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A sphincter is a circular muscle that normally maintains constriction of a natural body passage or orifice and relaxes as required by normal physiological functioning. Sphincters are found in many animals. There are over 60 types in the human body, [citation needed] some microscopically small, in particular the millions of precapillary ...
In males, the internal urethral sphincter has the additional function of preventing the flow of semen into the male bladder during ejaculation. [3] Females do have a more elaborate external sphincter muscle than males as it is made up of three parts: the sphincter urethrae, the urethrovaginal muscle, and the compressor urethrae.
They're different to the extraocular muscles that are outside of the eye and control the external movement of the eye. [2] There are three intrisic ocular muscles: the ciliary muscle, pupillary sphincter muscle (sphincter pupillae) and pupillary dilator muscle (dilator pupillae). [1] [2] All of them are smooth muscles. [2]
The external urethral sphincter is a striated muscle that allows voluntary control over urination. [5] The internal sphincter, formed by the involuntary smooth muscles lining the bladder neck and urethra, receives its nerve supply by the sympathetic division of the autonomic nervous system. [6] The internal sphincter is present both in males ...
It says that there are 'more than 50' sphincters in the human body, then gives microcapillaries as an example. Shouldn't that be more than 50 *types* of sphincter? There are many millions of capillaries in the body, so 50 *instances* of sphincter cannot be correct. Syd Barrett 14:39, 23 December 2011 (UTC)
The muscle helps maintain continence of urine along with the internal urethral sphincter which is under control of the autonomic nervous system.The external sphincter muscle prevents urine leakage as the muscle is tonically contracted via somatic fibers that originate in Onuf's nucleus and pass through sacral spinal nerves S2-S4 then the pudendal nerve to synapse on the muscle.
The internal anal sphincter, IAS, or sphincter ani internus is a ring of smooth muscle that surrounds about 2.5–4.0 cm of the anal canal. It is about 5 mm thick, and is formed by an aggregation of the smooth (involuntary) circular muscle fibers of the rectum.
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 , [ 1 ] [ 2 ] but anatomically and functionally fully independent from it. [ 3 ]