Joints: Crash Course A&P #20

Joints: Crash Course A&P #20

I am so glad that you guys are not five years
old! If you were all in, like, kindergarten, the
only way I could teach you about your skeletal system would be to sing you that stupid song. You know, “The toe bone’s connected to
the foot bone, the foot bone’s connected to the ankle bone…the ankle bone’s connected
to the leg bone.” Like apparently there’s one leg bone. For the purposes of teaching college-level
anatomy and physiology, let’s just say that that song is … reductive. Insufficient. For that song to be at all useful for remembering
all 206 bones that make up your skeletal structure, it would have to begin with something like:
“The distal phalanx is connected to the middle phalanx …” and then end with something
like: “the frontal bone meets the parietal bone along the coronal suture.” And it would probably take like two and a
half hours to sing the whole thing. But there is way more to know about your skeletal
system than just the names of the bones. In addition to bones, there’s cartilage and fibrous
connective tissue that allows them to work together. And maybe more importantly, if you’re going
to gonna talk about the physiology of your skeleton, you have to talk about joints. Joints are the meeting places between two or
more bones — and even though it might not sound mathematically possible, you actually have
more joints in your body than you have bones. In a lot of places — like your hands and
feet — each individual bone is part of more than one or two joints. And then there’s the matter of what all
that bone, cartilage, connective tissue — and the joints that they form — actually work
together to do. And that is … move. Body movements happen when muscles contract
across joints, moving one bone toward another. And studying the different types of movements
your body is capable of, is not only pretty fun, it’s also one of the best practical
ways to understand your bones and joints. If you ask me, all of that is infinitely more
interesting than memorizing what goes where and pretending like a “backbone” is really
an anatomical structure. So. Aren’t you glad you’re a grown-up? Dont worry, it’s not anyone you knew. It’s plastic, and
it’s a little bit smaller than the average adult skeleton. But — other than having me stand in front
of a giant x-ray machine for 10 straight minutes — I can’t think of a better way to walk you through
the major anatomical structures of your skeleton. Now, if you managed to retain our introduction
to human bones last week, you’ll recall that anatomists typically divide the skeleton
into two major parts: the axial and the appendicular. The axial structure includes all 80 midline bones that
form your skull, vertebral column, and thoracic cage. Starting at the top here, your skull’s eight
cranial and fourteen facial bones form your body’s most complex bony structure, coming
together to do some pretty great things, like protect your brain, help you see, smell, hear,
eat, and you know, have a face. The 33 irregular bones in your vertebral column
start with your atlas vertebra — the one that holds up your skull, and is named for the Greek god Atlas,
who held the world on his shoulders as a punishment. I’m not saying you’ve got a huge head or anything.
I’m just saying that’s what it’s called. The vertebrae run down from your skull to
your pelvis, providing the central support for your upper body and completing the enormously
important job of protecting your spinal cord — the main communication line between nearly
all of your body, and your brain. Most of your vital organs are protected by
the 12 pairs of ribs and dagger-like sternum that together comprise your thoracic cage,
which also provides attachment points for your back, chest, shoulder, and neck muscles. Now, the appendicular skeleton includes your
upper and lower limb appendages and pectoral and pelvic girdles that attach to the axial
skeleton at the shoulder and the thigh. And even though your arms and legs clearly
serve different functions — unless you spend a lot of time walking around on your hands
or picking stuff up with your feet — both sets of limbs share a similar set-up. They’re each composed of three major segments
— a common arrangement we see in loads of animals all the way back to fish, which anatomists
refer to as “one bone, two bones, lots of bones and digits.” We can’t all be Dr. Seuss. And that’s just about enough anatomy for
this plastic skeleton to pay for itself. I’d rather focus on the physiology of the skeleton, and
in order to do that, we’ve got to talk about joints. As is often the case in anatomy, we classify
joints both by what they’re made of, and by what they do. Because form follows function, we can’t
really talk about one without talking about the other. So, the structural classification of your
bones is all about what kind of material binds those bones together — like, is it a fibrous tissue
or cartilage, or a special fluid-filled joint cavity. But the functional classification focuses
on how much that joint can move. So, for example, you have joints in your body
that don’t move at all. These include, say, the joints between the bones that make up your cranium.
These non-moving joints are called synarthroses. But you also have joints that move only slightly,
like the spot where your two pubic bones meet to form your pelvis. That joint exists mainly
to absorb shock from walking and running, but it also has proven very handy during things
like childbirth. These partly-moving joints are called amphiarthroses. Finally, there are the diarthroses, which
are fully movable, like your classic knee and elbow joints. They’re mostly found in
your limbs. But if you eventually find yourself in the
