Lesson 24: Muscles of the Container

Okay folks, welcome. Lesson 24, muscles of the container. Today we will identify the muscular boundaries of the abdominal pelvic cavity and we'll look at either, or some of them we'll look at all, of the attachments, innervation, and function of muscles of the container and associated structures. So by the end of today's lesson you'll be able to describe the location and organization of muscular boundaries of the abdominal pelvic cavity. identify muscles of the container, and describe the general functions of muscles of the container. For each of these components, so respiratory diaphragm, anterolateral abdominal wall, and pelvic diaphragm, there are also additional learning outcomes. Take some time to just read these thoroughly so you know what's expected of you come assessment time. So let's recall some information. The container, it's formed by a muscular roof, walls, and floor that span from the inferior thoracic aperture to the location of the lesser or true pelvis. So two questions for you. Which osteological structures border the inferior thoracic aperture? I want you to tell me what borders it anteriorly, anterior laterally, posterior laterally, and then posterior. And then where is the lesser or true pelvis located? So specific to an osteological boundary discussed, and then kind of between some of the osteo that we see in this region. Take a second, pause the video, and then I'll reveal the answers. So the inferior thoracic aperture, the most inferior aspect of the thoracic cage. Anteriorly, it is bordered by that xiphoid process. Anteriorlaterally, the costal margin, which if we recall, it's the convergence of the costal cartilage of ribs 8 to 10, converging with rib 7's costal cartilage. Posteriorlaterally, difficult to kind of see here, but those floating ribs, ribs 11 and 12. and then directly posteriorly T12, so that 12th thoracic vertebrae. The lesser or true pelvis is located inferior to the pelvic inlet right here, which means that it is located anterior to the sacrum, medial to the ischium, and posterior to the pubis. Now muscles of the border span or kind of surround the abdominal pelvic cavity, which if you break down that name, it's kind of the convergence of the abdominal cavity and the pelvic cavities. So in this longitudinal section here, we can see the muscular boundary surrounding this great space, the abdominal cavity highlighted in orange, and then the greater and lesser, the pelvis highlighted in these different shades of green. There's no real boundary separating these, right? We use the osteological landmarks to kind of differentiate these spaces, but this entire space is known as the abdominal pelvic cavity. This space is located between the thoracic cavity. So highlighted in purple here, we see the thoracic cavity is located superior to the abdominal pelvic cavity. This space contains the heart and the lungs. We'll really talk about it in Kines 260. And then it's located superior to the perineum, highlighted in blue here. So the perineum containing or the space where our external genitalia lay. This space, this abdominal pelvic cavity, contains most of the gastrointestinal system and the urogenital system. So a lot of the viscera within these systems are involved in many of the processes of the gastrointestinal and urogenital system. The abdominal pelvic cavity, as stated in the slide prior, spans from the inferior thoracic aperture to something that we haven't come across yet, the pelvic outlet. We have the pelvic inlet, so access to the pelvis, and the pelvic outlet, kind of exiting from the pelvic. The pelvic outlet is comprised of the pubic angle, or I should say bordered of the pubic angle, the ischial tuberosities, and the coccyx. So it's kind of this imperfect circle. So that abdominal pelvic cavity spans from the inferior thoracic aperture to the pelvic out limb. But the specific cavities that make up the abdominal pelvic cavity, so abdominal cavity, greater pelvis, lesser pelvis, span varying regions. So the abdominal cavity spans from the inferior thoracic aperture to the pelvic out limb. to the superior anterior aspect of the pelvic girdle right here Here, kind of the more superior aspect of these bones. So think iliac crest, right? Pubic crest, all around here. The greater or false pelvis spans from this superior anterior aspect of the pelvic girdle to the pelvic inlet and then we know that the lesser or true pelvis lays inferior to the pelvic inlet so spanning from the pelvic inlet to the pelvic outlet. The lumbar vertebrae form that posterior border of the abdominal cavity but hopefully we're noting that there's nothing spanning that interior or sorry no osteological structures that span the anterior aspect Now within these regions we have the muscular boundaries of the container. The container is comprised of a muscular roof, the respiratory diaphragm, muscular walls, so the abdominal walls, specifically the posterior abdominal wall located posteriorly, but we're going to ignore that in this class, and then the anterolateral abdominal wall spanning the anterior or the lateral and anterior aspects of this region. And then the pelvic diaphragm kind of comprises that muscular floor of the container, spanning and contained within the lesser pelvis. Now general function of these muscles, they contract. So the respiratory diaphragm contracts, the anterolateral abdominal wall contracts, the pelvic diaphragm contracts, and this contraction increases intra-abdominal pressure, so pressure within the abdomen. This increased pressure has really important functions. One, it's going to aid in expiration. So the increased pressure eventually pushes on the respiratory diaphragm, pushes it upwards to aid in expiration of our air and CO2. This increased pressure also aids in expulsion of fluid, flatus, feces, and fetuses. So the pressure... kind of pressures on the abdominal viscera or the viscera of the urogenital system and gastrointestinal system and it's going to aid with expulsion of fluid such as urine, gas, feces and then it especially helps during childbirth to help guide the fetus out. I want you to think about this region like a pop can. There's a lot of volume in here, a lot of pressure We have the respiratory diaphragm forming the more superior aspect, the pelvic diaphragm, inferior aspect, and the abdominal wall surrounding this region, kind of like the walls of the pop can. And through openings, this pressure is released, and the volume is released, just as we will see with these structures. So let's start with the respiratory diaphragm, the muscular roof of the abdominal pelvic cavity. Again, this is segregating the thoracic cavity and the abdominal pelvic cavity, so it forms that border between the two. It attaches to the osteological boundaries of the inferior thoracic aperture, so syphoid process, costal margin, floating ribs, T12, but it also attaches to the superior lumbar vertebrae. Note that because it's attachment, is to that inferior thoracic aperture. Anteriorly this muscle is much shorter than that posterior aspect which is much longer and you can see that in this anterior lateral view. Shorter anteriorly, longer posteriorly. Here we're looking at a longitudinal section so bisection of an individual we're looking at it from an anterior view we can see the shape of the respiratory diaphragm and specifically the domes. We have a left dome and a right dome. And note that the right dome actually sits much higher or more superior than the left dome. The domes are created due to the presence of the heart. So the heart would be laying right here. You can see that in this image. And that pushes that more central aspect of the respiratory diaphragm to form the left and the right dome. The right dome is more superior. due to the presence of the liver. So we can see that here an accessory organ of the gastrointestinal system present in the upper right quadrant of the abdomen and very large. So again pushing that right dome more superiorly. Now the respiratory diaphragm is comprised of a central tendon and a muscular part. The central tendon we could see here is central and interior kind