We spend a lot of time kicking around the office, discussing anatomy and fighting about which structures are the coolest. We all know how I feel about the pelvic girdle, but the thoracic cage comes in at a close second.
The thoracic cage is an interesting structure designed to protect some of the most important organs in your body. Keep reading to find out just how the thoracic cage is structured to make you keep on keepin' on!
1. The thoracic cage is conical in shape—narrow above and broad below. This is what helps give your upper body shape.
2. Run your hands down the back of your ribs. Can you feel the shape of the cage? It is relatively flat; the anterior part of the cage is noticeably curved to accommodate organs within it.
3. If you look at the cage in the transverse inferior, you will notice it is shaped somewhat like a kidney.
4. Its kidney-like shape is ideal for protecting the heart and lungs. Look how neatly they fit inside.
5. The costal cartilage are fibrous tissues that allow for the expansion of the thoracic cage. When air comes into the lungs, the lungs inflate and the thoracic cage expands to accommodate them.
6. The 12 ribs that form the cage are uniquely shaped. Most have a head (articulates with the bodies of the vertebrae), a neck (flattened section of bone), and a shaft (serves as the attachment site for several muscles).
7. The shape of the head is ideal for articulating with the vertebrae.
Explore the thoracic cage.
Watch the video to see the thoracic cage from all angles and explore a rib!
Want to see more?
Subscribe to our newsletter for product updates, sales, and free content. You'll automatically be entered to win a free Visible Body download product of your choice!
Related Posts
- 3D Skeletal System: Atlas, Axis, and the Atlanto-Axial Relationship
- 3D Skeletal System: Function of the Sphenoid
- 3D Skeletal System: The Pelvic Girdle
Sources:
- Skeleton Premium
- Gray's Anatomy -- The Thorax
Think of how many things you do during the day; you stretch first thing in the morning, lift your coffee cup, wave at people, type, write, text, play Angry Birds—no matter what it is you do, chances are you're using your arms to do them. And you know what's incredible about that? You wouldn't be able to use your arms without the shoulder girdle!
I'm fascinated by the shoulder girdle, to be honest. It's such an interesting structure and presents an even more interesting joint. Let's take a quick look, shall we?
As always, if you own
Skeleton Premium 2, feel free to follow along!
Bones of the Shoulder Girdle
The shoulder girdle is made up of two posterior scapulae and two anterior clavicles. These bones make an incomplete ring around the upper thoracic cage. The medial end of each clavicle articulates with the manubrium and scapulae; each scapula connects to the thoracic cage by muscle only. How crazy is that? The only thing that connects the upper limbs and the scapula to the axial skeleton are the
clavicles. That's a pretty big job, wouldn't you say?
The scapulae are flat, triangular bones that serve as the attachment sites of many muscles, including the deltoids. Muscles of the back and thorax connect the scapulae to the thoracic cage.
Here's a quick run-down of the girdle's articulations:
|
|
Articulations
|
|
Scapula
|
Humerus, clavicle
|
|
Clavicle
|
Scapula, manubrium, cartilage of the first rib
|
Glenoid Cavity and the Shoulder Joint
Hold one of your arms out and rotate it. Your arms have more motility than your legs, despite the fact that the shoulder and hip joints are the same type of joint!
Each scapula has a concave, articular surface called the glenoid cavity (or glenoid fossa), which articulates with the head of the humerus. The cavity is covered with cartilage. The ball-like head of the humerus articulates with the glenoid cavity, creating a ball-and-socket joint that allows the upper limb great motility. A
capsular ligament is part of the articular capsule that surrounds a synovial joint (freely moving joint); capsular ligaments reinforce joints and provide stability. The capsular ligament of the shoulder joint provides more motility than the hip joint—in fact, it allows the scapula and the humerus to separate more than 2.5 cm, which means your upper limbs have a fantastic range of motion!
Watch the range of motion of a ball-and-socket joint here:
Landmarks of the Scapula
The scapula is such an interesting bone. I mean, look at it! It's such a cool shape that it's also known as the
shoulder blade. You are walking around with two knives permanently strapped to your back. How awesome is that?
