 In this video, I will identify select muscles and use anatomical terminology to describe their location and action. I'll start here looking at the muscles of facial expression found on the anterior cephalic region. There is a muscle overlying the frontal bone known as the frontal belly of occipitofrontalis. So occipitofrontalis is a muscle covering the superior surface of the cranium that has two muscle bellies or two muscular compartments. There's an occipital belly found on the posterior overlying the occipital bone and a frontal belly found on the anterior overlying the frontal bone. However, occipitofrontalis is a bit of a mouthful and so I prefer just to drop the first part of that word and stick with frontalis. So frontalis is a synonym for occipitofrontalis and so frontalis is this muscle that we can see overlying the frontal bone on the anterior of the cranium. So next we'll move down to orbicularis oculi. So orbicularis means that this is a circular shaped muscle where the fibers of the muscles are surrounding the eye surrounding the ocular region. So here we can see the circular shape of orbicularis oculi and the action of this muscle is to close the eyelids. So while frontalis elevates the eyebrows orbicularis oculi closes the eyelids. So we can see there's a similarly named muscle surrounding the mouth. We have orbicularis aureus. So orbicularis aureus is a circular shaped muscle similar to orbicularis oculi. It has that circular shape. But orbicularis aureus is found surrounding the aural region and the action of orbicularis aureus is to close the lips. So now we have another view where I've labeled the zygomaticus muscles. So there are zygomaticus major and zygomaticus minor. So zygomaticus major is a little larger and more lateral compared to zygomaticus minor. So here I'm highlighting the zygomaticus major. So zygomaticus major and zygomaticus minor both contribute to the action of elevating the corner of the mouth. What we commonly refer to as smiling. So zygomaticus major is a major muscle of facial expression helping contribute to this action of smiling. But zygomaticus minor is also contributing to elevating the upper lip and contributing to that facial expression of smiling. So these muscles are named after the zygomatic bone. So the zygomaticus muscles connect from the zygomatic bone down to the lips where they can contribute to that action of elevating the corners of the mouth, elevating the angles of the mouth to produce a smile. So here's another view with zygomaticus major highlighted. Now we can see the origin of zygomaticus major is on the zygomatic bone. Whereas the insertion, the mobile location that when this muscle contracts will move to produce the action is on the corner of the mouth, on the skin at the corner of the mouth. So that the action of this muscle is smiling or to elevate the corner of the mouth. Now this slide is showing us the muscles of mastication, meaning the muscles that we use to move the mandible for chewing. The major muscle that I want to emphasize in this class is the masseter. So here you can see the masseter, a large muscle of mastication, it's named after its action. So the action is to elevate the mandible, to raise the mandible superiorly. The location of the masseter is found superficially in the buccal region. The masseter attaches to the zygomatic bone and the mandible. And so its insertion again is the part that moves. So the mandible is the insertion for the masseter, whereas the zygomatic bone doesn't move, the zygomatic bone is the origin for the masseter. And the action of this muscle is to elevate the mandible, raise the mandible superiorly, which is the action you'd need to bite on something. We commonly say you bite down on something, but in reality what we do is we elevate the mandible to take a bite. So we can see there's also several more muscles that contribute to mastication. The temporalis is a superficial muscle found on the lateral aspect of the cranium. And the teregoid muscles are deeper muscles of mastication, connecting from the sphenoid bone to the mandible. So the actions of elevation and depression for the mandible correspond to opening and closing the jaw. When we depress the mandible, we open the jaw and we could relax the masseter in order to enable depression of the mandible. And when we contract the masseter, that causes elevation of the mandible to close the jaw. The jaw can also be moved anteriorly and posteriorly. So the word for moving anteriorly is protraction and the movement posterior, that's the opposite of protraction, is known as retraction. Here again we can see the masseter, a major muscle of mastication that is chewing. So the masseter has its origin from the zygomatic bone and inserts on the mandible to enable this action of elevation of the mandible. Now this view is showing us the superficial muscles on the anterior of