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First, let’s talk about bone tissue-that is, what are some of the cool stuff that makes up your bones? Both the outside and the inside? Also, what are some of the functions of bones as a result of this special tissue?

And we will note that anatomical/biological term for bone tissue is actually “osseous tissue”; anything “osseous” or with the prefix “osseo-” is talking about bones. –SQUEE!-

So the functions of bone are:

• Support: as awesome as we human beings are, we are not cephalopods that can just wiggle and lump and shimmy to get around, let alone function. We gotta have our bones supporting us as our framework; we gotta fit into a frame or else we ain’t even able to sit up in a computer chair and read this sentence. Our leg bones are very, very, very, very strong pillars that support our body trunk (AKA torso) and our ribs support our thorax (AKA chest) wall.

• Protection: Our bones also protect and anchor our soft organs. Our ribs actually encase what’s known as our “thoracic cavity” and it includes those really, vitally important organs such as our heart and lungs. Our vertebral/spinal column encloses and protects our brain and spinal cord.

• A note: common misconception that even I had years ago is that our “spinal cord” and “spinal column” are one and the same. Indeed, they are not: our spinal column is the actual bone that extends all the way from the base of our skull (bottom part of our head, right before our neck starts), all the way down our back, and down, down, down to our pubic symphysis (our hip/booty area). In contrast, our spinal cord is a very soft, fragile baby that runs inside the length of our spinal column and, of course, connects to our brain and works with our brain in sending all kinds of messages flying to-and-fro all over our body. Our spinal cord is encased in our spinal column and so it is protected by our spinal column.

• Movement: Our skeletal muscles use our bones as levers to move-in other words, our muscles are always pulling on our bones, never pulling. And so we move to scroll down this post!

• Storage: Yes, indeedy, our bones have fat storage in what’s known as our “yellow marrow”! Our bones also store very, very important minerals such as calcium and phosphorus.

Our bones can be classified by two things: the type of osseous tissue they have and by their shape. So the two types of osseous tissue are:

• “Compact bone”, which is hard, dense, and looks smooth and homogenous throughout. Note that it just looks that way, but it’s not. –winks-

• “Spongy bone”, which is also known as “cancellous bone”. It makes you think of Spongebob Squarepants, but it’s quite a bit stronger and they are not in the business of flipping Krabby Patties. Instead, they’re made of “trabeculae”, which are small, needlelike or flat pieces of bone that form an open network that’s filled with bone marrow. Spongy bone has lots of space and we’ll see soon that this is vital for our bone cells (“osteocytes”) to have a place to hang out and do their thing.

Then, our bone shapes:

• Long: These are basically all of our limb bones (AKA our “appendicular skeleton”), excepting our patella (knee), carpals (wrist), and tarsals (ankles). Note that the term “long” is only referring to the bone’s elongated shape, rather than the overall size. Our long bones are made of a “diaphysis”, which is the long shaft, and two “epiphyses”, which are the ends. They’re mostly made of compact bone, but can have tons of spongy bone, depending on the person.

• Short: These are kinda cubelike and are mostly made of spongy bone. They’re the ones that make up our wrist and ankles.

• Flat: Yes, they’re thin and flattened, but they can usually be kinda curved. These are our sternum (AKA breastbone), ribs, and most of our skull bones.

• Irregular: Last, but not least, these poor souls do not fit into any of the previous categories. Alas, they are outcasts, but much-needed outcasts. They typically have complicated shapes. They are some parts of our skull bones, our vertebrae, and our hip bones.

So remember when we said that compact bone looks smooth and homogenous, but…it’s not? And it wouldn’t be, right? Surely our compact bone isn’t just hard and smooth and dense all throughout, yes? If we were to take a cross/transverse section of it and peer down and inside, we wouldn’t just see uninterrupted bone?

Indeed, we would not! Our compact bone, while not exactly a freakin’ city like our skin, is riddled with canals and passageways! These give the conduits for nerves, blood vessels, and lymphatic vessels! So, uhh…kinda like a vast, fascinating subway system deep underneath the city that is our skin. And that subway system is made up of the following:

• “The Harversian/osteon system”, which is compact bone’s structural unit, meaning that it’s the most signature feature of compact bone. A lot of people just shorten it to “osteons” and keep it going. They’re elongated cylinders that run parallel to the bone’s long axis. They’re made of groups of what’s called lamellae.

