Pelvis
From Wikiversity
[edit] Bones and joints of the pelvis
[edit] Pelvic diaphragm
The pelvic diaphragm is the muscular sheet covering the pelvic outlet. It consists of the multi-functional muscle levator ani and the less important coccygeal muscle. Acting together, the muscles of the pelvic diaphragm raise the pelvic floor and contributes in generating intra-abdominal pressure. This causes pressure on abdominal viscera, and is thus important for vomiting, urination and defecation. Also, increased abdominal pressure is used in coughing and forced expiration. Directly, levator ani is cruicial to the voluntary suppression of defecation and urination, as both the rectum and the urethra pass through the muscle. Additionally, it provides support for the uterus in women. Weakness of the levator ani can cause problems such as incontinence and prolapse of the rectum or uterus of women, and exercises of the pelvic diaphragm is a recognized treatment option in managing urinary incontinence (particulary in stress incontinence) in women.
Levator ani (S4) The muscle is symmetrical with two attachments anteriomedially and posteriorly, and has three parts:
- M. pubococcygeus : Stretches between the symphysis pubis and the coccygeus, touching the borders of uterus and rectum. Pubococcygeus constitutes the main body of the levator ani.
- M. puborectalis: An U-shaped muscular sling that passes posteriorly to the anorectal junction, causing an anterior pull on the rectum. This creates a sharp anorectal angle (perineal flexure), which is important for maintaining fecal continence. Thus, during defecation, straightening of the flexure by relaxation of the puborectal muscle must occur.
- M. iliococcygeus is the lowest lying part of the levator ani, and it covers the posterior part of the pelvic outlet, stretching from the obturator fascia to the mid-portion of the coccygeus. This part is often small and not very important.
- M. coccyceus (S4/S5)
Forms a small part of the posterior pelvic diaphragm, and stretches for the ischial spine to the inferior medial sacrum.