Landmarks, or characteristics of the bone, have different functions: muscle attachment sites, bone and ligament articulation sites, passage for nerves and vessels, and more. In the image, all bone landmarks are highlighted in different colors (a nifty tool in
Skeleton Premium 2).
For example, the acromion and the coracoid process (in light pinkish purple) are the two major projections of the scapula. The acromion is an oblong process that hangs over the glenoid cavity, while the coracoid process is a thick, curved process that runs almost parallel to the acromion. They are connected by the coracoacromial ligament. This ligament supports proper movement of the joint by arching over the superior portion of the shoulder, protecting it.
The scapular spine (in pale orange-red) is a prominent plate of bone that serves as the attachment site for portions of the trapezius and the deltoid. At the distal end of the spine is the acromion.
Want to see more?
Sign up for our newsletter and get information about sales, product upgrades, and free content!
Related Posts:
- 3D Skeletal System: The Pelvic Girdle
- 3D Skeletal System: Compact Bone, Spongy Bone, and Osteons -- Oh My!
Sources:
- Skeleton Premium 2
- Gray's Anatomy (The Acromioclavicular Articulation)
Your skeleton's awesome—no bones about it!
I couldn't resist.
The point still stands! Your skeleton is an incredible structure. It gives your body shape, it protects vital organs, and it's alive. That's right! When you think of the skeleton, what comes to mind? Hard, dry bones, right? You can thank artistic conditioning in kindergarten for that one. The thing is, bones may be hard on the outside, but on the inside they're a smorgasbord of vessels, nerves, and other things. I may just blow your mind with this post.
Compact Bone (cortical bone)
Compact bone is dense bone tissue found on the outside of a bone. Basically, in kindergarten when you drew skeletons, you were drawing compact bone. Compact bone is enclosed, except where it's covered by articular cartilage, and is covered by the periosteum. The periosteum is a thick fibrous membrane covering the entire surface of a bone and serving as an attachment for muscles and tendons. Vessels pass from the periosteum through pores into the compact bone and run through canals found throughout the tissue.
Spongy Bone (cancellous bone)
"Cancellous" makes it sound so negative, doesn't it? Spongy bone is on the interior of a bone and consists of slender fibers and lamellae—layers of bony tissue—that join to form a reticular structure. Spongy bone is supplied by fewer and larger vessels than compact bone. These vessels perforate the outer compact layer and are distributed into the spongy portion of bone, which is filled with marrow. Bone marrow is tissue found in long bones, like the femur, that contains stem cells.
Osteons (Haversian system)
Osteons are interesting little things. Osteons are structural units of compact bone. Each osteon consists of a central canal, which contains nerve filaments and one or two blood vessels, surrounded by lamellae. Lacunae, small chambers containing osteocytes, are arranged concentrically around the central canal.
Femur Bone
Bone marrow fills the cavities of long bones and occupies the spaces of spongy bone. Yellow marrow, consisting mostly of fat, is found in the central cavities of long bones. Red marrow is found in the medullary cavities of flat and short bones, articular ends of long bones, vertebral bodies, spongy bone of the cranium, sternum, ribs, and scapulae.
The femur is famous for being the longest bone in the body, as well as one of the strongest. Your femurs support a great deal of weight—your entire upper body, in fact! The femur is also known for its marrow-filled medullary cavity, which is present in all of the long bones of the limbs. The sternum and hip bone are the sites from which marrow is usually extracted, however the femur is also used.
Bone marrow biopsies are done usually to determine or diagnose certain conditions, such as leukemia, anemia, abnormal number of white blood cells, and whether cancer has spread to the bones.
Bone Marrow and Stem Cells
You've been bombarded by headlines about stem cells over the past decade, but what do they actually do? Well, stem cells can become red blood cells (which provide oxygen to tissue), white blood cells (which fight infections), or platelets (which help in blood clotting). They have the potential to become specialized cells, which can help in treating certain diseases.
Osteoporosis
I drink seven or eight thousand glasses of milk a day. I love it, and my love for it helps protect me against osteoporosis. I'm sure you've seen dozens of ads telling you to drink milk or take vitamins to supplement bone health (Sally Field does one), but they never quite explain what osteoporosis is.