of looks like a heart. And then surrounding the central tendon in the periphery, we have the muscular part. And this is comprised or subdivided into three other parts. A sternal part, highlighted in green, located directly posterior to the sternum. Costal part, highlighted in blue, costal associated with the ribs. We have it on both the right and the left side. And then the lumbar part, highlighted in yellow, more posterior, associated with the lumbar vertebrae. Here we're looking at a transfer section, again, similar to what we just looked at, but now an inferior view. So again, we're seeing that central tendon located centrally and interiorly, and then the muscular part surrounding it. External part, directly posterior to the sternum. Costal part, more lateral to the central tendon, associated with the ribs. And then the lumbar part, highlighted in yellow here, associated with the lumbar vertebrae. Within or associated with the lumbar part are these crura or crew which are essentially legs or body parts likened to a leg. So you can think of these as the legs of the respiratory diaphragm. We have a right crew and a left crew. These are musculotendinous bands arising from the lumbar vertebrae and anchoring that respiratory diaphragm, specifically the lumbar part of the respiratory diaphragm, to the lumbar vertebrae. I want you to note this space between the left and right crew and then there's another space superior to that within the muscular part of the respiratory diaphragm, specifically the lumbar part. And then most superior in the central tendon, we have another space, another opening right here. These spaces are known as apertures or openings. Again, from superior to inferior, we have the cable opening associated or found within the central tendon, the esophageal hiatus, an opening found in the lumbar part of the respiratory diaphragm, And then this aortic hiatus, this natural opening that's created in between the crura. The cable opening is located at vertebral level T8. So we use vertebral levels in order to, like as surface anatomy landmarks, in order to determine where structures lay internally, especially because we can't always see these structures internally. Traveling through the cable opening is the inferior vena cava, which is this extremely large vein, one of our largest in the body, that brings blood from the lower aspect of the body towards the heart. So it's traveling from the abdomen to the thorax to get to the heart. At vertebral level T10, we can identify the location of the esophageal hiatus. As the name suggesting, the esophagus travels through this opening to get from the thorax to the abdomen to bring that chyme towards the stomach. And then again, at vertebral level T12, we have that aortic hiatus, which is not an opening within the respiratory diaphragm, but rather allows for passage of structures posterior to the diaphragm. again located between that choroa. The structure that travels or kind of the main structure that travels through this hiatus is the aorta which is our largest artery in the entire body. It's bringing blood from the heart to the lower aspect of the body and limbs. We can see these openings from a lateral view. Again this is a longitudinal section, so a bisection. We're looking at it from a lateral view. We can see our vertebrae present posteriorly and the sternum present anteriorly. Vertebral level T8. we can identify the cable opening associated with the central tendon, allowing for the passage of the IBC. At vertebral level T10, we can identify the esophageal hiatus, allowing for the passage of the esophagus into the abdomen. And then at vertebral level T12, we'll note the aorta passing through the aortic hiatus, so passing posterior to the respiratory diaphragm in order to access the abdomen. Now the respiratory diaphragm is a muscle, requires innervation so that it can contract, requires nutrients from arteries. We're going to be concerned with the main nerve that innervates it, and then one artery that supplies it. Bilateral structures, meaning we have these structures present on both the left and right side, so it's important to be specific. Arising in the region of the neck and traveling vertically through the thorax in order to reach the diaphragm, we see the left phrenic nerve in yellow here, and the left pericardiacal phrenic artery bringing blood to this muscle. Same on the right side. Again, arising from the neck, traveling vertically through the thorax or the thoracic cavity, to get to the diaphragm, the right phrenic nerve, and the right pericardiacal phrenic artery. Anytime you see a structure with phrenic in it, it means it's associated with the diaphragm. Phrenic is of or relating to the diaphragm. I want you to know the spinal nerve contributions to the phrenic nerve. We're going to discuss more about this when we touch on the brachial plexus, but specific spinal nerves contribute to formation of the phrenic nerve. C3, C4, and C5. You could remember this by C3, 4, 5 keeps the diaphragm alive. When the heart and lungs are missing in the laboratory setting, you can identify these structures as they again travel vertically. towards the diaphragm. But if the heart and lungs are present, then we want to look for the phrenic nerve and pericardiacophrenic laying lateral or on the lateral aspects of the heart, traveling anterior or in front of the vessels arising from the heart. Now the respiratory diaphragm is the primary muscle of respiration. So it's innervated, it contracts. When it contracts, the left and right dome descend or flatten. This increases the vertical dimension of the thoracic cavity. So right here, increasing the vertical dimension of the thoracic cage. This gives more space for the lungs to expand, allowing inspired air to fill the lungs. Well, how does this impact intra-abdominal pressure? If we are descending, if the respiratory diaphragm is descending, then it's increasing the pressure, that intra-abdominal pressure within this region. Eventually, this intra-abdominal pressure gets to a point where it's so increased, it's going to push back at the diaphragm and push the diaphragm superiorly. This results in forced expiration. How does this impact the apertures and the structures that are traveling through the respiratory diaphragm? to get to and from the thorax and abdomen. While here we're looking at a superior view of a transverse section, we can see the cable opening associated or found within that central tendon and the IBC present within. The esophageal hiatus with the esophagus traveling through it. And then we see the aorta present here. When the respiratory diaphragm contracts and flattens, It actually, the central tendon gets pulled, which widens the cable opening. Well, the IVC adheres to this opening. So as it widens, the IVC also widens or dilates. This actually facilitates blood flow back to the heart because it provides more space for the blood to flow from the abdomen to the superior structure. How does it impact the esophagus? Well, the muscular part. of the respiratory diaphragm is what's contracting. So when it contracts, it actually constricts or closes the esophageal hiatus, which constricts the esophagus. This is a common site of food impaction. So when people tell you not to talk while you're eating, because talking requires air and inspiration and expiration, it's because of this contraction of the respiratory diaphragm. So don't talk while you eat because it can. close up that esophagus or constrict the esophagus and cause food impaction. May have happened to you before where you actually feel that pain kind of just inferior to your sternum, inferior and posterior. Well, it's due to this constriction right here. Contraction of the diaphragm does not impact the aorta. Why is this? Well, hopefully you said because the aorta doesn't travel through the diaphragm. It actually travels posterior to the diaphragm through that aortic hiatus. So contraction of this muscle is not going to impact this great artery, which is a good thing because this artery is bringing blood supply to our lower half of the body, including those lower limbs. So we don't want to reduce blood