the abdomen. There are external abdominal obliques. So the external oblique is an abdominal muscle that's found on the lateral aspects of the abdomen. And it's called an oblique muscle because the muscle fibers of the oblique muscle are running diagonally. So they're not running straight up and down the long axis of the body, but they're also not running at 90 degrees perpendicular to the long axis of the body. They run roughly 45 degrees obliquely relative to the long axis of the body. So that's why we call them oblique muscles. And these are the external oblique muscles because they're more superficial. There are also deeper oblique muscles known as the internal oblique muscles that have also an oblique orientation just running the opposite direction. So here I'm highlighting internal obliques. And then out here you can see external obliques are running also 45 degrees relative to the long axis of the body. But they're just roughly 90 degrees relative to the internal obliques for the external obliques. Then even deeper than the internal obliques there are more abdominal muscles. The transversus abdominis is running transverse to the long axis of the body or they're running at 90 degrees relative to the long axis of the body. And the last of the major abdominal muscles is rectus abdominis. So rectus abdominis the word rectus comes from straight. So the rectus abdominis runs straight up and down parallel to the long axis of the body. So this is rectus abdominis here that's running straight up and down. And perhaps you'll notice that there's this rectus sheath of tendon and fibrous connective tissue. So the rectus abdominis gets separated into compartments little muscle bellies. And this will create the toned six pack abdomen when the rectus abdominis muscles are visible on somebody who has really toned abs. So the actions of the abdominal muscles enable flexion of the vertebral column. So if you're doing a sit up that's the action of flexing the vertebral column and then so the opposite is extension. So in this illustration the person is standing upright and then as they go to bend over as they're bending down they're performing flexion of the vertebral column. And then as they stand back up straight that's extension of the vertebral column. We'll also see flexion and extension are used to describe the movement of other joints like the shoulder, elbow, hip and knee. So in this illustration on the left here we can see the action of flexion of the knee. So flexion of the knee is to bend the knee. If you're starting in the straight upright position in anatomical position flexion is bending the knee. So it's moving through the sagittal plane to perform that action of flexion. And it's moving away from anatomical position as you flex the knee. Then as you extend the knee you're returning back to anatomical position so that word extension should make sense that you're extending the knee to make the leg straight with the thigh. Now you can also perform flexion and extension at the shoulder as is shown in the top of this illustration. Flexion of the shoulder is again movement through the sagittal plane. If we start in anatomical position during flexion the arm moves anteriorly and superiorly through the sagittal plane. And then extension is just the opposite of flexion so at the shoulder extension is moving back down into anatomical position. Similarly you can perform flexion and extension of the head at the neck as we see on the right here. So to bend the neck down is flexion and extension is to then bring the neck back up straight. So the external abdominal oblique is attached to the ribs and that's what we call the origin the part that doesn't move. It's also attached on the other end to the ilium and so that when you perform the action when you contract the external abdominal oblique it enables you to flex the vertebral column. So if you could think of that action if you were to flex the vertebral column like when you're doing a sit up external abdominal obliques can do that action. But also to rotate the vertebral column so if you were to do a sit up and twist your torso as you're doing the sit up that twisting would be to rotate the vertebral column. And so that's the type of sit up you would need to do if you really wanted to tone your external abdominal oblique muscles. So the location is the abdominal region superficially and laterally in the abdominal region between ribs 5 through 12 and the ilium. And the action is to flex or rotate the vertebral column. So in this illustration we can see the rectus abdominis. Rectus abdominis is found along the midline of the abdomen and the muscle has its origin down on the pubis part of the coxal bone on the midline. And then its insertion on the sternum as well as the costal cartilage the cartilage attaching the ribs to the sternum. And the action is to flex the vertebral column like