• But then, what is lamella? “Lamella” is those onions of our bodies! Now first know that they’re hollow tubes inside the previously-mentioned osteons and they’re placed one inside the next, kinda like Easter eggs of bigger to smaller size or, well…like onion layers are placed one inside the next. They’re also made of collagen and one lamella’s collagen runs in one direction while the next one runs in the other direction. So you basically have one lamella running clockwise, the next running counterclockwise, and then the next running clockwise, and so on and so forth. The purpose of this? It makes our bones a very, very, very powerful structure that’s able to withstand twisting, tension, and other mechanical stresses. Ain’t that some fascinating shit? Be sure to thank your onion-lamella today, teehee!

• Incomplete lamella that are between the osteons are called “interstitial lamella” and lamella that are right next to the bone’s outer surface and extend around the bone’s whole circumference are “circumferential lamella” and these are the ones that most help resist bone twisting.

• Our “Haversian central canals” run straight through each osteon’s core and holds the little subway cars like small blood vessels and nerve fibers.

• Our “Volkmann’s/perforating canals” run at right angles to our bones’ long axis. This means that they do run parallel to the bone’s axis but, unlike the Haversian canals, they eventually take a right (or left, haha) turn to reach and meet directly with the bone. And the purpose of that is to connect the vascular and nerve supplies of the bone’s “periosteum” (basically its outer membrane) to the ones in the central canals and “medullary” (AKA middle; it holds our bone marrow) cavity. So think about a city’s subway system still needs some kind of connection to the upper/outside world for the city’s inhabitants to come and go, yes? That’s what our Volkmann’s are for!

• Next, ya’ll know that we have bone cells and they’re basically called “osteocytes”. Well, you’d think we have a problem with compact bone because compact bone is so dense where it doesn’t have all of these osteons and canals running through it. So…where do the osteocytes get to comfortably hang out and do their thing? Never fear! This is what our “lacunae” are for! These are hollowed-out spaces specifically for our osteocytes to hang out in. We have a lot of these in compact bone. Yay!

So now we know that our compact bone is a whole subway system complete with onions! From here, we can then conclude that our bone is a constantly dynamic, active tissue that’s always being remodeled, yes? It’s always being built up and broken down in a whole lotta ways!

• About 5%-7% of our bone is remodeled each week, in fact! It’s done by two different methods…

1. “Bone deposition”: this is done by bone cells known as “osteoblasts”, which build up bone (“b” for build!). Bone disposition happens when our bone has been injured and/or simply requires more strength. Now, our body is awesome in this deposition, but it needs our help! We can help by having as healthy and varied a diet as possible. Specifically, we’ll need a diet rich in protein (yeah, your muscles are by far not the only ones that need this), vitamins C, D, & A, and minerals such as calcium, phosphorus, magnesium, and manganese!

2. “Bone resporption”: this is done by bone cells known as “osteoclasts”, which break down bone (“c” for collapse!), the opposite of osteoblasts. Osteoclasts digest/dissolve bone’s organic matrix and then converts the calcium salts from that bone into a soluble form that easily passes into a solution…like your bloodstream, teehee!

• One of the ways that our bone remodeling is regulated is by our hormones and those hormones are mainly concerned with controlling how much calcium comes and go from our bloodstream via our bones and our diet. These two hormones are:

1. “Parathyroid hormone (PTH)”: This is triggered when calcium levels are too low in our blood. They stimulate osteoclast activity which, remember, digests/dissolves bone, and so releases that calcium into the bloodstream.

2. “Calcitonin”: This does the opposite from PTH. That is, it’s triggered when calcium levels are too high and they bring it back down. Yay!

Now, wanna know about different bones of the skeletal system? It is true that we have 206 bones in our body and our bones, along with our cartilage, joints, and ligaments, make up about 20% of our total body mass. Yay!