Osteoporosis is a disorder, more common with increased age, in which bone tissue becomes thinner, resulting in brittle bones that are more susceptible to breaking. Sex hormones are particularly important in stimulating bone cell growth; after middle age, these hormones decrease in production, which means bone cell growth decreases. Bones become noticeably thinner, especially for women after menopause when estrogen levels are very low.
Compact bone becomes more brittle, particularly in the long bones, which is why breaks and fractures in the tibia and femur are things to keep note of when diagnosed with osteoporosis. The femur and tibia already bear the weight of most of the body; small accidents, like simple falls, can result in injury. In spongy bone, trabeculae—small struts that are separated by cavities filled with marrow—become thinner and the spaces between them become wider, causing an overall weakening of bone structure.
Milk is rich in calcium and vitamin D, the two most important nutrients for bone health. About 99% of the calcium in our bodies is in our bones and teeth. Our bodies require vitamin D to absorb calcium. So the next time you're watching TV and Sally Field tells you that you need to eat things rich in calcium and vitamin D, you should listen. You should listen to her anyway, because she's awesome.
Want to see more?
Download our free eBook about the sphenoid! It's just as cool as the pelvic girdle—and it's shaped like the Bat symbol!
Related Posts
- 3D Skeletal System: Atlas, Axis, and the Atlanto-Axial Relationship
- 3D Skeletal System: Function of the Sphenoid
Sources
- Skeletal Premium 2
- National Osteoporosis Foundation
- Kid's Health: Aspiration and Biopsy
I must put my hand on my hip at least a thousand times a day. I don't know what it is—it's a habit that I can't seem to break. Mostly, I think it's because I never quite know what to do with my hands if I'm just standing. But there's something to be said for resting your hand on something sturdy—even when the sturdy thing is you!
The pelvic girdle may look like one giant bone, but it's actually made of three. The pelvic girdle connects the bones of the lower limbs to the axial skeleton by different attachment sites, and supports the vertebral column.
And I'm going to be honest: I find the pelvic girdle to be one of the most beautiful structures in the entire body. I mean, look at it!
Okay, let's take a look at the pelvic girdle, its relationship with the femur, and its responsibilities in the body.
Bones of the Pelvic Girdle
When we're born, we have over 300 bones. As we grow, some bones fuse together, leaving us with 206 by the time we're adults. The pelvic girdle, as I said above, is made up of three fused bones: the ischium, the ilium, and the pubis.
The pubis forms the anterior part of the pelvic girdle. It is a flattened, irregular-shaped bone that articulates with the pubic symphysis, a cartilaginous joint.
The ilium is the largest and most recognizable part of the pelvis: it looks like the top of a wing. If your hip bones "stick out" (are visible through your skin), it's usually the ilium you're seeing; they protrude outwards. The ilium articulates with the sacrum, forming the posterior wall of the pelvic cavity. The iliac crest, the superior-most area of bone, is the attachment site for several muscles, including the latissimus dorsi and gluteus maximus.
The ischium, located directly below the pubis, forms the bottom of the "wing." Together with the pubis, the ischium forms the obturator canal, the large hole in the bone. The obturator canal is the attachment site for the obturator muscles, as well as nerves and blood vessels.
Acetabulum and the Pelvic Girdle
The femur and the pelvic girdle have a very special relationship—it's special in that it allows you to walk. Take a look at the femur (see image). The helmet-like structure highlighted in gold is the head. Many bones have a head. What's special about this particular head is its role as the ball in the ball-and-socket hip joint.
The pubis, ischium, and ilium have a hand in creating the acetabulum, the deep, hemispherical, cup-shaped depression (the socket) with which the head of the femur articulates. The head of the femur fits perfectly in this cavity; its ball shape allows it to roll the femur, rotating it in a way that facilitates walking. Ligaments hold the bones together.
For a better idea of how a ball-and-socket joint works, take a look at this quick video.