when you do a sit up. So rectus abdominis is that muscle that when it becomes toned gives you a nice six pack of abs. And doing that action flexing the vertebral column doing sit ups is how you would work on toning your six pack. Now we'll focus on the muscles that move the elbow joint on the anterior brachial region. The large superficial muscle is known as the biceps brachii. So biceps brachii the word biceps means two heads. So there's a short head as well as a long head of the biceps brachii. And then the last part of that word brachii refers to the brachial region. So biceps brachii is found on the anterior brachial region and it performs the action of flexion. It flexes the elbow joint. So the biceps brachii flexes the elbow joint and it's found on the anterior of the brachial region. So there's a similar muscle found on the posterior of the brachial region triceps brachii. So triceps means three heads. There's a lateral head of the triceps brachii. There's a long head of the triceps brachii and there's also a medial head of the triceps brachii. That's not really easy to view from this angle. It would largely be deep underneath the long head of the triceps brachii. But on the distal end a small portion on the medial side of the brachial region is visible superficially. So the triceps brachii has three heads and is found on the posterior brachial region. And it performs the opposite action to what we saw for the biceps brachii. So it's on the opposite side, on the posterior instead of the anterior. Its action is to extend the elbow joint. So biceps brachii has an origin from the scapula and an insertion on the radius. And this enables the action of flexion of the elbow which is also known as the humeral ulnar joint. The triceps brachii located on the posterior brachial region has an origin from the scapula as well as the humerus. Inserts on the ulna and performs the action of extension at the elbow joint also known as the humeral ulnar joint. Now here we have a posterior view looking at the muscles of the pectoral girdle or the shoulder region. So the trapezius muscle is a large superficial muscle found in the posterior along the midline. So it's found on the posterior of the thoracic region along the midline as well as found on the posterior of the cervical region along the midline. The trapezius also attaches to the posterior of the cranium and all along the midline down along the vertebrae. And so that's what we call the origin of the muscle. Trapezius inserts onto the scapula and clavicle. So the pectoral girdle, the scapula and clavicle are the bones that move when trapezius contracts. So trapezius will elevate or depress. So if you are to move your shoulders, to shrug your shoulders, those are the actions the trapezius can perform to elevate to raise the shoulders superiorly, raise the pectoral girdle superiorly, that is, and then depress to lower the pectoral girdle inferiorly. So the rhomboidius minor and rhomboidius major are found deep to the trapezius and also contribute to moving the scapula. And then another superficial muscle that we can see in this view that's a major muscle we'll focus on is the deltoid. So the deltoid gives the shape to the acromial region or gives shape to the shoulder. So it's a superficial muscle found in the acromial region. The word deltoid means triangular shape, so this muscle does have a triangular shape. And we'll see the action is going to be movement of the shoulder joint, what we call abduction of the shoulder joint, or ABduction to help make clear the way that it's spelled abduction, ABduction. The opposite of that movement is called adduction with a D. So first we'll go through the little bit more details of the trapezius. So here you can see the trapezius has an origin all along the midline from the occipital bone down along the vertebrae from C1 to T12. Then the insertion of trapezius is on the scapula and clavicle, enabling the action of elevation of the pectoral girdle or depression of the pectoral girdle. And also we can retract the pectoral girdle with the trapezius. Now here we see several muscles that are responsible for movement of the shoulder joint. The deltoid you can see in this image has a triangular shape. So the deltoid gets its name from that triangular shape. So it's a triangular shape muscle found superficially in the acromial region. And the deltoid will have the action of abduction of the shoulder joint. The two other muscles that we can see here in this view will work opposite to the deltoid. So they will perform the action we call adduction. Here we see latissimus dorsi, which is a large superficial muscle found on the posterior of the abdominal region. So the origin of latissimus dorsi is along the lumbar vertebrae. And it may be surprising at first that this muscle that's found in the lower back in the posterior of the abdominal region is a muscle