Pelvic diaphragm (Diaphragma pelvis)
The pelvic diaphragm is a foundational structure that forms the floor of the lesser pelvis cavity. This anatomical complex consists of paired muscle structures reliably covered by dense fasciae.
The diaphragm is based on the following muscles:
- Levator ani muscle — m. levator ani. This is a complex structure that includes 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 region of the lesser pelvic outlet. It is a musculo-fascial plate traversed by essential pathways of the urinary and reproductive systems: the urethra, and additionally the vagina in females.
The muscular composition of the urogenital diaphragm includes:
- Deep transverse perineal muscle — m. transversus perinei profundus.
- External urethral sphincter — m. sphincter urethrae.
The fascial anatomy here also has a two-layered structure. The superior and inferior fasciae of the urogenital diaphragm are distinguished. The inferior fascia has a specific name — the perineal membrane (membrana perinei). It is precisely in the space between these two fascial layers that the muscles themselves lie, along with the blood vessels and nerve trunks supplying them.
Functions, blood supply, and innervation
Both diaphragms work as a single functional mechanism. Their joint contraction and tone ensure several critically important tasks:
- Organ fixation — reliable support of the pelvic organs in the correct anatomical position.
- Sphincteric function — control over the retention of pelvic organ contents.
- Pressure resistance — creating resistance to constantly changing intra-abdominal pressure.
- Participation in physiological acts — the muscles are actively involved in defecation, urination, and in women, in the biomechanics of labor.
Trophics and control: Branches of the internal pudendal artery (a. pudenda interna) are responsible for the blood supply to this entire complex. Innervation is provided by the pudendal nerve (n. pudendus) and other branches originating from the sacral plexus.
Briefly: answers to topical questions
What structures pass through the pelvic diaphragm?
The rectum, as well as the urethra and vagina, pass through the pelvic diaphragm.
- Rectum — is the main passing structure in the anal region.
- Urethra and vagina — organs passing through the urogenital hiatus, which is embraced by the medial bundles of the pubococcygeus muscle (m. pubococcygeus).
Which muscles form the superficial layer of the urogenital triangle?
The superficial layer of the urogenital region is formed by three paired muscles.
- Ischiocavernosus muscle (m. ischiocavernosus) — appears as a narrow muscle strip.
- Bulbospongiosus muscle (m. bulbospongiosus) — has an elongated oval shape and surrounds the vaginal opening.
- Superficial transverse perineal muscle (m. transversus perinei superficialis) — a thin, inconstant muscle plate near the posterior margin of the urogenital diaphragm.
What is located in the space between the superior and inferior fasciae of the urogenital diaphragm?
Muscles, vessels, and nerves are located in the space between the superior and inferior fasciae of the urogenital diaphragm. The deep perineal space lies between these fasciae.
It contains:
- Deep transverse perineal muscle (m. transversus perinei profundus) — a paired narrow muscle; its bundles enclose the membranous part of the urethra, forming a sphincter.
Class and exam questions
Where exactly is the urogenital diaphragm located?
It is located in the anterior part of the lesser pelvic outlet, complementing the pelvic diaphragm anteriorly.
What parts does the m. levator ani consist of?
It includes the pubococcygeus (m. pubococcygeus), puborectalis (m. puborectalis), and iliococcygeus (m. iliococcygeus) muscles.
What structures pierce the urogenital diaphragm?
It is pierced by the urethra, and in women, the vagina also passes through it.
What else to study on this topic
- Detailed structure of pelvic fasciae and their derivatives
- Topography of the branches of the internal pudendal artery (a. pudenda interna)
- Course and branching of the pudendal nerve (n. pudendus) in the lesser pelvis cavity
- Biomechanics of the pelvic floor during increased intra-abdominal pressure
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