Male and Female Pelvic Girdle
In addition to supporting the vertebral column and allowing you to walk, the pelvic girdle—along with the sacrum and the coccyx—forms the walls of the pelvic cavity, which contains and protects some of the reproductive, digestive, and urinary organs.
The pelvic girdle is delicate and shallower in the female pelvis than the male—the ilia are less sloped, and the superior aperture is more circular.
Want to learn more?
Download our free eBook about the sphenoid! It's just as cool as the pelvic girdle—and it's shaped like the Bat symbol!
Related Posts
- 3D Skeletal System: Atlas, Axis, and the Atlanto-Axial Relationship
- 3D Skeletal System: Function of the Sphenoid
Sources
- Skeletal Premium 2
- Gray's Anatomy
In my previous bone post, I talked about how much I loved the sphenoid and its Batman symbol-esque shape. That still holds true. Coming in at a close second is the ethmoid. Once, someone asked me to describe the shape of the ethmoid bone, and the only thing I could come up with was "hot mess." Look at it—how else would you describe it?
The ethmoid (sphenoid, ethmoid—brain bone names are so cool) is an interesting little bone with some very important functions. Let's take a look!
(And, as always, if you have Skeleton Premium 2, feel free to follow along!)
1. The Ethmoid Articulates with 13 Bones
Talk about being the belle of the ball! The ethmoid articulates with more than half of the bones in the skull: the frontal bone, sphenoid bone, nasal bones, maxillae, lacrimal bones, palatine bones, inferior conchae, and the vomer.
2. The Ethmoid Helps Form the Orbits and Nasal Cavities
It's pretty much impossible to feel where the ethmoid is in the skull; it sits at the roof of the nose and helps form the inner portions of the orbits (eye sockets). The middle conchae, located beneath the cribiform plate, form part of the lateral walls of the nasal cavities. The orbital plates help form the interior of the orbits.
3. Cool Structures Attach to the Ethmoid
At the top of the ethmoid is a long, thin triangular process called the crista galli. This projection of bone serves as the attachment site of the falx cerebri. The falx cerebri is the larger of the two folds of dura mater separating the two hemispheres of the brain that lies between the cerebral hemispheres and contains the sagittal sinuses.
(Check out our sweet coronal cross-section!)
4. The Ethmoid Contributes To Your Sense of Smell
The olfactory bulb, which transmits smell information to the brain, rests on top of and is protected by the cribiform plate. As you can see in the picture, the plate is perforated by numerous foramina, which give passage to the branches of the olfactory nerves.
(Look at that awesome sagittal cross-section! We're pulling out all the stops.)
5. The Labyrinths of the Ethmoid (do not contain a minotaur)
The labyrinths of the ethmoid contain several ethmoidal sinuses. These sinuses are composed of air cells that receive sensory information from the ethmoidal nerves. The sinuses drain into the nasal meatuses.
WANT TO LEARN MORE?
Download our free eBook about the sphenoid! It's just as cool as the ethmoid—and it's shaped like the Bat symbol!
RELATED POSTS
- 3D Skeletal System: Atlas, Axis, and the Atlanto-Axial Relationship
- 3D Skeletal System: Function of the Sphenoid
Sources:
- Skeleton Premium 2
- Merriam-Webster Dictionary (Falx cerebri)
- Chico State University, CA, Anthropology Dept.
There are 33 vertebrae in your vertebral column. Or is it 24? Doesn't matter—both
numbers are correct. You're born with 33, but the sacrum and coccyx fuse to the rest of the spine, making it 24 by the time you're an adult.
Of those 24 (not counting the sacrum and coccyx), two vertebrae are fortunate enough to have names. The atlas (C01) and axis (C02) are two of the most important vertebrae in the spine. Without them, head and neck movement would be impossible.
The atlas and axis vertebrae are the two most superior bones in the vertebral column. They are part of the seven cervical vertebrae. The atlas is the top-most bone, sitting just below the skull; it is followed by the axis. Together, they support the skull, facilitate neck movement, and protect the spinal cord. (Think of them as BFFs—you won't find one without the other.)