that moves the shoulder joint, but it does attach to the humerus, enabling latissimus dorsi to perform the action of abduction and also extension at the shoulder joint. So this large muscle found there in the posterior of the abdominal region is latissimus dorsi. And then coming around to the anterior view in the mammary region, here we can see pectoralis major. So pectoralis major is another muscle that contributes to the action of abduction of the shoulder joint. So while the deltoids will abduct, lift the arm at the shoulder joint, the pectoralis major and latissimus dorsi will abduct or lower the arm at the shoulder. And this is movement that's through the coronal or frontal plane as a contrast with flexion and extension that are moving through the sagittal plane. So in this illustration here, we can see the actions of abduction and abduction at the shoulder joint. So if we start in the anatomical position and we lift the arm at the shoulder, superiorly and laterally away from the midline, that is abduction. It might help you to think about the common root of the word abduction. A similar word, abduction, used in a different context means to steal away. So if you are out with a child and you're supposed to be watching the child but you get distracted and all of a sudden they've been stolen away by some other person, what happens is called abduction. Similarly, if the aliens come and take you away, that's abduction. You don't want to be abducted by aliens, you don't want to be stolen away. So abduction has that meaning of taking away. Here if you start in anatomical position with the arm right next to the torso, abduction is moving the arm away. It's moving it out away from the midline. Abduction is essentially the opposite of abduction, so abduction adds back. So if abduction takes it away from the midline, abduction brings it back to the midline. So of course those two words sound very similar, so I like to pronounce abduction, abduction sometimes just to emphasize that it's not adduction spelled with a D. The pectoralis major is a large superficial muscle found in the mammary region that has its origin, its stationary attachments. Along the clavicle and sternum, and then inserts on the humerus. So when it contracts it will perform the action of moving the humerus at the shoulder. And one of the major movements performed, one of the major actions of pectoralis major is to adduct the shoulder, moving the humerus back towards the midline through the coronal plane, the opposite of abduction. Pectoralis major can also flex the shoulder, so moving through the sagittal plane, raising the humerus anteriorly and superiorly is to flex the shoulder. And when you want to tone your pectoralis majors to get nice developed pecs, what kind of exercise can you perform? Well a bench press is a common exercise used, and with a bench press you are performing flexion of the shoulder joint and also a small amount of abduction of the shoulder joint. But it's primarily flexion of the shoulder joint, that would be the motion you'd perform when doing a bench press. So the deltoid, the triangular shaped muscle found superficially in the acromial region, has an origin from the clavicle and scapula and then inserts on the humerus, enabling the action of abduction, abduction of the shoulder joint. You'll notice here that I also put in parentheses another term for the shoulder joint, glenohumeral joint is just a synonym for the shoulder joint, but the deltoid performs abduction of the shoulder or glenohumeral joint, but that's not the only action of the deltoid. You can see the deltoid has the actions of flexion and extension at the shoulder joint as well. Now that will depend upon which portion of the deltoid muscle contracts. There are more anterior muscle fibers in the deltoid that can contract to enable flexion at the shoulder joint. And then the more posterior region of the deltoid can contract to enable extension, the opposite action at the shoulder joint. Now here we see with a posterior view, the large superficial muscle that's found on the posterior of the abdominal region known as latissimus dorsi. So latissimus dorsi, the dorsi part of that word refers to the dorsal region which is where we have the origin for this muscle. So the lumbar vertebrae as well as the more inferior thoracic vertebrae serve as the origin for latissimus dorsi. The insertion is on the humerus enabling this muscle to perform the action of adduction as well as extension at the shoulder joint. Now moving down to the lower limb, gluteus maximus is a large superficial muscle that gives shape to the gluteal region. So it's found on the posterior of the coxal bone, the posterior of the hip forming the buttocks or the gluteal region. So gluteus maximus is not the only muscle found in the gluteal region, it's just the largest, gluteus maximus is actually the largest muscle