business of examining and treating people’s joints — and there are a lot of doctors who
do — then it’ll be especially useful to know the structural classifications. Structurally speaking, you’ve got fibrous,
cartilaginous, and synovial joints. Fibrous joints connect bones with dense fibrous
connective tissue, and are mostly immovable — like those sutures between your skull bones. As you might guess, your cartilaginous joints
unite bones using cartilage, and are similar to their fibrous brethren in that they don’t
move very much, and they lack a joint cavity. But the family of joints that make all the
sports, and the entire art of breakdancing, and yoga possible, are the freely movable
synovial joints. Most joints in your body fall into this category. Although they do make use of cartilage and
fibrous connective tissues like ligaments, they’re different in that the bones they join
are separated by a fluid-filled joint cavity. The cool thing about these cavities is that
they contain a bit of viscous, egg-white-like synovial fluid that acts like grease on a
hinge. Without that lubricant, just running down
the street could cause enough friction not only to wear out your joint surfaces, but
actually overheat your joints enough to essentially cook the surrounding tissue and leave your legs
smoking like a desperate Looney Tunes character. These freely moveable synovial joints come
in six different configurations that together allow pretty much any movement your body can make,
from a subtle head nod to a vigorous jumping jack. All of which you will find in action at your
typical dance party. Seriously, though, dance parties are an excellent
place to study skeletal physiology. I mean let’s just take this from my perspective:
I’m at my high school prom. I’m wearing a tux that is really uncomfortable and I’m feeling
kind of shy, standing on the edge of the crowd. Maybe I want to test the waters out a little
bit with like a little hand dancing. Just the hand going. Waving my hand from side to
side — it’s a type of gliding movement, one that occurs when one flat bone surface
glides over another. All these motions use gliding, or plane joints,
like the one between the distal ends of your radius and ulna, and the carpal bones of your
wrist. But say after a while I feel like these gliding
movements just aren’t enough to fully express myself. I have to enlist the more versatile
angular movements. These are the types of motion that either
increase or decrease the angle between two bones across any plane in the body, like if
I bob my head, or kick my leg up, or raise the roof. If people still do that. If that bending motion decreases the angle
of the joint and brings those bones together, like when I bend my arm together, that movement
is called flexion. When I bend it back, I’m increasing that
angle, and it’s called extension. And if I continue that motion beyond my normal
anatomical positioning, and it’s somewhat dangerous, that is called hyperextension. These motions enlist the hinge joints. Similarly,
my oval-shaped condylar knuckle joints allow my fingers to bend and ball up for a good
fist pump. Now I’m getting super into it. I might like
raise my arms up over my head. Well, the act of raising my arms away from my body is called
abduction, while moving them back down toward the body is called adduction. And this here, like, lasso movement? That’s
circumduction — a combination of all five of those movements that allow the forearm to move
in a circle while the elbow joint stays relatively stable. Which really makes you wanna give credit to
those cowboys. Now if you want to get really serious about
that lassoing and expand it enough to include the entire arm, the move eventually will morph
from an angular movement to a rotational one — a motion that turns the bone around its
axis, in this case, the humerus. Hip and shoulder joints use a ball-and-socket
design that allow rotational movement, but the more flexible a joint is, the more unstable
and fragile it is — which is one reason why you see so many dislocated shoulders and hip
replacements. And it’s worth pointing out that some movements
are just special and unique and weird, and only occur in a few select joints — especially
in your hands, feet, and jaw. For example, your ability to touch your thumb
to your fingertips or give a thumbs up is thanks to opposition movement, facilitated by your
saddle joint, which makes your thumbs opposable. The pivot joint between your radius and ulna
allow you to rotate your palm forward or anteriorly in a motion called supination, and turning
it backward or posteriorly is called pronation. So that’s what I like to think is the more grown-up
approach to teaching you about your skeleton. It did not involve any singing, but yes, a
little dancing. And it was worth it, because you learned about
the basic structure of your skeletal system, including the arrangements of both the axial
and the appendicular skeleton. And we went over the structural and functional classifications
of your joints, along with the major types of movement that they make possible. Special thanks to our Headmaster of Learning
Thomas Frank for his support for Crash Course and free education. This episode was co-sponsored by
Greg Avarbuch, Faht-Mah ikh-Bahl, and Ricky D. Shields. Thank you to all of our Patreon patrons who
help make Crash Course possible through their monthly contributions. If you like Crash Course
and want to help us make great new videos like this one, you can check out Crash Course is filmed in the Doctor Cheryl
C. Kinney Crash Course Studio. This episode was written by Kathleen Yale, edited by Blake
de Pastino, and our consultant, 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 team is Thought Café.