Let’s take a look at our skull to start with. First, it should be noted that it’s a very, very common misconception that our skull is just a big ol’ bone all by itself in our head. Now, it’s true that it’s one structure on its own, but our skull is actually made of a great many different bones…

• Our skull is made up of 22 bones total. That 22 are then divided into 8 “cranial bones” and 14 “facial bones”. There is a true, significant difference between the cranial and facial bones. To understand what our cranial bones are, think of the common cartoon renditions of Frankenstein, yes? And remember how you can always comically open up the top part of his head, like there’s a lid right there starting at his forehead? All of those bones inside Frankenstein’s head-inside our head-are the cranial bones. They are called as such because they are housed in our skull’s “cranium”, the area that our brain hangs out and does its things in. Meanwhile, our facial bones are a little easier to understand-as their name suggest, they are the bones of our face or just about everything outside and below our cranial bones. We can see and touch a great many of them, in fact!

• “Sutures” are immovable joints-the seams-of our skull. We have four of them that keep our skull together: coronal (AKA frontal), sagittal, lambdoid, and squamous.

• If anyone ever accuses you of being a snuggle bug, tell them that you get it from your brain…literally! Part of what keeps your brain rooted and stable in your skull are the three “cranial fossa”-these are internal bony ridges divided into the front, middle, and back of the cranium. Your brain snuggles right up against these and voila! Rooted, stable brain in your skull because of its three snuggle buddies!

• The “glabella” is the smooth part of the frontal bone between our orbits. In other words, if you touch your finger right between your eyebrows, you’re touching your glabella. I like that word, teehee…glabella.

• Our “foramen magnum” is a big ol’ hole right in the base (AKA occipital) part of our skull. It’s a hole that provides a passageway for our spinal cord, yay! And don’t freak out-we actually have a lot of holes referred to as “foramens” and “meatus” that allows for all kinds of nerves and blood vessels to pass through! Such a good thing!

• Touch your temples, the areas just above your ears. There are your “temporal bones”!

• Remember when I said we have a butterfly in our skull? Meet your “sphenoid bone”, which is literally made of a “greater wing” and a “lesser wing”! It spans the width of the cranial floor and is the keystone-the biggest player-in the cranium structure because its central wedge meets with all other cranial bones. In fact, lemme show you a picture of your sphenoid bone:

D’you see the greater and lesser wings? You see how it meets with so, so many other bones of your cranium? Cool butterfly is cool butterfly, yes?

• Open and close your mouth. You just used your “mandible”, also known as your jaw! It’s the largest and strongest of our facial bones! Now, if you open and close your mouth and press your fingers to the sides of your face just below your cheekbones (AKA zygomatic bone/zygomatic process) where you feel something moving as you open and close your mouth? Those are your “mandibular condyles”, or the hinges of your jaw; it’s our only movable bone in our face!

• Your “hyoid bone” is the only bone in the body that does not articulate (AKA meet) with another bone! It’s located in our throat mid-neck and is horseshoe shaped. Wow…we got onions, butterflies, and a horseshoe inside us. Whodathunk it?! Though our hyoid bone doesn’t have any friends in any other bones, it’s thankfully not lonely. It hangs out and is anchored by our “stylohyoid ligaments” to our “styloid process”! Our hyoid bone also has lots to do while it hangs out with its two friends: it provides a movable base for our tongues (If you wiggle your tongue around and notice something also moving in your throat at the same time? There ya go!); gives an attachment point for neck muscles that raises and lower our larynx during swallowing and speech.

So how about the vertebral column next? Here we go!

• It makes up about 2/5th of our total body height and do remember that it extends all the way from the base of our skull and down to our hip/booty area. It’s a very strong, flexible rod.

• Our vertebral column is divided up into regions that Mrs. A taught us to remember it as breakfast, lunch, and dinner like so:

1. In our necks, we have 7 cervical vertebrae. Our necks come first, like breakfast at 7:00.

2. In our back, we have 12 thoracic vertebrae. Our necks come in the middle, like lunch at 12:00.

3. In our lower back, we have 5 lumbar vertebrae. Our lower back comes last, like dinner at 5:00.

4. And lastly, we have five fused sacral and four fused coccygeal in our pelvis/hip area. Yay!

• Try to bend over as far as you can. You realize that, ideally at least, you can’t go very far before something in your back stops you because it’s been stretched as far as it can go. That’s thanks to your vertebral column’s “front ligaments”, which prevents such hyperextension.