in the body, but also the largest of the gluteal muscles. So the gluteus maximus attaches at the ilium, the sacrum and the coccyx. The ilium is the more superior portion of the coxal bone, but all along the posterior of the pelvis really, along the ilium, sacrum and coccyx is the origin for gluteus maximus. The insertion of gluteus maximus is onto the femur and this enables the action of extension of the hip joint. You'll notice the hip joint is also known as the acetabulofemoral joint, but for this class we can use the simpler word hip joint. So gluteus maximus has the action of extension of the hip joint and if you stand up straight, you are extending the hip joint. So to bend the thigh at the hip, raising that thigh superiorly and anteriorly from anatomical position would be flexion of the hip joint. Gluteus maximus performs the opposite. It extends the hip joint, so as you stand up straight, you're contracting the gluteus maximus. And gluteus maximus can also lateral rotate the hip, so lateral rotate is moving the hip so that the knee would then point out laterally, so that the patellar region would point out laterally, the anterior of the knee. Now here we have an anterior view of the thigh of the femoral region where we can see the quadriceps femoris muscle group. So I'll highlight the major muscles that form quadriceps femoris. There's rectus femoris. There's vastus lateralis. There's vastus medialis. And there is a fourth muscle known as vastus intermedius, which is not visible in this illustration because vastus intermedius is located deep underneath rectus femoris. So you would have to cut rectus femoris to be able to see underneath to view vastus intermedius, but that's four separate portions of this muscle group known as the quadriceps femoris. The quadriceps femoris muscles perform the action of extension at the knee joint. So quadriceps femoris muscles extend the knee so that the leg and hip are straight, such as when you're standing up straight. So here we can see quadriceps femoris has an origin from the ilium and the femur. So there's four separate muscle compartments, and that's why we call it quadriceps. So the rectus femoris has its origin from the ilium, but the other three quadriceps muscles, the vastus lateralis, vastus medialis, and vastus intermedius all have their origins from the femur. Then the entire quadriceps femoris muscle group inserts together onto the patella and then down to the tibia. So while the tendons of these muscles attach to the patella, there's a ligament, the patella ligament, connecting from the patella to the tibia. And that enables this muscle to perform the action of extension of the knee joint. So the knee joint is also known as the tibiofemoral joint, the joint between the tibia and the femur. And extension of the knee joint, the action of the quadriceps femoris will enable you to stand up straight. Now here we have a posterior view where we can see the hamstrings muscle group. So I'll go ahead and highlight the major muscles of the hamstrings group. We have on the medial side here, semi-membranosis and semi-tendinosis. And then on the lateral side, we have biceps femoris. So biceps femoris itself is two separate muscle groups, biceps means two heads. So there's a long head of biceps femoris as well as a short head of biceps femoris. And those are both located on the lateral side on the posterior femoral region. Now if we look at semi-membranosis and semi-tendinosis, these are both found on the medial side of the posterior femoral region. But semi-tendinosis is more superficial than semi-membranosis. So semi-tendinosis is found superficially to semi-membranosis. Semi-membranosis runs deep to semi-tendinosis, but they're both found medial to biceps femoris. And together, biceps femoris, semi-membranosis and semi-tendinosis form the hamstrings muscle group. Here we can see an illustration of the hamstrings muscle group highlighting biceps femoris. That has an origin on the ischium and an insertion on the fibula and tibia. So the fibula is on the lateral side and that should help you remember biceps femoris is on the lateral side of the hamstrings. And the action of the hamstrings muscle group is to flex the knee or tibiofemoral joint. Now here we can see on the medial side the superficial muscle semi-tendinosis has an origin from the ischium and an insertion on the tibia enabling the action of flexion at the knee. Now deep under semi-tendinosis we can see semi-membranosis. So in this view, both muscles are visible, but I've highlighted semi-membranosis so you can see the portions of it that are visible with a superficial view. The rest of the muscle is deep running underneath semi-tendinosis. Similar to the origin and insertion for semi-tendinosis, semi-membranosis has its origin on the ischium and its insertion on the tibia, enabling the action of flexion at the knee joint.