120 429
Origin: junction of the inferior rami of the pubis and ischium to the extent of 1.25 to 2 cm., and from the neighboring fasciæ
Insertion: its fellow of the opposite side
Artery:
Nerve: perineal branch of the pudendal nerve (S2,3,4)
Action: Constricts urethra, maintain urinary continence
Dorlands/Elsevier m_22/12550858

The urethral sphincter is a collective name for the muscles used to control the flow of urine from the urinary bladder. These muscles surround the urethra, so that when they contract, the urethra is closed.

  • There are two distinct areas of muscle: the internal sphincter, at the bladder neck
  • the external, or distal, sphincter

Human males have much stronger sphincter muscles than females, meaning that they can retain a large amount of urine for twice as long, as much as 800mL, i.e. "hold it".

Function

In addition to the internal and external sphincters, in the male only, the longer urethra, and the presence of the prostate gland help to close the urethra, preventing leakage.

Both sexes can use the levator ani, the voluntary muscle of the pelvic floor, to control urination. In females this muscle may be damaged, particularly by pregnancy, leading to weakness of the sphincter mechanism, and stress incontinence. Kegel exercises are a form of exercise intended to strengthen the pelvic floor muscles. They are also known as Pelvic Floor Muscle Training.

Sphincter urethrae membranaceae

The Sphincter urethrae membranaceae surrounds the whole length of the membranous portion of the urethra, and is enclosed in the fasciæ of the urogenital diaphragm.

Its external fibers arise from the junction of the inferior rami of the pubis and ischium to the extent of 1.25 to 2 cm., and from the neighboring fasciæ.

They arch across the front of the urethra and bulbourethral glands, pass around the urethra, and behind it unite with the muscle of the opposite side, by means of a tendinous raphé.

Its innermost fibers form a continuous circular investment for the membranous urethra.

Additional images

External links

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant.


de:Musculus urethralis


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