title: On the etiology of the electric activity of the external anal and urethral sphincters.
abstract: In a previous study, the external anal sphincter (EAS) in dogs, known to consist of skeletal muscle fibers, was proved to contain bundles of smooth muscle fibers in between as well.
  
  
  OBJECTIVE
  Cause of electric activity in the external anal and urethral sphincters is not known; the current study investigated this point.
  
  
  METHODS
  Slices from external anal and urethral sphincters of 21 cadavers (12 male, 9 female). Eighth were fully and mat wide neonates, 13 were adults, were stained with hematoxylin and eosin, Masson's trichrome and succinic dehydrogenase, and examined microscopically. Eighteen healthy volunteers, electromyography activity of their external anal and urethral sphincters was recorded at rest, on coughing, after pudendal nerve block and after drotaverine administration, (a smooth muscle relaxant). Anal and urethral pressures were also measured.
  
  
  RESULTS
  Microscopic studies have shown that both external anal and urethral sphincters were formed of bundles of smooth muscle fibers present in between the skeletal muscle fibers. Bilateral pudendal nerve block did not abolish the external anal or the urethral sphincters electromyography activity at rest, or on coughing, and did not cause significant anal or urethral pressure changes (p > .05). Drotaverine administration lead to disappearance of the electromyography activity and significant decline of the anal and urethral pressures (p < .05). The results were reproducible when the tests were repeated in the same subject.
  
  
  CONCLUSIONS
  Histologic examination revealed the presence of smooth muscle fibers, between the skeletal fibers of the external anal and urethral sphincters. Evidence suggests that the smooth muscle fibers are the source of the electric activity of the sphincters and might explain some physiologic phenomena such as the external anal contraction on rectal distension or on coughing.
authors: 1Faculty of Medicine, Cairo University, Cairo, Egypt and.
authors: Ali A
authors: AA
authors: Shafik
authors: Ismail A
authors: IA
authors: Shafik
authors: Olfat
authors: O
authors: El Sibai
mesh_terms: D000293:Adolescent; D000328:Adult; D001003:Anal Canal / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D000818:Animals; D002648:Child; D004285:Dogs; D004576:Electromyography; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000502:physiology; D009407:Nerve Block; D010208:Papaverine / Q000031:analogs & derivatives / Q000494:pharmacology; D010276:Parasympatholytics / Q000494:pharmacology; D014521:Urethra / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D055815:Young Adult
chemical_list: D010276:Parasympatholytics; C005317:drotaverin; D010208:Papaverine
keywords: continence; electromyography; muscle fibers; reflex, anal urethral; skeletal; smooth