100 Replies to “Joints: Crash Course A&P #20”

  1. Youโ€™re smart, but all I can hear is Alton Brown from Food Network. Then I get distracted and start thinking about snacks.

  2. Painfull Temperomandibular dislocation types and relocation open Google Doc Rajendra sheregar And see images videos litreture medical science

  3. Omg Americans, I gotta hand this one to you. Naming the bones after the latin names is so easy (in logical way) and just makes it extremely less confusing to learn. Meanwhile in my country we have our own translations for the bones and while the names might make sense in our language they are nothing like the Latin names… Which brings me here. Since I love English I hoped that it'd help me a bit to listen to this video.

  4. I'm elven dude I just want to know what a double jointed leg looks like, it may sound weird but I'm double jointed in my legs and wanted too know….

    And from what I learned today on the great website Google that I do not have an extra amount of joints but I have something called joint hypermobility and I also have a high chance too get arthritis HIPPIE I HAVE A HIGHER CHANCE TO GET THE THING MY MUM HAS YAYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY AND BECAUSE SHE HAS IT I KNOW ALL THE PAIN IT CAUSES HER YAYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYYY I'm so screwed in life,

  5. In my elementary school we were forced to sing a song about there being 206 bones, but if one is broken there are still 205 left. Not only was it at a kindergarten level, but also immensely annoying because of how it suggested a bone magically disappeared by breaking. Breaking one bone doesn't make you have fewer bones! The broken one still exists, just in smaller pieces. You may even argue you have more bones.

  6. I did not realize there was so much more to Joint classification. The Synovial fluid is VERY important, without it your bones could cause enough friction to cook the surrounding tissue. The Synovial Joint has six different configurations which include the phane, hinge, condylar, pivot, ball & socket, and saddle, which was honestly something very interesting to hear about. Before watching this video I did not know the difference between Angular and Rotational movement. Now I know that angular is the motion that increases and decreases the angle between two bones across any plane (flexion, extension, hyper-extension, abduction, adduction, and circumduction are all part of it). Also that Rotational is the motion that turns the bone around on its axis. I had never into consideration that the Ball and Socket joints were so fragile, which now seems to make lots of sense. Thank you Crash Course for making everything so clear to me and helping me put together the puzzle pieces.

  7. i learned…
    1. you have more joints than bones
    2. you classify joints by what they do and what theyโ€™re made of
    3. there are 6 different kinds of synovial joints
    4. within each joint are different names for the movements they make possible

  8. 1. I learned that the more flexible a joint is, the more fragile and unstable it ultimately is. This makes sense when you look at the ratio of hip and shoulder dislocations, as opposed to other joint injuries.
    2. I learned that the Atlas Vertebra is named after the Greek God Atlas, who was forced to hold the weight of the world on his shoulders as punishment. This vertebra holds up our head, so the connection makes sense.

  9. Structural joint classifies what joints are made of and Functional joints classify what joints do. Fibrous joints are connected w dense fibrous connective tissue and do not move. I found it interesting that joint cavities are made up of fluid instead of a specific type of cartilage.

  10. In this crash course video, I found it very interesting and easy to understand.
    – I didn't know that there were more joints in your body than bones, I guess because I never thought about it.
    – The way he demonstrated all six different joint movements (plane, hinge, condylar pivot, ball & socket and saddle) made me remember what they all do.
    -The reason for why people dislocate that shoulders and hips so often now makes sense.