Unlike the other vertebrae, the atlas does not have a spinous process. Instead, it is ringlike and consists of an anterior and posterior arch, as well as two lateral masses. The transverse processes (the protrusions of bone on either side of the ring) serve as the attachment sites of muscles that assist in rotating the head. The foramina (the holes) give passage to the vertebral artery and vertebral vein.
The axis is somewhat analogous to the other cervical vertebrae in shape, but it differs
slightly for two reasons: its spinous process isn't as obviously bifid, and the presence of the dens. The spinous process serves as the attachment site for many muscles of the spine, particularly those close to the skull, as well as the nuchal ligament.
The dens, or odontoid process, is a toothlike projection of bone that rises perpendicularly from the upper surface of the body of the axis. Its purpose is very important, but I'll get to that later.
Let's talk about joints.
CRANIOVERTEBRAL JOINTS
There are many types of vertebral joints, but the atlas and axis form the only craniovertebral joints in the body. A craniovertebral joint is exactly what it sounds like: a joint that permits movement between the vertebral column and the skull.
The ligaments in the spine support and reinforce the joints between the vertebrae. The atlas and axis in particular work with the ligaments to move the neck. The atlas and the occipital bone form the atlanto-occipital joint, which allows neck flexion. When you nod your head as if to say "yes," that is neck flexion. The atlas and axis form the atlanto-axial joint, which allows head rotation. If you shake your head as if to say "no," that is head rotation.
The atlanto-axial joint is a compound synovial joint. A synovial joint is a freely moveable joint, differing from other types of joints due to the presence of synovial fluid, which lubricates the joint. Most of the main joints (hands, feet, and other regions in the appendicular skeleton) are synovial joints.
It is also a pivot joint. A pivot joint is made by the end of one articulating bone rotating in a ring formed by another bone and its ligaments. Think of a metal washer twisting around a bolt. The dens articulates with the facet on the atlas, as well as the transverse ligament, and this articulation provides the head with approximately 50% of its movement.
LEARN MORE ABOUT THE SKELETON
Preview Skeleton Premium 2. Now available for iPad, PC, and Mac.
The human skeletal system has over 200 bones, and those bones have over 800 bony landmarks. Bet you never guessed that your bones were so complex. Haven't you learned by now that every part of your body is ridiculously awesome?
We took those 200+ bones and 800+ landmarks and packed them all into our newest app: Skeleton Premium 2 for iPad. We’ve also included some cool new content on synovial joints, bone tissues, and skeletal system pathologies. But wait, there's more! There's also a big section of quizzes!
Pretty awesome, right? Well, guess what? I'm going to give you a sneak peek of the app (it's not published just yet!). I'm going to use just one section of the app (the bone region section) for you to learn some basic facts about the maxilla bone and its landmarks.
No need to thank me.
Skeleton Premium 2
Here is a quick preview of what is in the app:
* True 3D models of bones and ligaments in a complete skeleton that can be rotated and zoomed to study details.
* Over 800 bony landmarks and regions illustrated in color. Additional information for each landmark includes its pronunciation and table data that lists attachments, articulations, locations, and nerve and vascular passage.
* More than 200 preset views that present individual landmarks on each bone and articulations and ligaments by skeletal regions.
* 3D moving models of synovial joints
* A gallery of animations and illustrations that show bone tissue, pathologies, and regional anatomy
* A quiz bank with over 500 questions
MAXILLA IN THE FACIAL SKELETON
So, you open up the app and the first thing you see is a menu (the one in the image above). Pretend you have the app in front of you. Select Region Views, which brings up a bunch of tabs and thumbnails (below). Each tab contains preset views organized by five body regions. (You can edit these views any way you want by rotating, zooming in and out of, adding or removing structures. The views provide an easy place to start.)
Tap the Skull tab, then choose the 21. Maxilla, Context view.
That action launches a preset view that shows where the maxillae are in the skull (above). Using my finger (like a pen stylus), I can drag it to rotate the model for a superior view. To get a really good one, I'd eliminate the frontal and parietal bones (below). Notice that from this angle the maxillae seem to flank the nasal cavity.
