The external sphincter muscle of the female urethra is a muscle which controls
urination
Urination is the release of urine from the bladder through the urethra in Placentalia, placental mammals, or through the cloaca in other vertebrates. It is the urinary system's form of excretion. It is also known medically as micturition, v ...
in females. The muscle fibers arise on either side from the margin of the inferior ramus of the pubis. They are directed across the pubic arch in front of the urethra, and pass around it to blend with the muscular fibers of the opposite side, between the urethra and vagina.
The term "urethrovaginal sphincter" ("sphincter urethrovaginalis") is sometimes used to describe the component adjacent to the
vagina
In mammals and other animals, the vagina (: vaginas or vaginae) is the elastic, muscular sex organ, reproductive organ of the female genital tract. In humans, it extends from the vulval vestibule to the cervix (neck of the uterus). The #Vag ...
.
The "compressor urethrae" is also considered a distinct, adjacent muscle by some sources,
Function
The muscle helps maintain
continence of
urine
Urine is a liquid by-product of metabolism in humans and many other animals. In placental mammals, urine flows from the Kidney (vertebrates), kidneys through the ureters to the urinary bladder and exits the urethra through the penile meatus (mal ...
along with the
internal urethral sphincter which is under control of the
autonomic nervous system
The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...
. 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
The pudendal nerve is the main nerve of the perineum. It is a Mixed nerve, mixed (motor and sensory) nerve and also conveys Sympathetic nervous system, sympathetic Autonomic nervous system, autonomic fibers. It carries sensation from the exter ...
to
synapse
In the nervous system, a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending o ...
on the muscle.
Voiding urine begins with voluntary relaxation of the external urethral sphincter. This is facilitated by inhibition of the somatic neurons in Onuf's nucleus via signals arising in the
pontine micturition center and traveling through the
descending reticulospinal tracts.
See also
*
External sphincter muscle of male urethra
*
Internal urethral sphincter
*
Levator ani
The levator ani is a broad, thin muscle group, situated on either side of the pelvis. It is formed from three muscle components: the pubococcygeus, the iliococcygeus, and the puborectalis.
It is attached to the inner surface of each side of the ...
References
Urinary system
Mammal female reproductive system
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