15.13:
Muscles of the Pelvic Floor and Perineum
The pelvic diaphragm marks the inferior margin of the abdominopelvic cavity. It is formed by the paired levator ani and coccygeus muscles, which attach to the internal walls of the true pelvis.
While the pelvic diaphragm is penetrated by the anal canal and urethra in both sexes, females have the vagina as an additional opening.
The levator ani is the largest three-part muscle of the pelvic floor, comprising the pubococcygeus, the puborectalis, and the iliococcygeus muscles.
It primarily supports pelvic organs, such as the bladder, and acts as a sphincter at the anorectal junction, urethra, and vagina.
Under the pelvic diaphragm lies the diamond-shaped region called the perineum.
It is divided into an anterior urogenital triangle, housing the external genitals, and a posterior anal triangle, which contains the anus.
The urogenital triangle includes the superficial transverse perineal, bulbospongiosus, and ischiocavernosus muscles of the external genitalia.
The anal triangle has the anal canal surrounded by the external anal sphincter. Its other prominent muscles include the obturator internus and the inferior region of the levator ani.
15.13:
Muscles of the Pelvic Floor and Perineum
The muscles of the pelvic floor and perineum are crucial for supporting the pelvic organs, controlling continence, and aiding in sexual function, childbirth, and core stability. They are typically divided into the superficial perineal layer and the deep pelvic floor layer.
Perineal Layer
The perineum is a diamond-shaped area below the pelvic diaphragm, divided into an anterior urogenital triangle that contains the external genitals and a posterior anal triangle housing the anus. The urogenital triangle consists of the superficial transverse perineal, bulbospongiosus, and ischiocavernosus muscles. The bulbospongiosus muscle surrounds the vaginal or penile areas to assist in sexual functions and support. The ischiocavernosus muscle helps maintain an erection in both males and females by compressing the outflow veins of the erectile tissues. Additionally, the superficial transverse perineal muscles support the pelvic organs and aid in maintaining continence.
Conversely, the posterior anal triangle contains the anus and is characterized by the presence of the external anal sphincter, which is essential for voluntary control over defecation. Surrounding this area are significant muscles like the obturator internus, which supports the pelvic organs and aids in lateral rotation of the thigh, and the inferior part of the levator ani from the pelvic diaphragm above, providing additional support and stability to the pelvic floor.
Pelvic Floor
Deeper within the pelvic floor lies a group of muscles that form a sling or hammock-like structure supporting the pelvic organs. The levator ani, a significant component of this layer, includes muscles such as the pubococcygeus, puborectalis, and iliococcygeus. These muscles are crucial for supporting the pelvic organs, maintaining continence, and facilitating childbirth by stretching and expanding as needed. The coccygeus muscle, extending from the ischial spine to the lower end of the sacrum and coccyx, complements the levator ani by providing additional support and stability.