Abstract
The anal function is controlled by the smooth and striated sphincter muscles which are innervated with the autonomic and somatic nerves respectively. Anatomically, the anorectal angle which is formed by an adequate forward pull of the puborectalis muscle is most important. In manometric study, resting pressure is a function mainly of the internal anal sphincter, and squeeze pressure is a function of the external anal sphincter. In electromyographical study, the external anal sphincter reveals cotinuous or basal electrical potentials in the resting state which is an unusual phenomenon for skeletal muscle. This feature means the anal canal can maintaine in continuous tonic state all the time without fatigue. The same feature is provided as the type 1 fiber predominance by the histochemical staining of the external anal shincter muscle. An assessment employing basic anatomical and physiological features of the anal canal may supply valuable information directly affecting diagnosis and treatment for various anal deseases.
