Origins, insertions, innervation and functions of the muscles of the pelvic floor.
Muscles of the pelvic floor - Human Anatomy | Kenhub
Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, we're going to be talking about the muscles of the pelvic floor. So, what we’re going to be doing here on this tutorial is exploring some of these muscles that you see here on this image. We’re looking now at the cranial view of your pelvis – the bony pelvis here as you can see – and the different muscles that we’re going to be talking about that define what we know of the or as the pelvic floor.
And if we’ll move on to these images here, you have on the left side an image of the female pelvis where we highlighted here in green the muscles – cut here as you can see – the muscles of the pelvic floor. You can also see here the different muscles of the pelvic floor but this time on a male pelvis. We can see here cuts of the male pelvis and also of the female pelvis and we’re looking at it from a lateral view, specifically a right lateral view.
Now, what we’re going to see here is that the pelvic floor, also known as pelvic diaphragm, is an important structure providing many things including support for the different pelvic organs as you can see here on these images. So, it provides support, for example, to the bladder – as you can see here on these two images – and also the intestines. Additionally, in women, you can see that it provides support to this organ here which is then the uterus.
Now, the pelvic floor muscles are the layer – as you can see here highlighted in green – that supports the pelvic organs and spans the bottom of the pelvis. Now, during birthing, the pelvic floor will be facilitating movement of the fetus towards the pelvic girdle by resisting the descent of the presenting part and which causes the fetus to then rotate forwards and, therefore, results in a majority of fetuses being born head first. Now, the pelvic floor is also helping in maintaining the optimal intra-abdominal pressure, so a few functions here listed of or associated to the pelvic floor.
We’re now ready to move on and talk about all these muscles that I, that we’re, supposed to cover here on this tutorial and right now on this image on the right side we’re looking at the inferior view of the pelvis with the different muscles that we’re going to be covering. This is to say that the muscles of the pelvic floor can be divided into the following groups: the pelvic diaphragm, there is also a group called the urogenital diaphragm, and the sphincters and erectile muscles of the urogenital tract. On the following slides, we’re going to go over these different groups and the specific muscles, learn all the origins, insertions, innervations and functions associated to these muscles.
And let’s start with the very first group here on this list, the pelvic diaphragm. This group includes the levator ani which is a combination of 3 muscles: the puborectalis, the pubococcygeus and the iliococcygeus. And the pelvic diaphragm also includes another muscle known as the coccygeus. And in order of this list, let’s start off with the very first muscle that you see here highlighted in green, the puborectalis.
And as I mentioned before, this muscle is part of the levator ani group. In terms of origin points, this muscle is going to be originating lateral from the pubic symphysis, the superior fascia of the urogenital diaphragm. As for the insertion point of the puborectalis, we usually learn that muscles are attaching to different parts of bones and also ligaments. In this case, the puborectalis will be inserting at or encircling the rectum, anorectal junction to be specific, which causes then a ventral band between the rectum and also the anal canal. Partially, it is interwoven with the external anal sphincter. In terms of the innervation of the puborectalis, it is going to be supplied by different fibers from S3 to S4 and also the levator ani nerve.
We’re going to move on and talk about the different functions associated to the puborectalis and the main function that we need to remember every time we talk about the puborectalis is that this muscle is going to be able to inhibit defecation. So, relaxation will be increasing the angle between the rectum and anus allowing then defecation and conjugation with relaxation of the internal and external sphincters.
We’re ready to move on to another muscle that you see here highlighted in green from a cranial view of the pelvis, we’re looking now at the pubococcygeus. This muscle is a hammock-like muscle that is found in both sexes and that forms the floor of the pelvic cavity and supporting the pelvic organs as well as I mentioned before and it is part of the levator ani group of muscles. When it comes to the origin points for the pubococcygeus, it runs from the pubic bone lateral to the origin of the puborectalis muscle as you can clearly see here on this image, just laterally to this muscle that we talked about. As for the insertion point of the pubococcygeus, the tendinous center of the perineum and the anococcygeal body will be serving as the insertion points for the pubococcygeus. Not to forget that also the tailbone, also known as the coccyx, is going to serve as an insertion point for the pubococcygeus. And, in men, the medial muscle fibers are partially connected to the prostate. Now, as for the innervation of the pubococcygeus, this muscle is going to receive fibers from S3 to S4. The main functions of the pubococcygeus muscle, they are to then control urine flow and to also contract during orgasm.
