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Attachments, innervation and functions of the muscles of the pelvic floor.
Did you get your workout in today? Crunch those biceps. Get some squats going. What about your pelvic floor? That’s right. I said pelvic floor. Did you know that you could work out those muscles too? Considering that they are the muscles that help you hold onto when you're bursting for the loo, they're pretty worth knowing about. Let’s have a look at what these muscles are and then we'll give you some tips on how to work them out.
Welcome to our tutorial on the muscles of the pelvic floor.
So before we get started, let me give you a quick overview of what we'll cover today. We’ll begin by chatting through what the pelvic floor actually is including its functions. We’ll then move on to reviewing the bones of the pelvis specifically focusing on the features the pelvic floor muscles attached to. Next, we'll look at the floor of the pelvis, identifying its muscles. We’ll then continue to look at some other muscles in the area that are closely related to the pelvic floor including the muscles of the pelvic walls, the muscles of the deep perineal pouch as well as some muscles of the superficial perineal pouch, and finally, a muscle of the anal triangle. Lastly, we'll have a look at how to exercise your pelvic floor muscles before we finish off.
Are you ready? Let’s get to it.
So what is this structure that we're learning about and what is it for? In both of these images, we can see a part of the pelvic floor highlighted in green. On the left, an image of the female pelvis, and on the right, an image of the male pelvis. In both images, we're looking at the pelvis from a right lateral view.
The pelvic floor – also known as the pelvic diaphragm – is an important structure with many functions including providing support for the pelvic organs. We can see this nicely in our images. In both sexes, it provides support for the bladder and the intestines while in females, it also supports the uterus. Additionally, the pelvic floor helps maintain optimal intra-abdominal pressure and is involved in urinary and fecal continence in both sexes.
Okay, so let's get to identifying some of the structures.
First up – a review of the bones of the pelvis. The pelvis as a whole consists of several bones that we'll look at shortly. It’s also known as the pelvic girdle and connects the axial skeleton to the lower limbs. In the midline posteriorly is the sacrum. The sacrum is a fusion of five sacral vertebrae and is attached on either side to the hip bones. Inferior to the sacrum is the most inferior part of the vertebral column – the coccyx. Later on, we'll see how some muscles of the pelvic floor attach to this structure.
Now each hip bone is actually made up of three bones that unite at the acetabulum forming the socket for the hip joint. First is the largest one highlighted now, the ilium; the inferior portion of the hip bone is the ischium, and finally, the anterior portion is the pubis. We’ll be using this image throughout the tutorial, so let's make sure we know what bony structures we can see.
This is the pelvis and the pelvic floor from a superior view, the posterior aspect is at the top of your screen, and the anterior aspect is at the bottom. So, posteriorly, in the midline, is the sacrum. On either side of the sacrum is an ilium. Anteriorly, we can see the two pubic bones. From this view, we can't see much of the ischium, but we can see a bony projection of the ischium called the ischial spine on each side.
This is another image we're going to get very familiar with today. We’re now looking at the pelvis and the pelvic floor from an inferior view. Nevertheless, the posterior aspect is at the top and the anterior aspect is at the bottom. Again, we can see the sacrum posteriorly in the midline. Projecting inferiorly from the sacrum, we can now see the coccyx. On either side of the sacrum, we can see the ilia again, and anteriorly, we have the pubic bones. The ischium is much clearer from this inferior view with the ischial spines projecting here. The other main features of the ischia that we can see are their ischial tuberosities – these large bony features projecting out towards you.
Alright, ready to get to the muscles? Let’s start by looking at the muscles of the pelvic floor.
The pelvic floor is made up of the levator ani muscle, which is a combination of three muscles – the puborectalis, the pubococcygeus, and the iliococcygeus. The pelvic floor also includes another muscle called the coccygeus muscle. We can see in this image that these muscles really fill that inferior portion of the pelvis where they can provide support to the pelvic organs. So let's have a look at each of these muscles in turn.
First up, we can see the entire levator ani muscle highlighted in green. Remember, it consists of three muscles which more or less blend into each other – the puborectalis, the pubococcygeus, and the iliococcygeus.
