INTENAL AND EXTERNAL URETHRAL SPHINCTER

The term urethral sphincter refers to one of two muscles used to control the exit of urine in the urinary bladder through the urethra. The two muscles are the external urethral sphincter, which is present in both
men and women, and the internal urethral
sphincter, which is present only in men.
When either of these muscles contract, the urethra is sealed shut. The external urethral sphincter originates
at the ischiopubic ramus and inserts into the intermeshing muscle fibers from the
other side. It is controlled by the deep
perineal branch of the pudendal nerve. Activity in the nerve fibers constricts the
urethra. The internal sphincter muscle of urethra: located at the bladder's inferior end and
the urethra's proximal end at the
junction of the urethra with the urinary
bladder. The internal sphincter is a
continuation of the detrusor muscle and is made of smooth muscle, therefore it is under involuntary or autonomic control. This is the primary muscle for
prohibiting the release of urine. The external sphincter muscle of urethra (sphincter urethrae): located at the
bladder's distal inferior end in females
and inferior to the prostate (at the level
of the membranous urethra) in males is a secondary sphincter to control the
flow of urine through the urethra. Unlike
the internal sphincter muscle, the
external sphincter is made of skeletal muscle, therefore it is under voluntary control of the somatic nervous system. Gender differences Main articles: External sphincter muscle of male urethra and External sphincter muscle of female urethra Despite common misconceptions, human
males do not have stronger urethral
sphincter muscles than females, nor are
there any noticeable capacity differences
in the bladders. Anatomically, females
have to urinate more frequently because their bladders share space with the uterus
and vagina in the anterior wall. In
actuality, females do not have an internal
urethral sphincter muscle. This muscle's
function is to prevent reflux of seminal
fluids into the male bladder during ejaculation. In males the bladder does not
share space with any reproductive organs. Females do have a more elaborate external
sphincter muscle than men as it is made up
of three parts, the sphincter urethrae,
urethrovaginal muscle, and the compressor
urethrae. The urethrovaginal muscle fibers
wrap around the vagina and urethra and contraction leads to constriction of both the
vagina and the urethra. The origin of the
compressor urethrae muscle is the right
and left inferior pubic ramus and it wraps anteriorly around the urethra so when it
contracts it squeezes the urethra against
the vagina. The external urethrae, like in
males, wraps solely around the urethra.[citation needed] Function In addition to the internal and external
sphincters, in males the urethra extends to
the end of the penis, where it opens up to the outside. The levator ani, the voluntary muscle of the pelvic floor, can be used to control urination. In females this muscle may be damaged, most commonly by childbirth,
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.