[The striated sphincter of the urethra. 1: Recall of knowledge on the striated sphincter of the urethra]

Abstract

The first part of this report is devoted to the anatomy, nerve supply, and physiology of the striated sphincter, three subjects which greatly aroused a great deal of controversies. The conclusions of the authors are as follows. The striated sphincter of the urethra is a muscle of the perineum, arising from the cloacal sphincter. The deep transverse, bulbo-cavernous, anal sphincter, ischio-cavernous and superficial transverse muscles have the same embryological origin and together with the sphincter of the urethra form the accessory pelvic diaphragm. The embryological origin of the levator ani muscles is different. These arise from the caudal muscles and form the principal pelvic diaphragm. The striated sphincter of the urethra is unequally distributed in the male and female fetus. According to our anatomical concept, the urethral sphincter includes two structures: the para-urethral sphincter and the peri-urethral sphincter. The para-urethral sphincter form an integral part of the urethra and is distributed principally along the membranous part of urethra but extends approximately to the bladder neck and distally under the perineum aponeurosis. In the adult as in the fetus, the para-urethral striated sphincter is unequally distributed along the urethra, according to sex. In the male, it surrounds the membranous urethra and is absent from the posterior face of the prostatic urethra. By contrast, in the female, the sphincter surrounds the proximal third of the urethra and the rings are incomplete on the distal third. The peri-urethral striated sphincter includes the other muscles of the perineum and of the principal pelvic diaphragm. These two structures differ from a microscopic stand point; the para-urethral striated sphincter contains only narrow calibre slow fibers, with the absence of the neuro-muscular spindles. By contrast, the peri-urethral sphincter consists of slow and rapid fibers and contains neuro-muscular spindles. The nerve supply of the peri-urethral striated sphincter is insured by internal pudendal nerves. The para-urethral striated sphincter is supplied in great part of the same internal pudendal nerves arising from neurones situated in the nucleus of Onuf. However, the pelvic nerves may contain a group of accessory fibers from the same origin. There is no proof available as to the role played by the sympathetic nervous system. When micturition comes to an end, the para-urethral sphincter causes a constriction of the membranous urethra in the male, and single flattening of the middle part of the urethra in the female.(ABSTRACT TRUNCATED AT 400 WORDS)