I’m so glad that you just guys aren’t 5 years previous! In case you had been all in, like, kindergarten, the one approach I may train you about your skeletal system can be to sing you that silly music. You already know, “The toe bone’s related to the foot bone, the foot bone’s related to the ankle bone…the ankle bone’s related to the leg bone.” Like apparently there’s one leg bone. For the needs of instructing college-level anatomy and physiology, let’s simply say that that music is … reductive. Inadequate. For that music to be in any respect helpful for remembering all 206 bones that make up your skeletal construction, it must start with one thing like: “The distal phalanx is related to the center phalanx …” after which finish with one thing like: “the frontal bone meets the parietal bone alongside the coronal suture.” And it will most likely take like two and a half hours to sing the entire thing. However there’s far more to learn about your skeletal system than simply the names of the bones. In addition to bones, there’s cartilage and fibrous connective tissue that permits them to work collectively. And possibly extra importantly, if you happen to’re going to gonna discuss in regards to the physiology of your skeleton, you need to discuss joints. Joints are the assembly locations between two or extra bones — and regardless that it may not sound mathematically doable, you even have extra joints in your physique than you might have bones. In a number of locations — like your fingers and toes — every particular person bone is a part of extra than one or two joints. After which there’s the matter of what all that bone, cartilage, connective tissue — and the joints that they kind — really work collectively to do. And that’s … transfer. Physique actions occur when muscle tissues contract throughout joints, transferring one bone towards one other. And finding out the various kinds of actions your physique is able to, shouldn’t be solely fairly enjoyable, it’s additionally the most effective sensible methods to grasp your bones and joints. In case you ask me, all of that’s infinitely extra fascinating than memorizing what goes the place and pretending like a “spine” is admittedly an anatomical construction. So. Aren’t you glad you’re a grown-up? Dont fear, it’s not anybody you knew. It’s plastic, and it’s slightly bit smaller than the typical grownup skeleton. However — aside from having me stand in entrance of a large x-ray machine for 10 straight minutes — I can’t consider a greater strategy to stroll you thru the most important anatomical buildings of your skeleton. Now, if you happen to managed to retain our introduction to human bones final week, you’ll recall that anatomists sometimes divide the skeleton into two main components: the axial and the appendicular. The axial construction contains all 80 midline bones that kind your cranium, vertebral column, and thoracic cage. Beginning on the high right here, your cranium’s eight cranial and fourteen facial bones kind your physique’s most advanced bony construction, coming collectively to do some fairly nice issues, like shield your mind, show you how to see, odor, hear, eat, and , have a face. The 33 irregular bones in your vertebral column begin along with your atlas vertebra — the one which holds up your cranium, and is known as for the Greek god Atlas, who held the world on his shoulders as a punishment. I’m not saying you’ve bought an enormous head or something. I’m simply saying that’s what it’s referred to as. The vertebrae run down out of your cranium to your pelvis, offering the central help in your higher physique and finishing the enormously essential job of defending your spinal twine — the primary communication line between practically all your physique, and your mind. Most of your important organs are protected by the 12 pairs of ribs and dagger-like sternum that collectively comprise your thoracic cage, which additionally supplies attachment factors for your again, chest, shoulder, and neck muscle tissues. Now, the appendicular skeleton contains your higher and decrease limb appendages and pectoral and pelvic girdles that connect to the axial skeleton on the shoulder and the thigh. And regardless that your legs and arms clearly serve totally different capabilities — except you spend a number of time strolling round in your fingers or selecting stuff up along with your toes — each units of limbs share an analogous set-up. They’re every composed of three main segments — a standard association we see in a great deal of animals all the way in which again to fish, which anatomists discuss with as “one bone, two bones, a lot of bones and digits.” We are able to’t all be Dr. Seuss. And that’s nearly sufficient anatomy for this plastic skeleton to pay for itself. I’d quite concentrate on the physiology of the skeleton, and to be able to do this, we’ve bought to speak about joints. As is usually the case in anatomy, we classify joints each by what they’re made from, and by what they do. As a result of kind follows operate, we won’t actually discuss one with out speaking in regards to the different. So, the structural classification of your bones is all about what sort of materials binds these bones collectively — like, is it a fibrous tissue or cartilage, or a particular fluid-filled joint cavity. However the practical classification focuses on how a lot that joint can transfer. So, for instance, you might have joints in your physique that don’t transfer in any respect. These embrace, say, the joints between the bones that make up your skull. These non-moving joints are referred to as synarthroses. However you even have joints that transfer solely barely, just like the spot the place your two pubic bones meet to kind your pelvis. That joint exists primarily to soak up shock from strolling and operating, nevertheless it additionally has confirmed very useful throughout issues like childbirth. These partly-moving joints are referred to as amphiarthroses. Lastly, there are the diarthroses, that are totally movable, like your basic knee and elbow joints. They’re largely present in your limbs. However if you happen to ultimately end up within the enterprise of inspecting and