flow to that region. So inferior to our muscular roof of the abdominal pelvic cavity, we encounter the muscular wall. And again, there is a posterior aspect to this wall, but we're ignoring that within this course. And we're focusing on the anterolateral abdominal wall. These muscles and this space spans between the thoracic cage and the anterolateral aspect of the pelvic girdle, so the hip bones and the pubic symphysis. This anterolateral abdominal wall is actually comprised of six layers, from superficial to deep. The skin, subcutaneous tissue, so fat and superficial fascia, muscles and their aponeuroses, as well as deep fascia that surrounds them, transversalis fascia, extraperitoneal fat, and most deep, the parietal peritoneum, which is a structure we'll discuss with the gastrointestinal system in Kines 260. of concern with us today, the muscles, as well as the transversalis fascia that lays deep to the muscles. Notice the fiber direction of each of these muscles. Extremely different. The most superficial muscle, external oblique, its fibers arise or start at a more superior and lateral aspect and then obliquely travel to a more medial and inferior aspect. Internal oblique, at least that more superior part of it, The fibers start more laterally and inferiorly and obliquely travel in a medial and superior direction. Transversus abdominis, as the name suggests, these fibers travel in a transverse plane, so extremely horizontal. And you can note these fibers are completely perpendicular to the fiber direction of rectus abdominis. At about the midclavicular line, so midclavicular line, midway through the clavicle, if we followed that inferiorly, we would note that these muscles become aponeurotic. So aponeuroses are just a sheet of kind of white fibrous tissue or connective tissue that takes the place of a tendon in these really flat muscles since they have such a wide area of attachment. So we'll note that the external oblique at the mid-clavicular level, it becomes aponeurotic as it travels towards the median plane. The internal oblique. At the midclavicular line, it becomes aponeurotic as it progresses towards the medium plane. Transversus abdominis, I apologize for the noise of my cat in the background, but transversus abdominis, again at the midclavicular line, becomes aponeurotic as it progresses towards the medium plane. In this image, rectus abdominis has been removed, so we can see the aponeurosis of transversus abdominis as it spans towards that midline. Now the aponeurosis of these flat muscles can form very specific structures that we're concerned with. The aponeuroses of all three muscles on either side of the body converge to form this suture or seam known as the linea alba. And the linea alba spans from the xiphoid process to the pubic symphysis. In some individuals, we can see the linea alba from a surface anatomy perspective, spanning from the xiphoid process to about the umbilicus or the belly button. The aponeuroses also form this rectus sheath, the sheath that encloses the vertical muscles, specifically rectus abdominis and pyramidalis and neurovascular structures present within. We're going to discuss specifically how these aponeuroses contribute to formation of this structure. The aponeurosis of external oblique specifically. forms the inguinal ligament and it's formed due to the folding of the external oblique aponeurosis. This spans from the anterior superior iliac spine to the pubic crest and serves as a flexor retinaculum, so a retaining band that retains structures when they produce flexion. Think back to compartments of the The thigh lesson. There's a muscle that travels deep to the inguinal ligament in order to get to the anterior compartment of the thigh. Iliosois. So the flexor retinaculum, the inguinal ligament, retains iliosois in place during movements of flexion of the hip joint. So the rectus sheath. Strong, incomplete fibrous compartment contains rectus abdominis, pyramidalis if it's present, and neurovascular structures. It spans from the xiphoid process to the pubic crest of the pubis bone. Incomplete because it doesn't fully surround the entirety of these vertical muscles, and we'll discuss that. It's important to note the location of the umbilicus or the belly button because a third of the way from the umbilicus to the pubic bone we have this transition and difference in the formation of the rectus sheath so let's look at that here from the xiphoid process to about this imaginary line here so third of the distance from the umbilicus to the pubic crest the anterior or sorry the rectus sheath surrounds the vertical muscles both anteriorly and posteriorly. So the aponeuroses of external oblique, internal oblique, and transversus abdominis are contributing to either or both the anterior and posterior walls. So I want you to think about a little like Ziploc bag for instance and the rectus abdominis muscle being contained and fully surrounded by the anterior and the posterior wall. But inferior to this line, there is no posterior wall of the rectus sheath present. The aponeuroses of external oblique, internal oblique, and transversus abdominis are only contributing to this anterior wall of the rectus sheath. So I want you to think about inferior to this line, we have a little bit of a blanket surrounding rectus abdominis, so tucking in the rectus abdominis muscle. So how do these muscles contribute to the walls? Again, we're highlighting the xiphoid process, the pubic crest, because we know the rectus sheath spans this region. We're noting the umbilicus, and then about a third of the way from the umbilicus to the pubic crest, we have this line demarcating the transition and formation. So the external oblique contributes to the anterior wall of the rectus sheath only. Both. superior to this line and inferior to this line. In this image, external oblique is removed. The internal oblique contributes to both the anterior and posterior wall of the rectus sheath superior to this line, but again, only an anterior wall present here. So the internal oblique is contributing to the anterior wall inferior to this line. Transversus abdominis, we're seeing its fibers here. Superior to this line, transversus abdominis aponeurosis only contributes to the posterior wall. And then inferior to this line, like the other flat muscles, the aponeurosis of transversus abdominis contributes to the anterior wall of the rectus sheath. This is more easily visualized with cross sections. So here we have a cross section of the anterolateral abdominal wall superior, so above the transition, and then we have cross section of the AL wall below the transition or inferior to that line right there. Rectus abdominis present more medially, and then we see our flat muscles present laterally. We can follow external oblique. and it's aponeurosis as it solely contributes to the anterior wall above that line again even below the line we're seeing external oblique as its aponeurosis travels and forms the anterior wall above this transition we see internal oblique and we can follow its aponeurosis it bifurcates it splits contributing to formation of both the anterior and the posterior wall of the rectus sheath however below the transition we can follow the aponeurosis of internal oblique as it only contributes to the anterior wall deepest muscle deepest flat muscle we see transversus abdominis follow its aponeurosis only contributing to the posterior wall above the transition But below that line, we can follow the aponeurosis of transversus abdominis as it contributes to the anterior wall. Deep to our flat muscles, we identify the transversalis fascia. So transversalis fascia, located posterior to the posterior wall, or I should say deep to the posterior wall of the rectus sheath. But below that transition, that posterior wall doesn't exist. So transversus fascia is lining, directly lining, that posterior aspect of rectus abdominis in the absence of that sheath. So we can identify that here. This is a longitudinal section, right, a bisection, or sorry, not a bisection, but a longitudinal section throughout the frontal plane. Imagine we are sitting within the abdominal pelvic