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The sphincter urethrae, or urethral sphincter, controlling the exit of urine from the body. At the anus, there are two anal sphincters which control the exit of feces from the body, the internal anal sphincter and external anal sphincter. The inner sphincter is involuntary and the outer is voluntary.
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.
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.
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 ciliary muscle is attached to the zonular fibers and the zonular fibers are the suspensory ligaments of the lens. [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 ...
[8] [9] [10] Below this, muscles and their fascia converge and become part of the perineal body. The lower vagina is attached to the perineal body by attachments from the pubococcygeus, perineal muscles, and the anal sphincter. The perineal body is made up of smooth muscle, elastic connective tissue fibers, and nerve endings. Above the perineal ...
There are many reasons why the male G-spot often remains unexplored, especially by cis, heterosexual men. For one, there’s the social script that anal sex is “gay” that many people grew up with.
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.