treating individuals’s joints — and there are a number of docs who do — then it’ll be particularly helpful to know the structural classifications. Structurally talking, you’ve bought fibrous, cartilaginous, and synovial joints. Fibrous joints join bones with dense fibrous connective tissue, and are largely immovable — like these sutures between your cranium bones. As you may guess, your cartilaginous joints unite bones utilizing cartilage, and are comparable to their fibrous brethren in that they don’t transfer very a lot, and so they lack a joint cavity. However the household of joints that make all of the sports activities, and the complete artwork of breakdancing, and yoga doable, are the freely movable synovial joints. Most joints in your physique fall into this class. Though they do make use of cartilage and fibrous connective tissues like ligaments, they’re totally different in that the bones they be a part of are separated by a fluid-filled joint cavity. The cool factor about these cavities is that they include a little bit of viscous, egg-white-like synovial fluid that acts like grease on a hinge. With out that lubricant, simply operating down the road may trigger sufficient friction not solely to wear down your joint surfaces, however really overheat your joints sufficient to basically prepare dinner the encircling tissue and depart your legs smoking like a determined Looney Tunes character. These freely moveable synovial joints are available six totally different configurations that collectively enable just about any motion your physique could make, from a refined head nod to a vigorous leaping jack. All of which you can see in motion at your typical dance occasion. Critically, although, dance events are a wonderful place to check skeletal physiology. I imply let’s simply take this from my perspective: I’m at my highschool promenade. I’m carrying a tux that’s actually uncomfortable and I’m feeling form of shy, standing on the sting of the group. Possibly I need to take a look at the waters out slightly bit with like slightly hand dancing. Simply the hand going. Waving my hand back and forth — it’s a sort of gliding motion, one that happens when one flat bone floor glides over one other. All these motions use gliding, or aircraft joints, just like the one between the distal ends of your radius and ulna, and the carpal bones of your wrist. However say after some time I really feel like these gliding actions simply aren’t sufficient to totally specific myself. I’ve to enlist the extra versatile angular actions. These are the kinds of movement that both improve or lower the angle between two bones throughout any aircraft within the physique, like if I bob my head, or kick my leg up, or elevate the roof. If individuals nonetheless do this. If that bending movement decreases the angle of the joint and brings these bones collectively, like once I bend my arm collectively, that motion known as flexion. Once I bend it again, I’m growing that angle, and it’s referred to as extension. And if I proceed that movement past my regular anatomical positioning, and it’s considerably harmful, that known as hyperextension. These motions enlist the hinge joints. Equally, my oval-shaped condylar knuckle joints enable my fingers to bend and ball up for an excellent fist pump. Now I’m getting tremendous into it. I would like elevate my arms up over my head. Properly, the act of elevating my arms away from my physique known as abduction, whereas transferring them again down towards the physique known as adduction. And this right here, like, lasso motion? That’s circumduction — a mixture of all 5 of these actions that enable the forearm to maneuver in a circle whereas the elbow joint stays comparatively steady. Which actually makes you wanna give credit score to these cowboys. Now if you wish to get actually critical about that lassoing and develop it sufficient to incorporate the complete arm, the transfer ultimately will morph from an angular motion to a rotational one — a movement that turns the bone round its axis, on this case, the humerus. Hip and shoulder joints use a ball-and-socket design that enable rotational motion, however the extra versatile a joint is, the extra unstable and fragile it’s — which is one cause why you see so many dislocated shoulders and hip replacements. And it’s price stating that some actions are simply particular and distinctive and peculiar, and solely happen in a number of choose joints — particularly in your fingers, toes, and jaw. For instance, your capacity to the touch your thumb to your fingertips or give a thumbs up is due to opposition motion, facilitated by your saddle joint, which makes your thumbs opposable. The pivot joint between your radius and ulna mean you can rotate your palm ahead or anteriorly in a movement referred to as supination, and turning it backward or posteriorly known as pronation. In order that’s what I prefer to assume is the extra grown-up method to instructing you about your skeleton. It didn’t contain any singing, however sure, slightly dancing. And it was price it, since you discovered in regards to the primary construction of your skeletal system, together with the preparations of each the axial and the appendicular skeleton. And we went over the structural and practical classifications of your joints, together with the most important varieties of motion that they make doable. Particular due to our Headmaster of Studying Thomas Frank for his help for Crash Course and free schooling. This episode was co-sponsored by Greg Avarbuch, Faht-Mah ikh-Bahl, and Ricky D. Shields. Thanks to all of our Patreon patrons who assist make Crash Course doable by their month-to-month contributions. In case you like Crash Course and need to assist us make nice new movies like this one, you’ll be able to take a look at patreon.com/crashcourse Crash Course is filmed within the Physician Cheryl C. Kinney Crash Course Studio. This episode was written by Kathleen Yale, edited by Blake de Pastino, and our guide, is Dr. Brandon Jackson. Our director is Nicholas Jenkins, the editor and script supervisor is Nicole Sweeney, our sound designer is Michael Aranda, and the graphics group is Thought Café.