cavity, and we're looking at that anterolateral abdominal wall in front of us. So we're actually looking at the deep part of this wall. We can see transversus abdominis, right? We could identify that with certainty due to its muscle fiber direction. Above that line we see its aponeurosis contributing to the posterior wall, the posterior wall of the rectus sheath. Above this line, it's superficial to the transversalis fascia and the transversalis fascia would lay deep to it. However, below the line the posterior wall of the rectus sheath no longer exists. So it's been removed here but we can see transversalis fascia directly lining that rectus abdominis. Internally this transition is demarcated by the arcuate line, right? So superior to the arcuate line, posterior wall of the rectus sheath present, transversalis fascia lining or deep to that posterior wall. Inferior to the arcuate line, no posterior wall present, that transversalis fascia directly lining the posterior aspect of rectus abdominis. And then we'll note that even deeper to transversalis fascia, we have that parietal peritoneum, right? The deepest structure of the AL wall, but again, to be discussed next semester. So when you're in the lab... Look at the abdominal, anterolateral abdominal wall from a superficial perspective, and then look at it from a deep perspective, because you'll be able to see this arcuate line that marks this transition. Now contain within that rectus sheath, as we've discussed, rectus abdominis. rectus. We've seen a rectus femoris before, parallel to the midline. So vertical fibers traveling in a sagittal plane perpendicular to our transversus abdominis muscle. Rectus abdominis is anchored to the rectus sheath via these tendinous intersections. Typically, individuals have three on either side. Sometimes there's four, sometimes there's two, it can be variable. When someone is flexing, these tendinous intersections actually cause bulging of the muscles between them, which gives us this appearance of the eight-pack, the six-pack, the two-pack, whatever you may have. And that may be dictated, again, by the presence and number of tendinous intersections you have. So general function of the anterolateral abdominal wall. Well, recall, there's no osteology present anteriorly. So these muscles have an important role in supporting and protecting the abdominal viscera. So viscera of the GI system and the urogenital system. These muscles can contract to maintain or increase the intra-abdominal pressure. Once that intra-abdominal pressure is increased, well, the diaphragm can be elevated to for forced expiration. This intra-abdominal pressure can aid in compressing the abdominal viscera, which helps with expulsion, right, of urine, of gas. VCs of fetuses during childbirth. It also can compress on the viscera to facilitate blood flow, so to direct that blood flow superiorly, specifically when discussing the IVC, to return that blood to the heart. These muscles can relax to accommodate movement of the diaphragm, since that diaphragm is going to compress, or sorry, descend during inspiration, and also movement of the abdominal viscera. right during their kind of processes for metabolism of food and and just mechanical digestion of food it's also going to aid in moving the trunk so rectus abdominis note it's in the sagittal it's kind of attachments are in the sagittal plane this is going to aid in flexion of the trunk so bringing the trunk forward which is technically indirect flexion of the lumbar vertebrae so where's our ex Our intrinsic back muscles complete extension of the vertebral column. Rectus abdominis is going to aid with flexion, along with iliopsoas, right, when the thighs are stabilized. External oblique and internal oblique also contribute to lateral flexion of the trunk, right, to the left, to the right, and rotation of the trunk as well. Inferior to the location of the anterolateral abdominal wall, we now encounter the muscular floor of the abdominal pelvic cavity, the pelvic diaphragm. The pelvic diaphragm is going to be found within the region of the lesser true pelvis, and it closes that pelvic outlet to separate the lesser and true pelvis and the abdominal pelvic cavity from the perineum. You can see in this longitudinal section that this pelvic diaphragm kind of drapes like a hammock. So I want you to think about it like a hammock, spanning from the left hip bone and sacrum to the right hip bone and sacrum. This group of muscles, the pelvic diaphragm, specifically attaches to the sacrum and the coccyx posteriorly, the ischial spine, present here and here. the pubis present anteriorly, and then what's known as the tendinous arch of obturator fascia. So this thickening of fascia or connective tissue present on the muscle in this region. The pelvic diaphragm is comprised of two muscles, and one of those muscles is subdivided into three parts. So highlighted in blue, located most posteriorly. We identify coccygeus or ischio coccygeus. It originates from the ischial spine, inserts to the sacrum and coccyx. Then anterior and medial to this muscle, we encounter levator ani. And levator ani is comprised of three parts. Directly anterior to coccygeus, we identify iliococcygeus. This muscle originating from the ischial spine and that tendinous arch of the obturator fascia and then tapering to insert to the coccyx. Anterior and medial to iliococcygeus, highlighted in purple, we can identify pubococcygeus. Name telling you its attachments, the pubis, the tendinous arch, and then inserting on the coccyx. Highlighted in green, we have puborectalis. Now this muscle is forming a sling around the rectum, so it's known as the puborectal sling. It originates from the pubis and inserts on the pubis. Medial to this muscle, we can note the presence of the urogenital hiatus. So we've come across other hiatuses, right? The aortic hiatus, The esophageal hiatus, the adductor hiatus, these are just natural openings. And the urogenital hiatus specifically allows for the passage of urogenital viscera, urethra, vagina. More posterior to the urogenital hiatus, we have the rectal hiatus. And this is a space for the rectum or anal canal. Again, this muscle directly is associated with the rectum because it forms that Pupil rectal sling. When pubococcygeus and puborectalis are no longer present, you can kind of better see the shape. of coxigeous and ileocoxigeous. And I want you to think of them as two triangles, but oriented differently. So coxigeous is tapered more laterally, and then is more broad in its insertion site on the sacrum and coccyx. Whereas ileocoxigeous is more broad laterally on its origin site and tapers as it reaches the coccyx. So just another visual to help you differentiate these two muscles. So what's the main function of the pelvic diaphragm? Well, this muscle, this muscle group, is pretty well always in a state of sustained contraction. It sustains its contraction in order to support the abdominal pelvic viscera that is present superior to it and to maintain urinary and fecal continence. Specifically, think about the puborectalis muscle, right? We can see it in this image here, attaching to the pubis, surrounding the rectum. It kind of changes the orientation. It angles the rectum in order to ensure fecal continence. This group of muscle can also actively contract. Now, it actively contracts primarily to increase support of the abdominal pelvic. viscera located superior to it during moments of increased intra-abdominal pressure. I think coughing, sneezing, lifting something really heavy, that's all going to increase the intra-abdominal pressure. So we want to have a strong pelvic floor in order to ensure we're maintaining that urinary and fecal continence. But with this contraction, it also increases intra-abdominal pressure. So it's kind of like a loop. essentially. And again, that intra-abdominal pressure increase can aid in expulsion. Now, these muscles eventually, must eventually relax in order to allow for urinary, or urination rather, and defecation. Here's a summary for you. And again, a few slides for you to practice identifying these structures prior to entering the laboratory.