Next muscle that we’re going to be highlighting here on this image is the iliococcygeus. This muscle is also part of the levator ani group of muscles. When it comes to the origin points, the iliococcygeus arises from the inner side of the ischium and also from the posterior part of the tendinous arch of the obturator fascia. The muscle goes all the way then to insert at the coccyx or the tailbone and also the anococcygeal raphe or body. As for the innervation for the iliococcygeus muscle, the pudendal nerve is going to come from the sacral plexus and innervate the iliococcygeus. As for a quick word on the different functions associated to the iliococcygeus, one that is important to remember is that it will be able to lift and also close the anus.
We’re going to move to the last one on the list of the pelvic diaphragm, the coccygeus muscle, seen here highlighted in green from a cranial view of the pelvis. Now, the coccygeus is a muscle of the pelvic floor that is located posterior to the levator ani muscle which you can see here on this image, this is the different muscles that form the levator ani muscle. So, this is the posterior part where you find then the sacrum and you can see here then the coccygeus highlighted in green. This muscle is also found anterior to an important ligament known as the sacrospinous ligament. And as you can see, this muscle is a triangular plane of muscular and tendinous fibers. As for the origin of the coccygeus muscle, it arises from the spine of the ischium which you can see here on this image and also that ligament that I talked about, the sacrospinous ligament.
As for the insertion point for the coccygeus muscle, this muscle is inserted into the margin of the tailbone, the coccyx, and into the side of the lowest piece of then the sacrum and you can see here a bit of this muscle into this bone here, the sacrum. When it comes to the innervation of the coccygeus muscle, this muscle is going to be innervated by sacral nerves S4, S5 or also you can see that in some references, they might mention then S3 to S4. As for the different functions or main function of the coccygeus muscle, this muscle will be pulling the coccyx forward after defecation, closing in then the back portion of the outlet of the pelvis.
The next groups of muscles will be forming then urogenital diaphragm and they include then the deep transverse perineal and the sphincter urethrae. Let’s start off with the very first one that you see here highlighted in green which is the first one on the list, the deep transverse perineal. And the deep transverse perineal muscle lies in the perineum and is a part of the pelvic floor. This muscle will be arising from the inferior ramus of the ischium and also runs to then the median line. Then this muscle goes all the way to insert at the deep transverse perineal muscle of the opposite side as you can see here. So, each muscle is meeting here in the middle to then attach and they are originating here from the ramus of the ischium. As for the innervation of the deep transverse peroneal muscle, this muscle is going to be innervated by the pudendal nerve.
Let’s talk about the different functions associated to this muscle. Now, the function of the deep transverse perineal muscle is to then fixate the central tendon of the perineum and also provides support to the pelvic floor. This involved in expulsion of semen in males and the last drops of urine in both sexes.
The next muscle that we’re going to be seeing here highlighted in green – this really small muscle that you’ll find here – this is known as the external urethral sphincter or the, as we saw listed previously, as the sphincter urethrae. The external sphincter muscle of the urethra will be surrounding the whole length of the membranous portion of the urethra and this is also enclosed in the fasciae of the urogenital diaphragm. As for the origin points for this muscle, it is going to be originating at the junction of the inferior rami of the pubis and also the ischium and the neighboring fasciae. Now for insertion point, we can say that this muscle is going to be inserting at the ischiopubic rami. The external urethral sphincter will be innervated by the deep branch of the perineal nerve. Now, a quick word on the function of the external urethral sphincter, this muscle is going to constrict the urethra maintaining then the urinary continence.
We’re moving on to the last list of muscles which are then considered muscles or sphincters and erectile muscles of the urogenital and intestinal tracts. And the list includes the external anal sphincter, the bulbospongiosus, the ischiocavernosus, and the superficial transverse perineal muscle.
Let’s start off with the very first muscle that you see here highlighted in green, the external anal sphincter. The external anal sphincter is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus. Now, this muscle is around 8 to 10 cm in length approximately from its anterior end to its posterior extremity is about 2.5 cm opposite to the anus. When defecation occurs, the sphincter muscle will be then retracting. For the origin point for the external anal sphincter, the only one that you need to remember is that this muscle is going to be originating from the anococcygeal body, also known as the anococcygeal raphe. As for then the insertion point for the external anal sphincter, the central tendon of perineum will be serving as an insertion point for this muscle.
The next point that we’re going to make here about this muscle is that the innervation is going to come from a branch of the 4th sacral and also twigs from the inferior rectal branch of the pudendal nerve. I’d like a quick word on the different functions associated to the external anal sphincter. Now, the actions associated to this muscle are a bit peculiar. It is always like other muscles, always in the state of tonic contraction and, having no antagonistic muscle, it will be then keeping the anal canal and orifice closed. Voluntarily, it can be put into a condition of greater contraction so as more firmly to occlude the anal aperture and expiratory efforts which are not connected with defecation. Now, taking its fixed point at the coccyx, this muscle will be helping fix the central point of the perineum so that the bulbocavernosus may act from this fixed point.