The first part of the levator ani we'll look at is the puborectalis. This muscle, highlighted in green, is named after its attachments and relations. Pubo- referring to the pubic bone and -rectalis relating to the rectum. The puborectalis originates from the posterior surface of the bodies of the pubic bones. It then extends from its point of origin to form a U-shape sling around the rectum at the anorectal junction. This is pretty different from a lot of skeletal muscle attachments, where insertions are usually to bones. By encircling the anorectal junction, the puborectalis maintains fecal continence. When this muscle relaxes, the angle between the rectum and the anus increases which allows for defecation to occur.
You may have noticed that the puborectalis has two holes in it. The more posteriorly situated hole allows for the passage of the anal canal and is therefore called the anal aperture. But what about the anterior hole? This hole is termed the urogenital hiatus and allows passage of the urethra in both sexes and the vagina in females. In terms of innervation, puborectalis is supplied by the nerve to the levator ani, which arises from the anterior rami of S4, sometimes with a small contribution from S5.
The second component of the levator ani is the pubococcygeus, and nicely done, this muscle is also named after its attachment points. It originates from the bodies of the pubic bones lateral to the origin of the puborectalis. Posteriorly, it inserts at the coccyx and the anococcygeal ligament. Similar to the puborectalis, it is innervated by the nerve to the levator ani, but also receives fibers from the branches of the pudendal nerve such as the inferior rectal or the perineal branches.
The last of the three components of the levator ani is the iliococcygeus muscle. Now this one is a bit deceiving as its name would suggest that it originates from the ilium, but actually the iliococcygeus originates from the ischium – specifically, the ischial spine. It also originates from this structure here - the tendinous arch of the levator ani. Luckily, on the other hand, its insertion point does match its name. Posteriorly, it inserts at the coccyx and the anococcygeal ligament. Like the rest of the levator ani, the iliococcygeus is innervated by the nerve to the levator ani.
The last muscle of the pelvic floor – which is not part of the levator ani – is the muscle we can see highlighted now. This is the coccygeus, which is sometimes called the ischiococcygeus. This muscle originates from the ischial spine and travels posteriorly to insert on the coccyx and inferior portion of the sacrum. From this inferior view, we can see the insertion of the coccygeus, which is highlighted onto the coccyx and the sacrum.
The coccygeus overlies the sacrospinous ligament, which we've just added to the image now. This ligament has similar attachment points – the sacrum and the ischial spine. Sometimes, this muscle and its tendon can fuse together. The coccygeus, as part of the pelvic floor, functions by pulling the coccyx anteriorly after defecation. In other species, its primary function is actually movement of the tail. It is innervated by the nerve to the levator ani, just like the muscles of the levator ani which make up the rest of the pelvic floor.
And before we move on, let me remind you of the functions of the pelvic floor. These muscles work together to provide support for the pelvic organs. Additionally, the pelvic floor helps maintain optimal intra-abdominal pressure and is involved in urinary and fecal continence in both sexes.
There are two additional muscles that aren't technically part of the pelvic floor, but help to form the walls of the pelvic cavity. Let’s take a look at them now.
First up, we'll look at the muscle highlighted now which is the piriformis. Superior and posterior to the coccygeus, this muscle originates medially from the anterior surface of the sacrum and travels out of the pelvis laterally to the greater trochanter of the femur. You can see in this image now how the piriformis makes up the posterolateral wall of the pelvic cavity. This muscle is a lateral rotator and abductor of the thigh, and is innervated by the nerve to the piriformis.
The second muscle which forms part of the anterolateral wall of the pelvic cavity is the obturator internus. Similar to the piriformis, it originates within the pelvis and exits to insert on the femur. Specifically, the obturator internus originates from the posterior surface of the obturator membrane and the surrounding bone and inserts on the greater trochanter of the femur. Just like the piriformis, it is a lateral rotator and abductor of the thigh, but its innervation comes from the nerve to the obturator internus.
Okay, so now that we've covered the muscles of the pelvic floor and the walls, we're going to move inferiorly to identify some more muscles in this region. What we can see here is the levator ani which we know makes up part of the pelvic floor and supports all of these pelvic organs. Inferior to the levator ani, we can see some more muscles. These are the muscles of the perineum. The perineum is a diamond-shaped space inferior to the levator ani between the thighs.