For each of these components, so respiratory diaphragm, anterolateral abdominal wall, and pelvic diaphragm, there are also additional learning outcomes. Take some time to just read these thoroughly so you know what's expected of you come assessment time. So let's recall some information.

The container, it's formed by a muscular roof, walls, and floor that span from the inferior thoracic aperture to the location of the lesser or true pelvis. So two questions for you. Which osteological structures border the inferior thoracic aperture?

I want you to tell me what borders it anteriorly, anterior laterally, posterior laterally, and then posterior. And then where is the lesser or true pelvis located? So specific to an osteological boundary discussed, and then kind of between some of the osteo that we see in this region.

Take a second, pause the video, and then I'll reveal the answers. So the inferior thoracic aperture, the most inferior aspect of the thoracic cage. Anteriorly, it is bordered by that xiphoid process. Anteriorlaterally, the costal margin, which if we recall, it's the convergence of the costal cartilage of ribs 8 to 10, converging with rib 7's costal cartilage. Posteriorlaterally, difficult to kind of see here, but those floating ribs, ribs 11 and 12. and then directly posteriorly T12, so that 12th thoracic vertebrae.

The lesser or true pelvis is located inferior to the pelvic inlet right here, which means that it is located anterior to the sacrum, medial to the ischium, and posterior to the pubis. Now muscles of the border span or kind of surround the abdominal pelvic cavity, which if you break down that name, it's kind of the convergence of the abdominal cavity and the pelvic cavities. So in this longitudinal section here, we can see the muscular boundary surrounding this great space, the abdominal cavity highlighted in orange, and then the greater and lesser, the pelvis highlighted in these different shades of green.

There's no real boundary separating these, right? We use the osteological landmarks to kind of differentiate these spaces, but this entire space is known as the abdominal pelvic cavity. This space is located between the thoracic cavity.

So highlighted in purple here, we see the thoracic cavity is located superior to the abdominal pelvic cavity. This space contains the heart and the lungs. We'll really talk about it in Kines 260. And then it's located superior to the perineum, highlighted in blue here.

So the perineum containing or the space where our external genitalia lay. This space, this abdominal pelvic cavity, contains most of the gastrointestinal system and the urogenital system. So a lot of the viscera within these systems are involved in many of the processes of the gastrointestinal and urogenital system. The abdominal pelvic cavity, as stated in the slide prior, spans from the inferior thoracic aperture to something that we haven't come across yet, the pelvic outlet. We have the pelvic inlet, so access to the pelvis, and the pelvic outlet, kind of exiting from the pelvic.

The pelvic outlet is comprised of the pubic angle, or I should say bordered of the pubic angle, the ischial tuberosities, and the coccyx. So it's kind of this imperfect circle. So that abdominal pelvic cavity spans from the inferior thoracic aperture to the pelvic out limb.

But the specific cavities that make up the abdominal pelvic cavity, so abdominal cavity, greater pelvis, lesser pelvis, span varying regions. So the abdominal cavity spans from the inferior thoracic aperture to the pelvic out limb. to the superior anterior aspect of the pelvic girdle right here Here, kind of the more superior aspect of these bones.

So think iliac crest, right? Pubic crest, all around here. The greater or false pelvis spans from this superior anterior aspect of the pelvic girdle to the pelvic inlet and then we know that the lesser or true pelvis lays inferior to the pelvic inlet so spanning from the pelvic inlet to the pelvic outlet. The lumbar vertebrae form that posterior border of the abdominal cavity but hopefully we're noting that there's nothing spanning that interior or sorry no osteological structures that span the anterior aspect Now within these regions we have the muscular boundaries of the container. The container is comprised of a muscular roof, the respiratory diaphragm, muscular walls, so the abdominal walls, specifically the posterior abdominal wall located posteriorly, but we're going to ignore that in this class, and then the anterolateral abdominal wall spanning the anterior or the lateral and anterior aspects of this region.

And then the pelvic diaphragm kind of comprises that muscular floor of the container, spanning and contained within the lesser pelvis. Now general function of these muscles, they contract. So the respiratory diaphragm contracts, the anterolateral abdominal wall contracts, the pelvic diaphragm contracts, and this contraction increases intra-abdominal pressure, so pressure within the abdomen. This increased pressure has really important functions. One, it's going to aid in expiration.

So the increased pressure eventually pushes on the respiratory diaphragm, pushes it upwards to aid in expiration of our air and CO2. This increased pressure also aids in expulsion of fluid, flatus, feces, and fetuses. So the pressure... kind of pressures on the abdominal viscera or the viscera of the urogenital system and gastrointestinal system and it's going to aid with expulsion of fluid such as urine, gas, feces and then it especially helps during childbirth to help guide the fetus out. I want you to think about this region like a pop can.

There's a lot of volume in here, a lot of pressure We have the respiratory diaphragm forming the more superior aspect, the pelvic diaphragm, inferior aspect, and the abdominal wall surrounding this region, kind of like the walls of the pop can. And through openings, this pressure is released, and the volume is released, just as we will see with these structures. So let's start with the respiratory diaphragm, the muscular roof of the abdominal pelvic cavity. Again, this is segregating the thoracic cavity and the abdominal pelvic cavity, so it forms that border between the two.

It attaches to the osteological boundaries of the inferior thoracic aperture, so syphoid process, costal margin, floating ribs, T12, but it also attaches to the superior lumbar vertebrae. Note that because it's attachment, is to that inferior thoracic aperture. Anteriorly this muscle is much shorter than that posterior aspect which is much longer and you can see that in this anterior lateral view.

Shorter anteriorly, longer posteriorly. Here we're looking at a longitudinal section so bisection of an individual we're looking at it from an anterior view we can see the shape of the respiratory diaphragm and specifically the domes. We have a left dome and a right dome.

And note that the right dome actually sits much higher or more superior than the left dome. The domes are created due to the presence of the heart. So the heart would be laying right here.

You can see that in this image. And that pushes that more central aspect of the respiratory diaphragm to form the left and the right dome. The right dome is more superior. due to the presence of the liver. So we can see that here an accessory organ of the gastrointestinal system present in the upper right quadrant of the abdomen and very large.

So again pushing that right dome more superiorly. Now the respiratory diaphragm is comprised of a central tendon and a muscular part. The central tendon we could see here is central and interior kind of looks like a heart. And then surrounding the central tendon in the periphery, we have the muscular part.

And this is comprised or subdivided into three other parts. A sternal part, highlighted in green, located directly posterior to the sternum. Costal part, highlighted in blue, costal associated with the ribs. We have it on both the right and the left side. And then the lumbar part, highlighted in yellow, more posterior, associated with the lumbar vertebrae.

