Chapter 1 16 Another study by Penninckx et al.18 found that the estimated anal resting tone was generated by the nerve-induced activity in the IAS for 45%, myogenic tone for 10%, tonic activity of the EAS (30%) and anal haemorrhoidal plexus for 15%. The perineal body lies between the upper end of the anterior anal canal and the posterior wall of the urethral membrane. It serves as an intersection of the EAS, the bulbospongiosus muscle, the external urethral sphincter, and the levator ani muscle. The pelvic floor is a multifunctional complex of muscle fibers, fascia, ligaments, and connective tissue that form a hammock at the bottom of the abdomino-pelvic cavity. “Left inferior view of levator ani and external anal sphincter muscles -English labels” at AnatomyTOOL.org by Ron Slagter, LUMC and Marco DeRuiter, LUMC, license: Creative Commons Attribution-NonCommercial-ShareAlike The muscles of the pelvic floor consist of superficial muscles including the m. bulbospongiosus, m. ischiocavernosus, the perineal muscles and EAS. The deep pelvic floor muscles are the levator ani muscles composed of the puborectalis, pubococcygeus and iliococcygeus. These muscles are attached to the pubic bone, the ischial spine, and the arcus tendinous, a condensation of the obturator fascia in between these areas.17 The puborectalis muscle arises from the symphysis pubis and forms a loop around the recto-anal flexure.19 The puborectalis muscle acts together with the external anal and urethral sphincters to close the urinary and anal openings and contracts the sphincters rapidly in response to an increase of intra-abdominal pressure to prevent incontinence.16
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