Muscles of the pelvic floor
The pelvic floor is primarily made up of thick skeletal muscles along with nearby ligaments and their investing fascia. It is a basin-shaped muscular diaphragm that helps to support the visceral contents of the pelvis. The main focus of this article will be the pelvic floor muscles. On that topic, there are several important questions that need to be answered:
- Which muscles make up the pelvic floor?
- What arteries and nerves supply the muscles of the pelvic floor?
- What causes pelvic floor dysfunction?
- What is the best exercise for the pelvic floor?
A variably thick muscular membrane called a diaphragm
Coccygeus and levator ani muscles (iliococcygeus, puborectalis, pubococcygeus)
Pubococcygeus can be further separated into – puboperinealis, puboprostaticus (male), pubovaginalis (female), puboanalis
Mnemonic: Could I Please Peek?
Laterally – attached to the tendinous arch of levator ani
Posterolaterally – attached to the ischial spine
Posteriorly – attached to the caudal sacrum and coccyx
Anteriorly – attached to the posterior surface of the pubis
Midline – fibers form a midline levator raphe
|Branches of the anterior division of the internal iliac artery: inferior vesical, pudendal, inferior gluteal
Pudendal nerve (S2, S3)
Direct branches from S4 (nerve to levator ani)
|Hypaxial division of the sacrococcygeal myotome
Prevents pelvic organ prolapse
Childbirth – supports and guides the presenting fetal part
Helps maintain continence (both urinary and fecal)
Pelvic organ prolapse
These and other questions will be addressed as we discuss the gross anatomy and function of the muscles of the pelvic floor. The piriformis and obturator internus muscles will not be discussed in great detail as they are primarily muscles of the lower limb. The muscles that are up for discussion are those that form the lower limit of the true pelvis and have attachment only to structures within the bony pelvis.
- Gross anatomy
- Blood supply
- Clinical significance
The pelvis marks an important transition point between the thoracoabdominal region and the lower limbs. Not only is it important for walking, but it also houses organs of the urogenital and distal digestive systems and acts as a conduit for arteries, veins, lymphatic vessels, and nerves necessary for daily functioning. The pelvis is a musculoskeletal structure that is made up of hip and sacrococcygeal bones, along with several muscular layers. It is further divided into the greater (false) and lesser (true) pelvis. The false pelvis is the wide-area just above the inlet between the ala of the ilia while the true pelvis is the area between the inlet and the outlet. It has two lateral walls, a posterior wall (sacrococcygeal bones), and a muscular floor.
The lower part of the pelvis is sealed off by a muscular diaphragm and perineal membrane known as the pelvic floor. There are two (males) or three (females) openings that allow passage of the outlet components of the pelvic viscera in the pelvic floor. The muscles of the pelvic floor contribute to maintaining continence and help prevent the contents of the pelvic cavity from falling through its outlet.
The muscles of the pelvic floor are collectively referred to as the levator ani and coccygeus muscles. They form a large sheet of skeletal muscle that is thicker in some areas than in others. The muscles are attached along the inner walls of the true pelvis to a condensed area of the obturator fascia known as the tendinous arch of levator ani muscle. They can be subdivided based on their points of attachment as well as the pelvic organs with which they are associated. Note that the levator ani is made up of the puborectalis, pubococcygeus, and iliococcygeus muscles. The coccygeus (also referred to as ischiococcygeus) is not part of the levator ani.
The pelvic surface of the levator ani is separated from the visceral organs by their associated fascia. The perineal surface functions as the medial and superior walls of the ischioanal fossa and its associated anterior recess respectively. There is loose connective tissue between the posterior border of the muscle and the coccyx. Finally, the outlets of the visceral organs separate the medial border of the two muscles.
Origin: Posterior surface of bodies of pubic bones
Insertion: None (forms 'puborectal sling' posterior to rectum)
Innervation: Nerve to levator ani (S4)
Origin: Posterior surface of bodies of pubic bones (lateral to puborectalis)
Insertion: Anococcygeal ligament, Coccyx, Perineal body and musculature of prostate/vagina
Innervation: Nerve to levator ani (S4); branches via inferior rectal/perineal branches of the pudendal nerve (S2-S4)
Origin: Tendinous arch of the internal obturator fascia, Ischial spine
Insertion: Anococcygeal ligament, Coccyx
Innervation: Nerve to levator ani (S4)
Origin: Ischial spine
Insertion: Inferior end of sacrum, Coccyx
Innervation: Anterior rami of spinal nerves S4-S5
The coccygeus (ischiococcygeus) muscle is sometimes considered as a part of the levator ani complex rather than as a separate muscle. However, this muscle is actually a separate entity that is situated at the most posterosuperior aspect of the muscle complex.