Here we're looking at a transfer section, again, similar to what we just looked at, but now an inferior view. So again, we're seeing that central tendon located centrally and interiorly, and then the muscular part surrounding it. External part, directly posterior to the sternum.

Costal part, more lateral to the central tendon, associated with the ribs. And then the lumbar part, highlighted in yellow here, associated with the lumbar vertebrae. Within or associated with the lumbar part are these crura or crew which are essentially legs or body parts likened to a leg.

So you can think of these as the legs of the respiratory diaphragm. We have a right crew and a left crew. These are musculotendinous bands arising from the lumbar vertebrae and anchoring that respiratory diaphragm, specifically the lumbar part of the respiratory diaphragm, to the lumbar vertebrae. I want you to note this space between the left and right crew and then there's another space superior to that within the muscular part of the respiratory diaphragm, specifically the lumbar part. And then most superior in the central tendon, we have another space, another opening right here.

These spaces are known as apertures or openings. Again, from superior to inferior, we have the cable opening associated or found within the central tendon, the esophageal hiatus, an opening found in the lumbar part of the respiratory diaphragm, And then this aortic hiatus, this natural opening that's created in between the crura. The cable opening is located at vertebral level T8. So we use vertebral levels in order to, like as surface anatomy landmarks, in order to determine where structures lay internally, especially because we can't always see these structures internally.

Traveling through the cable opening is the inferior vena cava, which is this extremely large vein, one of our largest in the body, that brings blood from the lower aspect of the body towards the heart. So it's traveling from the abdomen to the thorax to get to the heart. At vertebral level T10, we can identify the location of the esophageal hiatus. As the name suggesting, the esophagus travels through this opening to get from the thorax to the abdomen to bring that chyme towards the stomach. And then again, at vertebral level T12, we have that aortic hiatus, which is not an opening within the respiratory diaphragm, but rather allows for passage of structures posterior to the diaphragm.

again located between that choroa. The structure that travels or kind of the main structure that travels through this hiatus is the aorta which is our largest artery in the entire body. It's bringing blood from the heart to the lower aspect of the body and limbs. We can see these openings from a lateral view. Again this is a longitudinal section, so a bisection.

We're looking at it from a lateral view. We can see our vertebrae present posteriorly and the sternum present anteriorly. Vertebral level T8. we can identify the cable opening associated with the central tendon, allowing for the passage of the IBC. At vertebral level T10, we can identify the esophageal hiatus, allowing for the passage of the esophagus into the abdomen.

And then at vertebral level T12, we'll note the aorta passing through the aortic hiatus, so passing posterior to the respiratory diaphragm in order to access the abdomen. Now the respiratory diaphragm is a muscle, requires innervation so that it can contract, requires nutrients from arteries. We're going to be concerned with the main nerve that innervates it, and then one artery that supplies it. Bilateral structures, meaning we have these structures present on both the left and right side, so it's important to be specific.

Arising in the region of the neck and traveling vertically through the thorax in order to reach the diaphragm, we see the left phrenic nerve in yellow here, and the left pericardiacal phrenic artery bringing blood to this muscle. Same on the right side. Again, arising from the neck, traveling vertically through the thorax or the thoracic cavity, to get to the diaphragm, the right phrenic nerve, and the right pericardiacal phrenic artery.

Anytime you see a structure with phrenic in it, it means it's associated with the diaphragm. Phrenic is of or relating to the diaphragm. I want you to know the spinal nerve contributions to the phrenic nerve. We're going to discuss more about this when we touch on the brachial plexus, but specific spinal nerves contribute to formation of the phrenic nerve.

C3, C4, and C5. You could remember this by C3, 4, 5 keeps the diaphragm alive. When the heart and lungs are missing in the laboratory setting, you can identify these structures as they again travel vertically. towards the diaphragm.

But if the heart and lungs are present, then we want to look for the phrenic nerve and pericardiacophrenic laying lateral or on the lateral aspects of the heart, traveling anterior or in front of the vessels arising from the heart. Now the respiratory diaphragm is the primary muscle of respiration. So it's innervated, it contracts.

When it contracts, the left and right dome descend or flatten. This increases the vertical dimension of the thoracic cavity. So right here, increasing the vertical dimension of the thoracic cage. This gives more space for the lungs to expand, allowing inspired air to fill the lungs. Well, how does this impact intra-abdominal pressure?

If we are descending, if the respiratory diaphragm is descending, then it's increasing the pressure, that intra-abdominal pressure within this region. Eventually, this intra-abdominal pressure gets to a point where it's so increased, it's going to push back at the diaphragm and push the diaphragm superiorly. This results in forced expiration.

How does this impact the apertures and the structures that are traveling through the respiratory diaphragm? to get to and from the thorax and abdomen. While here we're looking at a superior view of a transverse section, we can see the cable opening associated or found within that central tendon and the IBC present within.

The esophageal hiatus with the esophagus traveling through it. And then we see the aorta present here. When the respiratory diaphragm contracts and flattens, It actually, the central tendon gets pulled, which widens the cable opening.

Well, the IVC adheres to this opening. So as it widens, the IVC also widens or dilates. This actually facilitates blood flow back to the heart because it provides more space for the blood to flow from the abdomen to the superior structure. How does it impact the esophagus?

Well, the muscular part. of the respiratory diaphragm is what's contracting. So when it contracts, it actually constricts or closes the esophageal hiatus, which constricts the esophagus. This is a common site of food impaction. So when people tell you not to talk while you're eating, because talking requires air and inspiration and expiration, it's because of this contraction of the respiratory diaphragm.

So don't talk while you eat because it can. close up that esophagus or constrict the esophagus and cause food impaction. May have happened to you before where you actually feel that pain kind of just inferior to your sternum, inferior and posterior.

Well, it's due to this constriction right here. Contraction of the diaphragm does not impact the aorta. Why is this?

Well, hopefully you said because the aorta doesn't travel through the diaphragm. It actually travels posterior to the diaphragm through that aortic hiatus. So contraction of this muscle is not going to impact this great artery, which is a good thing because this artery is bringing blood supply to our lower half of the body, including those lower limbs. So we don't want to reduce blood flow to that region.

So inferior to our muscular roof of the abdominal pelvic cavity, we encounter the muscular wall. And again, there is a posterior aspect to this wall, but we're ignoring that within this course. And we're focusing on the anterolateral abdominal wall. These muscles and this space spans between the thoracic cage and the anterolateral aspect of the pelvic girdle, so the hip bones and the pubic symphysis.