• If you try to do the opposite by bending as far backwards as you can, you’ll find that you can’t go very far before you’re stopped yet again. That’s thanks to your vertebral column’s “back ligaments”, which prevent hyperflexion. Give it up for your ligaments!

• Roll your head around for a moment. You notice how there’s something in your neck that feels like a…pivot that allows you to do that? That pivot is the “dens or odontoid process of your axis”! Your “axis” is your second cervical vertebrae or “C2”. It’s “dens/odontoid process” is a tooth-like process (AKA projection) from the top part of its body; it projects upwards to meet with your “atlas”, your super-duper specially modified first cervical vertebrae or “C1”. Axis’ dens meets with a hole in the atlas to create a pivoting mechanism and so you can roll your head around with a wide range of moment!

• Our “lumbar vertebrae” or the vertebrae that’s part of our lower back are the largest and strongest of the vertebrae. This is because it’s designed with enhanced weight-bearing function and that is because it’s part of the body that receives our weight when we sit down.

Onto our “appendicular skeleton”, AKA our limbs and their attachment points (hips & shoulders)!

• Gently touch your clavicle. Then trace your fingers from your clavicle to your shoulder. Next, keep tracing your fingers around to your back and notice how your shoulder touches with your shoulder blades in the back. It’s all connected like a…frame, yes? And that frame is known as your “pectoral girdle”!

• The fancy-dancy long word for the day is “acromioclavicular joint”. It quite simply refers to the joint formed by the “acromion” your the scapula (AKA shoulder blade) meeting with your clavicles!

• Rotate your wrist. Your wrist bones are known as your “carpals”! If you’ve ever heard of “carpel tunnel syndrome”? Yeah, that’s talking about problems with your wrists often due to repetitive motions such as constantly typing.

• From your wrist, gently feel the bones of your palm. You’ll notice that your palm’s bones aren’t just a block or a cube, yes? In fact, it feels like there are things kinda thin and separated in there. They’re actually known as your “metacarpals” and you have a whopping five of them that extend up to your fingers.

• Now wriggle your fingers. Those are known as your “phalanges”! You have a proximal, middle, and distal in all of them except your thumb!

• And your thumb’s anatomical term is “pollex”…and I cannot tell you how much I love that word. “Pollex”. It’s so freakin’ adorable that I can’t even!

And now last, but certainly not least? Our “joints”! Joints are also known as “articulations”, or the area where two or more bones meet. They’re one of the biggest reasons we can move easily and why our bones don’t painfully grind against each other when they meet.

• Joints can be classified by their function, or the amount of movement they allow. Like so:

1. “Synarthrosis” are joints that are completely immovable. The prefix “Syn-” means fused together and so they are immobile.

2. “Amphiarthrosis” are slightly, kinda-sorta movable joints. Kinda like how an “amphibian” can slightly, kinda-sorta live on land and live on water, yes?

3. “Diarthrosis” are freely movable joints. They have great range of motion (ROM)!

• Didja know that your teeth are anchored to your gums by “fibrous joints”, which are completely immovable joints? And those fibrous joints are known as “gomphosis”! I remembered this for the test by saying to myself, “Your teeth gomp on gum and gobble on turkey…gomp, gobble, gomphosis!”

• Even if we may not know the term, our “synovial joints” are what we most think of when we think of joints. And no wonder! These are the ones present in all four of our limbs and they are the most common joints we have. They’re the joints that let us rotate our shoulders and hips, and bend our elbows and knees without pain. Just one or two cool things about them:

1. The main component that gives synovial joints their magic is called “synovial fluid”. It gives a slippery, weight-bearing film that reduces friction both for our movement and inside the synovial joint itself. It also gives the surrounding cartilage nourishment and is made from filtration of blood’s plasma via the capillaries in the synovial membrane. Kewlio-beans!

2. But synovial joints aren’t always necessarily strong. For example, you’ll notice that the shoulder and fingers, two signature sites of synovial joints, are very easily and commonly dislocated, yes? This is because, for the most part, synovial joints are built for great flexibility and range of motion, rather than durability and power. But that’s where handy-dandy numbers of “reinforcing ligaments” come in to stabilize and make the joints strong!

And that’s all for now, loves! Muscle tissue and muscle system is coming up next! As usual, hope you enjoyed!