It is a triangular sheet of muscle with its apex inserted on the tip and pelvic surface of the ischial spine and the base is attached to the 5th sacral segment and the lateral margins of the coccyx. The remaining fibers of the muscle converge at the midline. The muscle is anteriorly related to the pelvic surface of the sacrospinous ligament.
The iliococcygeus part of levator ani is anteroinferior to coccygeus muscle and posterosuperior to pubococcygeus. The muscle extends laterally to the tendinous arch of the levator ani. The posterolateral fibers have attachments to the ischial spine (just inferior and anterior to the coccygeus muscle attachment), while the anterolateral fibers attach at the obturator canal. The posterior midline fibers are attached to the lower part of the sacrum and coccyx.
The majority of fibers of iliococcygeus meet with fibers of the contralateral half of the muscle to form a midline raphe. The raphe – a groove where the two halves of the muscle unite – is continuous with the anococcygeal ligament and provides a strong posterior attachment for the pelvic floor.
The pubococcygeus is the intermediate part of the levator ani muscles. The anterior fibers arise from the posterior surface of the pubic arch and travel posteriorly in the horizontal plane. The fibers then decussate to meet with the fibers from the contralateral side, to form a sling around the distal parts of the pelvic organs. Pubococcygeus can be further subdivided based on the structures that the fibers are immediately associated with:
- Puboperinealis - The innermost fibers travel adjacent to the urethra and its associated sphincter as it exits the pelvic floor. In some instances, the muscle is called pubourethralis because it is associated with the proximal half of the urethra and forms part of its sphincter complex
- Puboprostaticus (males) and pubovaginalis (females) - Another group of muscle fibers passes around the inferior part of the prostate (in males) or posterior wall of the vagina (in females).
- Puboanalis - A few fibers cross to the other side and blends with the fibers of the longitudinal rectal muscles and fascia to form the conjoint longitudinal coat of the anal canal.
The puborectalis passes behind the rectum along the levator raphe as a muscular sling curving around the anorectal junction. Collectively, the subdivisions of pubococcygeus and the puborectalis muscle together are referred to as the pubovisceralis.
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The anterior division of the internal iliac artery is responsible for supplying the levator ani group of muscles with oxygenated, nutrient-rich blood. Its three terminal branches – the pudendal, inferior gluteal, and inferior vesical arteries – access and pierce these muscles in order to supply them. Venous drainage is achieved by the similarly named veins.
Learn more about the arterial blood supply and venous drainage of the pelvic floor and pelvis with these study units!
Branches from the sacral plexus contribute to the innervation of the levator ani group of muscles. The pudendal nerve, which originates from the second to fourth sacral segments (S2-S4) directly innervate the pubococcygeus muscle. Direct branches arising from the fourth sacral segment form the nerve to levator ani (S4), which also innervates the pubococcygeus. The remaining coccygeus and iliococcygeus are innervated by direct branches from the fourth and fifth segments (S4 and S5) of the sacral plexus.
Check out these resources to solidify your knowledge about the sacral plexus and innervation of the pelvic floor muscles.
The muscles of the pelvic floor are primarily supportive structures. They help keep the pelvic viscera in place and prevent them from being pushed through the pelvis during strain. It achieves this task by being unconsciously contracted at rest and can be consciously contracted during times of raised intra-abdominal pressure (vomiting, sneezing, coughing, lifting a heavy object, or forced expiration).
Contraction of the levator ani muscles also provides additional occlusion to the outlet segments of the pelvic viscera. In other words, the muscles aid in maintaining both urinary and fecal continence until it is convenient to void. The puborectalis muscle best demonstrates this function. Recall that it is a muscular sling U-shaped muscle that arches around the anorectal junction. When this part of the muscle is contracted, it pulls the anorectal junction anteriorly, forming a 90 degrees angle between the rectum and anus. Therefore fecal matter cannot flow freely from the rectum. In order for micturition (urination) and defecation to occur, the levator ani muscles must be relaxed.
Want to learn more about the muscles of the pelvic floor? With attachments, innervations and functions clearly detailed in handy revision tables, our trunk wall muscle chart has you covered.
The pelvic floor muscles also provide additional support during childbirth to the presenting fetal part – the part closest to the uterine outlet. It holds the fetus in place while the uterine cervix dilates and contracts. It also keeps the presenting part of the fetus in the anteroposterior plane of the pelvic outlet to further support the process of delivery.
