The external sphincter muscle of female urethra is a muscle which controls
urination
Urination, also known as micturition, is the release of urine from the urinary bladder through the urethra to the outside of the body. It is the urinary system's form of excretion. It is also known medically as micturition, voiding, uresis, ...
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, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...
.
The "compressor urethrae" is also considered a distinct, adjacent muscle by some sources,
Function
The muscle helps maintain
continence
Continence may refer to:
*Fecal continence, the ability to control defecation, see Fecal incontinence
*Urinary continence, the ability to control urination, see Urinary incontinence, the involuntary excretion of urine
*Sexual continence, a synony ...
of
urine
Urine is a liquid by-product of metabolism in humans and in many other animals. Urine flows from the kidneys through the ureters to the urinary bladder. Urination results in urine being excretion, excreted from the body through the urethra.
Cel ...
along with the
internal urethral sphincter
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, but anatomically and ...
which is under control of the
autonomic nervous system
The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies viscera, internal organs, smooth muscle and glands. The autonomic nervous system is a control ...
. The external sphincter muscle prevents urine leakage as the muscle is tonically contracted via
somatic fibers that originate in
Onuf's nucleus
Onuf's nucleus is a distinct group of neurons located in the ventral part ( laminae IX) of the anterior horn of the sacral region of the human spinal cord involved in the maintenance of micturition and defecatory continence, as well as muscular ...
and pass through
sacral spinal nerves
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the ...
S2-S4 then the
pudendal nerve
The pudendal nerve is the main nerve of the perineum. It carries sensation from the external genitalia of both sexes and the skin around the anus and perineum, as well as the motor supply to various pelvic muscles, including the male or fem ...
to
synapse
In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell.
Synapses are essential to the transmission of nervous impulses from ...
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
The Pontine micturition center (PMC, also known as Barrington's nucleus) is a collection of neuronal cell bodies located in the rostral pons in the brainstem involved in the supraspinal regulation of micturition. When activated, the PMC relaxes th ...
and traveling through the
descending reticulospinal tracts.
See also
*
External sphincter muscle of male urethra
The external sphincter muscle of male urethra, also sphincter urethrae membranaceae, sphincter urethrae externus, surrounds the whole length of the membranous urethra, and is enclosed in the fascia of the urogenital diaphragm.
Its external fiber ...
*
Internal urethral sphincter
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, but anatomically and ...
*
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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