How do the maxillae contribute to the nasal cavity? To figure it out I can take the model, remove all the bones that aren't part of the facial skeleton, and turn it around to get a posterior view (below, right).
Now, isn't that a cool view? See how the maxillae help form the nasal cavity? This view also shows that a part of the maxillae form the hard palate. To get a better view of that, I can hide everything except the maxillae (and teeth) and rotate the model for an inferior view (above, left).
To bring the original view (a.k.a. the starting point) back, I can reset the view by tapping on its name in the top left corner (21. Maxilla in Context). To get a definition, I can click the Definition button across the bottom.
MAXILLA BONE LANDMARKS
While the context is interesting, what about the bone itself? By clicking on the Explore This Bone button, we can take a deep dive into the bone landmarks of the maxilla. Once you click it, a model of the maxilla in isolation appears, along with a key that designates 13 landmarks on the bone. By tapping different parts of the bone, I can see the names and locations of the various landmarks.
To differentiate between the landmarks, I can turn on a color-coded map to make them visible and distinct. (That's what I did below. In the following four pictures I also selected the button that hides all the UI elements. I did that just to focus in on the bone for a moment.)
-resized-600.png)
I can rotate the bone 360 degrees and tilt it so I can get a view from any angle. Check out the above images. I can see the maxilla from an anterior view (above, left) to lateral views (above, right and below, left), to an inferior view (below, right).
Look at that last picture (above, right). See the green outline? The green designates the alveolar process, which articulates with the teeth. The cavities (shown in blue) are the alveolar canals.
Okay, while clicking around the veritable rainbow of landmarks, say I wanted to learn some stuff about those cavities. So, I call up the landmark information and get down to business.
The alveolar canals (cavities for teeth) are highlighted. These canals provide passage to the superior alveolar vessels and posterior alveolar nerves.
Directly above the canals is the maxillary tuberosity. It's where the pyramidal process of the palatine bone and the lateral pterygoid of the sphenoid articulate with the maxilla. It's also where the medial pterygoid muscle attaches (the muscle that draws the mandible forward).
At the beginning of this post, I mentioned the hard palate. Well, here it is! It too provides passage to nerves and vasculature.
MAXILLA QUIZ
Last but not least, a visual quiz. Can you point to the alveolar process in the image above (without looking at the preceding images and text, you bunch of cheaters!)?
If you guessed the green outline around the alveolar canals, you're right! Good job.
So, what do you think? Pretty nifty, right? Leave your feedback in the comments section!
To be notified of product updates, free content, and to be entered to win a free PC or Mac download product of your choice, sign up to receive our newsletter. You know you want to.
Put your hands on your chest and take a deep breath. Feel how your chest expands? That's your thoracic cage—or rib cage, as it's more commonly known—pressing up against your hands. Without the thoracic cage, some of your body's most important organs would be unprotected, and your torso would be completely without shape. Imagine walking around with your lungs somewhere near your stomach and your shoulder girdle collapsing into itself. Not a pretty thought.
The thoracic cage, a flexible framework of bones and cartilage, is conical in shape. It is narrower at the top and broadens to fit and protect some critical organs of respiration and circulation—that is, the lungs and heart. The thoracic cage gives your upper torso structure. Women have smaller cages than men; the capacity is less, and the sternum is shorter and higher.
Note the anterior view of the thoracic cage above: The front of the thoracic cage includes seven pairs of vertebrosternal ribs (true ribs), which articulate with the sternum, an elongated flattened bone. There are also three pairs of vertebrochondral ribs (false ribs)—each false rib attaches to the cartilage of the rib directly above it.
Take a posterior look at the thoracic cage and you’ll find another two pairs of ribs; these are the vertebral ribs (floating ribs). Posteriorly, all 24 ribs articulate with vertebrae of the thoracic portion of the vertebral column.
Like anything else in the body, the ribs that make up the thoracic cage aren't blank curves of bone. The ribs are complex in their own right. Let's take a look!