The four points of this diamond are the coccyx posteriorly, the pubic symphysis anteriorly, and the two ischial tuberosities laterally. If we connect the dots along the ischiopubic rami and along the sacrotuberous ligaments, we have our diamond-shaped perineum. The perineum can then be divided into two triangles by drawing a line between the two ischial tuberosities. This forms an anterior urogenital triangle, which contains structures related to the urinary and genital tracts, and a posterior anal triangle, which contains structures related to the intestinal tract.
Within the urogenital triangle, we can further divide the space into two parts. In this image, we're looking at the female pelvis and perineum that has been cut in the coronal plane. This is the bladder sitting within the pelvis which is bounded inferiorly by the pelvic floor. Inferior to the pelvic floor is the perineum and since we're located anteriorly, we're in the urogenital triangle. The dividing line between the two spaces within the urogenital triangle is this structure here, which is the perineal membrane.
The perineal membrane divides the urogenital triangle into two parts - the superior deep perineal pouch and the inferior superficial perineal pouch. So from the pelvic floor as we move inferiorly to the urogenital triangle, we find the deep perineal pouch then the perineal membrane, and inferior to that, the superficial perineal pouch.
Okay, time to get back to the muscles. Let’s start with the muscles in the deep perineal pouch. This pouch contains two muscles – the deep transverse perineal muscle and the external urethral sphincter. First, we'll have a look at the deep transverse perineal muscles which you can now see highlighted in green. We’re looking at the pelvis from that inferior view we've seen a few times so far, but now the muscles of the pelvic floor are covered anteriorly by these perineal muscles.
The deep transverse perineal muscle, which is quite a mouthful, is exactly as its name suggests. It is a deep muscle, but don't worry, there are more muscles that we’ll add superficially soon. It runs transversely from the ramus of each ischium to insert at the walls of the vagina in females, the prostate in males, and the perineal body in both sexes. And, finally, it's a muscle of the perineum.
The deep transverse perineal muscle functions to provide supports to the pelvic floor which, remember, is superior to this muscle. It also stabilizes the perineal body. It is innervated by the deep perineal nerve, which is a branch of the pudendal nerve.
The second muscle of the urogenital diaphragm is the external urethral sphincter, which we can now see highlighted in green towards the anterior aspect of the perineum. This sphincter encircles the membranous portion of the urethra keeping it compressed to maintain urinary continence until it is voluntarily relaxed for micturition, also known as urination. The external urethral sphincter is innervated by the deep perineal nerve.
Now we'll move inferiorly again to have a look at the muscles of the superficial perineal pouch. These muscles are located superficial or inferior to the muscles of the deep perineal pouch we were just looking at. The first lies across the posterior border of the urogenital triangle. This is the superficial transverse perineal muscle. This muscle, similar to its deep counterpart, travels transversely across the perineum. It originates from the ischial tuberosity on each side and inserts medially on the perineal body. This muscle functions to stabilize the perineal body and is innervated by the deep perineal nerve.
Here we can see the first of two erectile muscles that we'll look at today. This is the bulbospongiosus as seen in a female and we'll have a look at the specifics for males shortly. This muscle originates from the perineal body in females. In this coronal section of the female pelvis, we can see the levator ani here making up the pelvic floor. Inferior to that is the deep transverse perineal muscle, which we can see running between the two ischial bones. On either side of the urethral orifice are the vestibular bulbs.
Covering each vestibular bulb is a bulbospongiosus muscle. The vestibular bulbs are the anterior insertion points for the paired bulbospongiosus muscle in females. The muscle runs along them and inserts on the anterior portion. This muscle also inserts at the perineal membrane, the body of the clitoris, and the corpus cavernosum. As for the function, it assists in the erection of the clitoris and the bulb of the vestibule and supports the perineal body. The bulbospongiosus is innervated by the deep perineal nerve.
