Pelvic Diaphragm (Diaphragma pelvis)
The pelvic diaphragm forms the foundational base that creates the floor of the pelvic cavity. This anatomical complex consists of paired muscular structures firmly invested by dense fasciae.
The foundation of the diaphragm is composed of the following muscles:
- Levator ani muscle — m. levator ani. This is a complex structure comprising three portions: the pubococcygeus muscle (m. pubococcygeus), the puborectalis muscle (m. puborectalis), and the iliococcygeus muscle (m. iliococcygeus).
- Coccygeus muscle — m. coccygeus.
The muscle layer is protected on both sides by fascial layers. It is covered superiorly by the superior fascia of the pelvic diaphragm (fascia diaphragmatis pelvis superior) and inferiorly by the inferior fascia of the pelvic diaphragm (fascia diaphragmatis pelvis inferior).
Urogenital Diaphragm (Diaphragma urogenitale)
Unlike the pelvic diaphragm, the urogenital diaphragm is located strictly in the anterior part of the pelvic outlet. It is a musculo-fascial plate traversed by critical pathways of the urinary and reproductive systems: the urethra, and additionally the vagina in females.
The muscular components of the urogenital diaphragm include:
- Deep transverse perineal muscle — m. transversus perinei profundus.
- External urethral sphincter — m. sphincter urethrae.
The fascial anatomy here also has a two-layered structure, consisting of superior and inferior fasciae of the urogenital diaphragm. The inferior fascia has a specific designation — the perineal membrane (membrana perinei). The muscles themselves, along with their supplying blood vessels and nerve trunks, lie within the space between these two fascial layers.
Functions, Blood Supply, and Innervation
Both diaphragms work as a unified functional mechanism. Their coordinated contraction and tone provide several critical tasks:
- Organ support — reliable maintenance of pelvic organs in their correct anatomical position.
- Sphincteric function — control over the retention of pelvic organ contents.
- Resistance to pressure — creating resistance against constantly fluctuating intra-abdominal pressure.
- Participation in physiological acts — the muscles are actively involved in defecation, urination, and, in females, the biomechanics of childbirth.
Trophic supply and control: Branches of the internal pudendal artery (a. pudenda interna) supply the blood to this entire complex. Innervation is provided by the pudendal nerve (n. pudendus) and other branches originating from the sacral plexus.