We’re going to move on to this muscle that you see here now highlighted in green which is known as the bulbospongiosus and is one of the superficial muscles of the perineum. It arises from the central tendon of perineum and from the median raphe in front of it. Now, the fibers of this muscle will be radiating anterolaterally and then lose themselves in the inferior fascia of the urogenital diaphragm. As for the innervation of the bulbospongiosus muscle, in both sexes, it is innervated by the deep/muscular branch of the peroneal nerve which is a branch of the pudendal nerve.
We’re going to move on and talk about the different functions associated to this muscle. In males, it will be contributing to then erection, ejaculation, and feelings of orgasm. In females, this muscle is going to be contributing to clitoral erection and also feelings of orgasm. As it contracts, it can also be involved in closing the vagina.
Now, we’re going to move on and talk about this muscle that you see now highlighted in green, the ischiocavernosus. Now, this is a muscle just below the surface of the perineum. For the origin points, in males, the fleshy fibers will be originating in the inner surface of the tuberosity of the ischium while in females, it will be originating from the ramus of the ischium. In males and in females, we’re also going to see different insertion points. So, in males, it is going to be inserting at the crus of the penis and, in females, it’s going to be attaching to the corpus cavernosum of the clitoris.
The next point we’re going to be talking about the ischiocavernosus is its innervation. This muscle is innervated by the perineal nerve and, as for the different functions associated to the ischiocavernosus, this muscle compresses the crus of the clitoris forcing blood in its sinuses into the distal part of the corpus cavernosum in females. It is also involved in stabilizing the erect penis in males and also flexes the anus. Kegel exercises also known as pelvic floor exercises can help tone the ischiocavernosus muscle.
Next on our list here highlighted in green, we see the superficial transverse perineal muscle. This muscle is a narrow muscular slip which passes more or less transversely across the perineal space anterior to then the anus, as you can clearly see here on this image. As for the origin point, this muscle is going to be arising by tendinous fibers from the inner and forepart of the tuberosity of the ischium which you can clearly see here on this image – this is the tuberosity of the ischium on both sides and see how the muscle is originating from the structures. The muscle goes all the way to then insert into the central tendon of perineum or the perineal body, joining in this way with the muscle of the opposite side, as you can see also here on this image. It also joins the external anal sphincter just behind and with the bulbospongiosus muscle just in front.
Now, the innervation of the superficial transverse perineal muscle is going to be then the perineal nerve. This nerve is going to be responsible for innervating this muscle. We’re moving onto the different functions associated to this muscle. Fixation of the central tendon of the perineum and also supporting of the pelvic floor are the 2 main functions associated to the superficial transverse perineal muscle.
We’re going to move on and talk about a few other neighboring muscles that you’ll find near these muscles that we just talked about and even on these images that we’ve been seeing throughout this tutorial. We’re going to start off with this one that you see here highlighted in green from a cranial view of the pelvis, the obturator internus muscle. Now, this muscle originates at the medial surface of the obturator membrane. Other origin points include the ischium near the membrane and the rim of the pubic bone. As for insertion point, the obturator internus is going to then insert at the medial aspect of the greater trochanter of the femur. The innervation of the obturator internus is carried out by the nerve to then the obturator internus coming from L5, S1, S2 from the sacral plexus. The functions associated to the obturator internus include then laterally rotating the femur with hip extension or external rotation of the femur and also abducts the femur with hip flexion as well as to steady the femoral head in the acetabulum.
The next muscle that you’ll find nearby – this muscle – also seen from a cranial view is known as the piriformis. Now, the piriformis is a muscle in the gluteal region of the lower limb. It is one of the 6 muscles in the lateral rotator group. The piriformis muscle originates from the pelvic or anterior surface of the sacrum. And you can see here on this image a little bit of the origin point at the sacrum, to be more specific, the pelvic surface or the portion of the sacrum facing the pelvis or also known as the anterior part of the sacrum. The muscle goes all the way to then insert at the femur at this part known as the greater trochanter of the femur. As for the innervation of the piriformis muscle, the piriformis is innervated by the nerve to the piriformis coming from L5, S1 and S2 from the sacral plexus. Now, before we finish this tutorial, a quick word on the different functions associated to the piriformis. This muscle will be responsible for laterally rotating the femur with hip extension and also abducts the femur with hip flexion.
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