This anterolateral abdominal wall is actually comprised of six layers, from superficial to deep. The skin, subcutaneous tissue, so fat and superficial fascia, muscles and their aponeuroses, as well as deep fascia that surrounds them, transversalis fascia, extraperitoneal fat, and most deep, the parietal peritoneum, which is a structure we'll discuss with the gastrointestinal system in Kines 260. of concern with us today, the muscles, as well as the transversalis fascia that lays deep to the muscles. Notice the fiber direction of each of these muscles.

Extremely different. The most superficial muscle, external oblique, its fibers arise or start at a more superior and lateral aspect and then obliquely travel to a more medial and inferior aspect. Internal oblique, at least that more superior part of it, The fibers start more laterally and inferiorly and obliquely travel in a medial and superior direction.

Transversus abdominis, as the name suggests, these fibers travel in a transverse plane, so extremely horizontal. And you can note these fibers are completely perpendicular to the fiber direction of rectus abdominis. At about the midclavicular line, so midclavicular line, midway through the clavicle, if we followed that inferiorly, we would note that these muscles become aponeurotic.

So aponeuroses are just a sheet of kind of white fibrous tissue or connective tissue that takes the place of a tendon in these really flat muscles since they have such a wide area of attachment. So we'll note that the external oblique at the mid-clavicular level, it becomes aponeurotic as it travels towards the median plane. The internal oblique.

At the midclavicular line, it becomes aponeurotic as it progresses towards the medium plane. Transversus abdominis, I apologize for the noise of my cat in the background, but transversus abdominis, again at the midclavicular line, becomes aponeurotic as it progresses towards the medium plane. In this image, rectus abdominis has been removed, so we can see the aponeurosis of transversus abdominis as it spans towards that midline. Now the aponeurosis of these flat muscles can form very specific structures that we're concerned with. The aponeuroses of all three muscles on either side of the body converge to form this suture or seam known as the linea alba.

And the linea alba spans from the xiphoid process to the pubic symphysis. In some individuals, we can see the linea alba from a surface anatomy perspective, spanning from the xiphoid process to about the umbilicus or the belly button. The aponeuroses also form this rectus sheath, the sheath that encloses the vertical muscles, specifically rectus abdominis and pyramidalis and neurovascular structures present within.

We're going to discuss specifically how these aponeuroses contribute to formation of this structure. The aponeurosis of external oblique specifically. forms the inguinal ligament and it's formed due to the folding of the external oblique aponeurosis. This spans from the anterior superior iliac spine to the pubic crest and serves as a flexor retinaculum, so a retaining band that retains structures when they produce flexion. Think back to compartments of the The thigh lesson.

There's a muscle that travels deep to the inguinal ligament in order to get to the anterior compartment of the thigh. Iliosois. So the flexor retinaculum, the inguinal ligament, retains iliosois in place during movements of flexion of the hip joint.

So the rectus sheath. Strong, incomplete fibrous compartment contains rectus abdominis, pyramidalis if it's present, and neurovascular structures. It spans from the xiphoid process to the pubic crest of the pubis bone. Incomplete because it doesn't fully surround the entirety of these vertical muscles, and we'll discuss that.

It's important to note the location of the umbilicus or the belly button because a third of the way from the umbilicus to the pubic bone we have this transition and difference in the formation of the rectus sheath so let's look at that here from the xiphoid process to about this imaginary line here so third of the distance from the umbilicus to the pubic crest the anterior or sorry the rectus sheath surrounds the vertical muscles both anteriorly and posteriorly. So the aponeuroses of external oblique, internal oblique, and transversus abdominis are contributing to either or both the anterior and posterior walls. So I want you to think about a little like Ziploc bag for instance and the rectus abdominis muscle being contained and fully surrounded by the anterior and the posterior wall. But inferior to this line, there is no posterior wall of the rectus sheath present. The aponeuroses of external oblique, internal oblique, and transversus abdominis are only contributing to this anterior wall of the rectus sheath.

So I want you to think about inferior to this line, we have a little bit of a blanket surrounding rectus abdominis, so tucking in the rectus abdominis muscle. So how do these muscles contribute to the walls? Again, we're highlighting the xiphoid process, the pubic crest, because we know the rectus sheath spans this region. We're noting the umbilicus, and then about a third of the way from the umbilicus to the pubic crest, we have this line demarcating the transition and formation.

So the external oblique contributes to the anterior wall of the rectus sheath only. Both. superior to this line and inferior to this line.

In this image, external oblique is removed. The internal oblique contributes to both the anterior and posterior wall of the rectus sheath superior to this line, but again, only an anterior wall present here. So the internal oblique is contributing to the anterior wall inferior to this line.

Transversus abdominis, we're seeing its fibers here. Superior to this line, transversus abdominis aponeurosis only contributes to the posterior wall. And then inferior to this line, like the other flat muscles, the aponeurosis of transversus abdominis contributes to the anterior wall of the rectus sheath. This is more easily visualized with cross sections.

So here we have a cross section of the anterolateral abdominal wall superior, so above the transition, and then we have cross section of the AL wall below the transition or inferior to that line right there. Rectus abdominis present more medially, and then we see our flat muscles present laterally. We can follow external oblique.

and it's aponeurosis as it solely contributes to the anterior wall above that line again even below the line we're seeing external oblique as its aponeurosis travels and forms the anterior wall above this transition we see internal oblique and we can follow its aponeurosis it bifurcates it splits contributing to formation of both the anterior and the posterior wall of the rectus sheath however below the transition we can follow the aponeurosis of internal oblique as it only contributes to the anterior wall deepest muscle deepest flat muscle we see transversus abdominis follow its aponeurosis only contributing to the posterior wall above the transition But below that line, we can follow the aponeurosis of transversus abdominis as it contributes to the anterior wall. Deep to our flat muscles, we identify the transversalis fascia. So transversalis fascia, located posterior to the posterior wall, or I should say deep to the posterior wall of the rectus sheath.

But below that transition, that posterior wall doesn't exist. So transversus fascia is lining, directly lining, that posterior aspect of rectus abdominis in the absence of that sheath. So we can identify that here. This is a longitudinal section, right, a bisection, or sorry, not a bisection, but a longitudinal section throughout the frontal plane. Imagine we are sitting within the abdominal pelvic cavity, and we're looking at that anterolateral abdominal wall in front of us.

So we're actually looking at the deep part of this wall. We can see transversus abdominis, right? We could identify that with certainty due to its muscle fiber direction. Above that line we see its aponeurosis contributing to the posterior wall, the posterior wall of the rectus sheath.