Histologically, the majority of the pelvic floor muscles are made up of slow-twitch or type I muscle fibers. The prevalence of type I fibers is important given the function of the pelvic floor muscles outlined above. Recall that type I fibers are ideal for long periods of contraction, while type II fibers are needed for quick response to physiological changes.
The muscles of the pelvic floor can be contracted under voluntary control and are therefore skeletal muscles. This means that these muscle fibers arise from the dermomyotomes of somites and undergo an epithelial to mesenchymal transition. Multiple transformation factors promote the conversion of mesenchymal cells to myoblasts (primitive muscle cells).
Myoblasts are characterized by longer nuclei and cell bodies in comparison to their precursor cells. Some of these myoblasts fuse to form myotubes – multinucleated cylindrical cells. As fusion takes place, myofibrils and other skeletal muscle organelles begin to appear in the cell cytoplasm. As the myoblasts continue to form they migrate away from their myotomes to form non-segmented muscle groups. Those of the pelvic floor arises from the hypaxial division of the sacrococcygeal myotomes.
The role of the pelvic floor is to provide structural support and help maintain continence. Therefore any disorder of these muscles would result in instability of the pelvic organs (prolapse) and incontinence. Pelvic floor disorders are more commonly encountered in females than males. This results from the fact that most of the risk factors (obstetric causes and hormone-related ligament laxity) occur exclusively in females. However, both males and females may experience urinary or fecal incontinence for different reasons. The issue of organ prolapse, however, remains mostly a gynecological problem. One of the most distressing complications of defective pelvic floor musculature is pelvic organ prolapse.
Pelvic organ prolapse
Pelvic organ prolapse is essentially herniation of pelvic viscera through its associated opening. For example, uterine prolapse through the vaginal vault, or rectal prolapse through the anus. The disorder is associated with weakening of the pelvic floor. This weakness can be induced by over-distension of the muscle over time. The risk factors for developing pelvic floor dysfunction and subsequently pelvic organ prolapse can be non-obstetric (chronic coughing, obesity, smoking, ethnicity, age, history of connective tissue disorder) or obstetric (multiparity, prolonged labor, precipitous labor, operative vaginal delivery). An occupational history suggestive of long term heavy lifting may also increase the risk of developing pelvic floor weakness and subsequent organ prolapse.
Women who experience pelvic organ prolapse may experience feeling a mass protruding from the vaginal opening. They may have an anterior wall prolapse associated with a prolapsed bladder (cystocele), which will cause symptoms of urinary retention. They may also have a posterior wall prolapse associated with a bulging of rectal wall (rectocele), which leads to constipation. Others may experience uterine prolapse where the cervix is extending through the vaginal opening. Even women who have had their uterus removed (hysterectomy) may have prolapse of a poorly suspended vaginal vault.
Both men and women may experience rectal prolapse. This is a debilitating condition where either part of the rectal mucosa or the entire rectum can descend through the anus. It is also more prevalent in women than in men. Most of the predisposing risk factors for pelvic organ prolapse also increase the chances of developing rectal prolapse.
The weakening of the pelvic floor muscles can lead to incontinence as well as a pelvic organ or rectal prolapse. There are some exercises that can help improve problems with urine leakage or bowel control. Women are often told during pregnancy or after childbirth to perform Kegel exercises, also known as pelvic floor exercises, to try and prevent urinary incontinence and to help women who have difficulty achieving orgasm following pregnancy.
Kegel exercise instructions
The goal of Kegel exercises is to isolate and train the muscles of the pelvic floor. A good way to isolate these muscles is to attempt stopping the process of urination midstream. The muscles that are activated during this process are the pelvic floor muscles. These are also the muscles used to prevent passing gas (flatus).
Before beginning the exercise, first empty your bladder. Next, lie on your back and tighten the pelvic floor muscles identified earlier. Now hold the contraction for 5 seconds, then relax for 5 seconds. Repeat this process 4 to 5 times, up to 3 times a day. Once you’ve become comfortable holding contraction for 5 seconds, increase the holding time to 10 seconds for each contraction and relaxation.
Avoid activating the abdominal, thigh, or buttocks muscles during this process and ensure you’re breathing freely. Take note not to use Kegel exercises to start and stop your urine stream on a regular basis. Performing these exercises while emptying your bladder can actually weaken the muscles, which can result in incomplete bladder emptying and resultant urinary tract infections.
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