The bulbospongiosus muscle also exists in males, but is a little bit different. The paired muscles in males unite along the midline at the penile raphe as there is no vaginal opening. They, therefore, originated from the perineal body and the penile raphe in males. In males, the bulbospongiosus runs along the corpus spongiosum and inserts onto its anterior portion. It also inserts at the perineal membrane, the corpus cavernosum, and the fascia of the bulb of the penis. In males, the bulbospongiosus muscle compresses the bulb of the penis during urination and ejaculation, assists in erection of the penis, and supports the perineal body. Just like the bulbospongiosus muscle in females, it is innervated by the deep perineal nerve.
The second of the erectile muscles is the paired ischiocavernosus. This muscle has more similarities between males and females. In both males and females, this muscle originates from the ischial ramus. In females, the ischiocavernosus covers the crus of the clitoris, and like the bulbospongiosus, this muscle assists in erection of the clitoris. In males, the ischiocavernosus covers the crus of the penis which we can see in this coronal section of the male pelvis. Like the bulbospongiosus, this muscle assists in erection of the penis. In both sexes, this muscle is innervated by the deep perineal nerve.
And now, let's move posteriorly to the anal triangle of the perineum to identify our final muscle of this tutorial. This is the external anal sphincter, which as we know, is located in the anal triangle of the perineum. The external anal sphincter originates from the skin and fascia surrounding the anus and is anchored to the perineal body and the anococcygeal ligament. This muscle, as I'm sure you can guess, maintains fecal continence. We can voluntarily relax this muscle to allow for defecation.
This view of the external anal sphincter allows us to see its inferior relationship to the pelvic floor. The external anal sphincter is innervated by the inferior rectal nerve, which is a branch of the pudendal nerve.
Alright, the part that you've all been waiting for – how to exercise your pelvic floor.
The pelvic floor can be weakened in various ways including by childbirth or being overweight. With weak pelvic floor muscles can come urinary and/or fecal incontinence, but Kegel exercises can help improve this. So what are these exercises?
To find these muscles: One, stop urinating midstream. The muscles you used to do this are your pelvic floor muscles. Two, empty your bladder first then lie on your back and tighten your pelvic floor muscles. Three, hold the contraction for five seconds, and four, relax for five seconds. Five, repeat four to five times. Not too harsh of a workout, eh? Hopefully, you won't be sweating too much after this one, and now you're an expert on the pelvic floor muscles.
Before I let you go, let's have a quick review of what we covered today. First, we looked at the pelvic floor itself, also called the pelvic diaphragm, which is made up of the levator ani and the coccygeus. We looked at the three parts of the levator ani identifying each of them. The puborectalis muscle is the first part of the levator ani that we looked at running from the pubic bone and forming a sling around the rectum. We then identified the second part – the pubococcygeus – traveling from the pubic bone all the way to the coccyx posteriorly.
The last part of the levator ani – the iliococcygeus – is the odd one that actually travels from the ischium, rather than the ilium as its name suggests posteriorly to the coccyx. And finally, we identified the coccygeus, which is not part of the levator ani, but still makes up a part of the pelvic floor.
Next up, we looked at the muscles that are part of the pelvic wall. First up was the piriformis, which makes up the posterolateral portion of the wall. Anterolaterally, we found the obturator internus. We then moved to the perineum and started identifying muscles within the deep perineal pouch, which is immediately inferior to the pelvic floor. This broad muscle is the deep transverse perineal muscle, traveling transversely between the two ischial rami. Anteriorly, we found the external urethral sphincter which maintains urinary continence.
The next group of muscles we looked at were in the superficial perineal pouch, which is immediately inferior to the deep perineal pouch. Within this pouch in the urogenital triangle, we identified three pairs of muscles. The first was the superficial transverse perineal muscle, the second was the bulbospongiosus which meets in the midline in males, and finally, the last muscle we looked at was the ischiocavernosus which runs from the ischium and inserts on the crus of the penis or the clitoris.
The final muscle of the tutorial was found posteriorly in the anal triangle. This is where we identified the external anal sphincter which maintains fecal continence.
And that brings us to the end of our tutorial on the muscles of the pelvic floor.
I hope you enjoyed it. Thanks for watching me and happy studying!