  11. In this video, I learned that synarthroses are joints that donโ€™t move at all while amphiarthroses move only a small amount. An example of an amphiarthrosis is the pubic symphysis that moves slightly to absorb shock. I also learned that diarthroses are fully mobile and are mainly located in the limbs. I then discovered the distinction between the fibrous, cartilaginous and synovial joints. Fibrous joints are connected through fibrous tissue and are mostly immobile. Cartilaginous joints are connected through cartilage and also donโ€™t move very much. Lastly, synovial joints are freely mobile, separated by a fluid-filled cavity and have 6 different, more specific types of joints. These 6 are plane joints, hinge joints, condylar joints, ball and socket joints, saddle joints and pivot joints.

  12. 1.)
    3 types of functional classification: Synarthroses(non-moving), Amphiarthroses(partly-moving), Diarthroses(fully-move).

    3 types of structural classification: Fibrous joints(connect bone with dense fibrous connective tissue). Cartilaginous: (unite bone), Synovial Joints (articular cartilage that covers opposing bone).

    There are many types of gliding movements such as flexion, extension, hyperoxtonsion
    abduction, adduction, circumduction.

  13. From this video I learned the different types of Structural classifications and how too differentiate them, and also how too differentiate the functional classifications

  14. you have more joints in your body than bones

    body movements happen when muscles contract across joints moving one bone toward another

    the more flexible a joint is the more unstable and fragile it is

  15. there are more joints than bones in the body!
    functional = movement
    structural = made of
    6 different synovial joints:
    ball and socket
    plane joint (gliding movement)
    saddle joint

    flexion-decreasing angle
    extension-increasing angle
    rotational-motion that turns bone around axis

  16. We came across this video because my 5-year-old was curious about how joints worked and he was very offended by your opening ๐Ÿ˜‚ lol.

  17. Iโ€™ma say it now, I hate joints, all there names are so similar and i have to make up dumb reasons why each one is which please oh hank green lend me your knowledge so that i may pass A&P, amen

  18. I hope this helps someone, my professor told me today to think about soupination like you are holding soup and that's one way I remember it because you can't hold soup with your palm facing behind you, you would hold soup like you hold most things, with it sitting on your palm

  19. The cartilage that makes up the external portion of your ear (the pinna) is actually neither of those two types of cartilage, but elastic cartilage (at least, that's why I learned in my own anatomy & physiology education). Absolutely love this and all these A&P videos, but the makers may want to edit that note at 0:47!

  20. Our mid-term exam is fast approaching but I find reading my notes all over again boring. Watching crash course is such a better and interesting way to review. Thank you for this <3

  21. WOW!!!!! You dancing analogy is GENIUS!!!!! What a fabulously practical, relative and memorable way to remember how the joints move/work!!! Excellent!!! THANK YOU!!!! ๐Ÿ’ƒ๐Ÿ•บ๐Ÿ˜€๐Ÿ‘๐Ÿป๐Ÿ’™

  22. How on earth can anyone give this a thumbs down?!??!!! ๐Ÿ˜ฑ The fist pump but is hilarious!!! Definitely helped me remember and relate to how joints move and work!! Brilliant!!

  23. These videos have been helping me pass anatomy. I love these videos ๐Ÿ˜‚๐Ÿ“š๐Ÿ“โœ๐Ÿ™Œ๐Ÿผ So helpful!!

  24. Why are you better than my professor at explaining this?? Thank you so much for all your videos I got them on repeat!๐Ÿ˜‚

  25. I have to slow the video you know what i said when i slow it? "You know what i cant still understand if i slow it" so i just went to normal gosh darnit!!!!! Y u speak so fast your grate. and all but you need to slow it sometimes… Look at that guy on MathAntics his Good at explaining and he even slow it out im not "comparing" you to him at all.

  26. i want to ask if i can take some part of your videos to explain it in another language on youtube ?

  27. This is genuinely the funniest content I've found on youtube. I didn't come here for laughs, and I find myself laughing out loud. Hands out for you guys, thank you so much!

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