RESUMEN
Beginning at the sacral plexus the nerve disposition can be found to follow two modalities: first disposition in 2/3 of all cases having a cranial nerve branch for the elevator portion and a caudal nerve branch for the sphincter portion; second disposition in 1/3 of all cases having a branch divided in its terminal part into 2 ramus branches, one for the elevator portion and one for the sphincter portion. On the average the nerve contains 539 fibers of which 73% are myelinated and 27% non myelinated. The fibrillar content is identical for both branches of either disposition.
Asunto(s)
Canal Anal/inervación , Canal Anal/embriología , Feto , Humanos , Plexo Lumbosacro/anatomía & histología , Persona de Mediana Edad , Músculos/inervación , Fibras Nerviosas/ultraestructura , Fibras Nerviosas Mielínicas/ultraestructura , Neurofibrillas/ultraestructuraRESUMEN
The study was performed using 45 pelvic half section specimens (41 fetal ones and four adults). The macroscopic dissection followed the nerve branches from their spinal roots up to the external anal sphincter. Three nerve branches were found: the anterior ramus arising from the external perineal nerve, the inferior rectal nerve and an independent posterior branch. The anterior and the inferior rectal nerve branches always emerged from the pudendal plexus. The posterior branch arising either from S4 or from the inferior rectal nerve was only found in (31%) of our cases. Five anatomical distributions are described, percentages of every type notified. The fibre content of these nerve bundle branches was evaluated through histological sections using Heidenhain's azan stain and Luxol fast blue. The branches consisted of 2,896 to 2,137 fibres, 20% of them being unmyelinated and 80% containing various myelinated fibres. The nomenclature of these nerve branches has to be debated. The terms of anterior, middle and posterior anal nerves seem more suitable.