Above this line, it's superficial to the transversalis fascia and the transversalis fascia would lay deep to it. However, below the line the posterior wall of the rectus sheath no longer exists. So it's been removed here but we can see transversalis fascia directly lining that rectus abdominis. Internally this transition is demarcated by the arcuate line, right?

So superior to the arcuate line, posterior wall of the rectus sheath present, transversalis fascia lining or deep to that posterior wall. Inferior to the arcuate line, no posterior wall present, that transversalis fascia directly lining the posterior aspect of rectus abdominis. And then we'll note that even deeper to transversalis fascia, we have that parietal peritoneum, right? The deepest structure of the AL wall, but again, to be discussed next semester.

So when you're in the lab... Look at the abdominal, anterolateral abdominal wall from a superficial perspective, and then look at it from a deep perspective, because you'll be able to see this arcuate line that marks this transition. Now contain within that rectus sheath, as we've discussed, rectus abdominis.

rectus. We've seen a rectus femoris before, parallel to the midline. So vertical fibers traveling in a sagittal plane perpendicular to our transversus abdominis muscle. Rectus abdominis is anchored to the rectus sheath via these tendinous intersections. Typically, individuals have three on either side.

Sometimes there's four, sometimes there's two, it can be variable. When someone is flexing, these tendinous intersections actually cause bulging of the muscles between them, which gives us this appearance of the eight-pack, the six-pack, the two-pack, whatever you may have. And that may be dictated, again, by the presence and number of tendinous intersections you have. So general function of the anterolateral abdominal wall. Well, recall, there's no osteology present anteriorly.

So these muscles have an important role in supporting and protecting the abdominal viscera. So viscera of the GI system and the urogenital system. These muscles can contract to maintain or increase the intra-abdominal pressure.

Once that intra-abdominal pressure is increased, well, the diaphragm can be elevated to for forced expiration. This intra-abdominal pressure can aid in compressing the abdominal viscera, which helps with expulsion, right, of urine, of gas. VCs of fetuses during childbirth. It also can compress on the viscera to facilitate blood flow, so to direct that blood flow superiorly, specifically when discussing the IVC, to return that blood to the heart.

These muscles can relax to accommodate movement of the diaphragm, since that diaphragm is going to compress, or sorry, descend during inspiration, and also movement of the abdominal viscera. right during their kind of processes for metabolism of food and and just mechanical digestion of food it's also going to aid in moving the trunk so rectus abdominis note it's in the sagittal it's kind of attachments are in the sagittal plane this is going to aid in flexion of the trunk so bringing the trunk forward which is technically indirect flexion of the lumbar vertebrae so where's our ex Our intrinsic back muscles complete extension of the vertebral column. Rectus abdominis is going to aid with flexion, along with iliopsoas, right, when the thighs are stabilized.

External oblique and internal oblique also contribute to lateral flexion of the trunk, right, to the left, to the right, and rotation of the trunk as well. Inferior to the location of the anterolateral abdominal wall, we now encounter the muscular floor of the abdominal pelvic cavity, the pelvic diaphragm. The pelvic diaphragm is going to be found within the region of the lesser true pelvis, and it closes that pelvic outlet to separate the lesser and true pelvis and the abdominal pelvic cavity from the perineum.

You can see in this longitudinal section that this pelvic diaphragm kind of drapes like a hammock. So I want you to think about it like a hammock, spanning from the left hip bone and sacrum to the right hip bone and sacrum. This group of muscles, the pelvic diaphragm, specifically attaches to the sacrum and the coccyx posteriorly, the ischial spine, present here and here.

the pubis present anteriorly, and then what's known as the tendinous arch of obturator fascia. So this thickening of fascia or connective tissue present on the muscle in this region. The pelvic diaphragm is comprised of two muscles, and one of those muscles is subdivided into three parts.

So highlighted in blue, located most posteriorly. We identify coccygeus or ischio coccygeus. It originates from the ischial spine, inserts to the sacrum and coccyx. Then anterior and medial to this muscle, we encounter levator ani.

And levator ani is comprised of three parts. Directly anterior to coccygeus, we identify iliococcygeus. This muscle originating from the ischial spine and that tendinous arch of the obturator fascia and then tapering to insert to the coccyx.

Anterior and medial to iliococcygeus, highlighted in purple, we can identify pubococcygeus. Name telling you its attachments, the pubis, the tendinous arch, and then inserting on the coccyx. Highlighted in green, we have puborectalis. Now this muscle is forming a sling around the rectum, so it's known as the puborectal sling.

It originates from the pubis and inserts on the pubis. Medial to this muscle, we can note the presence of the urogenital hiatus. So we've come across other hiatuses, right? The aortic hiatus, The esophageal hiatus, the adductor hiatus, these are just natural openings.

And the urogenital hiatus specifically allows for the passage of urogenital viscera, urethra, vagina. More posterior to the urogenital hiatus, we have the rectal hiatus. And this is a space for the rectum or anal canal.

Again, this muscle directly is associated with the rectum because it forms that Pupil rectal sling. When pubococcygeus and puborectalis are no longer present, you can kind of better see the shape. of coxigeous and ileocoxigeous. And I want you to think of them as two triangles, but oriented differently. So coxigeous is tapered more laterally, and then is more broad in its insertion site on the sacrum and coccyx.

Whereas ileocoxigeous is more broad laterally on its origin site and tapers as it reaches the coccyx. So just another visual to help you differentiate these two muscles. So what's the main function of the pelvic diaphragm?

Well, this muscle, this muscle group, is pretty well always in a state of sustained contraction. It sustains its contraction in order to support the abdominal pelvic viscera that is present superior to it and to maintain urinary and fecal continence. Specifically, think about the puborectalis muscle, right? We can see it in this image here, attaching to the pubis, surrounding the rectum. It kind of changes the orientation.

It angles the rectum in order to ensure fecal continence. This group of muscle can also actively contract. Now, it actively contracts primarily to increase support of the abdominal pelvic. viscera located superior to it during moments of increased intra-abdominal pressure. I think coughing, sneezing, lifting something really heavy, that's all going to increase the intra-abdominal pressure.

So we want to have a strong pelvic floor in order to ensure we're maintaining that urinary and fecal continence. But with this contraction, it also increases intra-abdominal pressure. So it's kind of like a loop.

essentially. And again, that intra-abdominal pressure increase can aid in expulsion. Now, these muscles eventually, must eventually relax in order to allow for urinary, or urination rather, and defecation. Here's a summary for you.

And again, a few slides for you to practice identifying these structures prior to entering the laboratory.

Transcript for:Lesson 24: Muscles of the Container

Transcript for:
Lesson 24: Muscles of the Container