ANATOMY OF A VERTEBROSTERNAL RIB
The true ribs, false ribs, and floating ribs all have a head, neck, and shaft. All the ribs of the thoracic cage articulate with vertebrae and each has a costal groove for passage of the intercostal vessels and nerve. Looking at the 24 ribs together you might tend to think that the ribs differ only in size. But they differ in shape too. For the sake of expediency let’s look at the particular bony landmarks on the seventh vertebrosternal rib (the 7th true rib). It helps form the first section of the cage.
|
Landmark
|
Characteristics
|
|
Shaft
|
The longest part of the bone; gives attachment to the intercostals, the external oblique, the iliocostalis lumborum and thoracics, levatores costarum muscles, and the serratus anterior
|
|
Tubercle
|
Eminence that articulates with the transverse process of T07
|
|
Neck
|
Attachment site for the anterior costotransverse ligament
|
|
Head
|
Articulates with the bodies of T06 and T07, and acts as the attachment site for the interarticular ligament
|
|
Costal cartilage
|
Cartilage that allows the ribs to move; attachment site for diaphragm, pectoralis major, rectus abdominis, and transversus thoracis
|
|
Costal groove
|
A groove on the inner part of the bone, through which the intercostal nerves and vessels pass
|
THORACIC CAGE ANOMALIES
Cervical Rib
While most of us are born with 12 sets of ribs, it's not uncommon to have a normal variance or two. There is a chance, dear reader, that you may have more than the normal number of ribs. Crazy, right? Supernumerary ribs can be a harmless variant in most cases, but in some it can cause issues.
A cervical rib is a normal variant. A cervical rib is a congenital disorder in which one extra rib arises before the first normal set of ribs (01). It is small and is often called a "neck rib" due to its location. A cervical rib is present in only 0.5% of the population and is more common in females than in males. In rarer cases, an individual can present an extra set of cervical ribs.
A cervical rib is usually asymptomatic, but in some cases it can cause thoracic outlet syndrome by compressing the brachial plexus or subclavian vessels. Symptoms include pain almost always, as well as discoloration of the hands, weakness of the hand or arm, and stiffness.
Short Rib
A short rib is not a clinically significant variant, and is thus named for when a mid-thoracic rib arch is shorter than it should be through no fault of trauma or surgery. A short rib occurs in approximately 16% of the population, and out of those instances, only 8% occur on the right side.
Funnel Chest
In contrast, pectus excavatum or funnel chest is a depression of the sternum, which causes the skin to be concave. In some cases, funnel chest is a cosmetic issue, but in others it can lead to impaired breathing, heart displacement, decreased heart density, and chest pain.
Now I want you to put your hands back on your chest and take a deep breath. Feel the 12 sets of bone expand against your fingers. If you ever get stuck on what it is your thoracic cage does, think of it as your body's police force: it shapes and protects.
Want to review more about bony landmarks in the thoracic cage? Sign up to get information about our upcoming Visible Body Skeleton Premium 2. It’s an app that includes a comprehensive human anatomy skeleton model with tons of content on bony landmarks, joints, bone tissue, and common bone pathologies.
Sources:
Kurihara, Y. et al (1999). The ribs: Anatomic and radiologic considerations. Manuscript submitted for publication, Department of Radiology, St Marianna University School of Medicine, Kawasaki City, Kangawa, Japan.
Freyschmidt, J., Brossman, J., Wiens, J., & Sternberg, A. (2002). Koehler/zimmer's borderlands of normal and early pathological findings in skeletal radiography. (5th ed.). Germany: Thieme.
The sphenoid. Aside from having the most sci-fi name in all existence, it's pretty much the
coolest-looking bone in the body. Best yet? It's in your skull. Bet you never thought you've been walking around all this time with a bat-shaped bone in your head.
The sphenoid is an interesting bone in that while it doesn't actively protect the brain like the bones of the calvaria, it does have a multitude of functions, particularly in creating tunnels through which various nerves pass.
IMPORTANCE OF THE SPHENOID
There are 22 bones that make up the skull, and the sphenoid (don't you just love saying it?) is one of the 8 bones of the neurocranium. It is situated at the base of the skull, acting as the keystone. A keystone in architecture is the piece at the apex of an arch; it locks all the other pieces together and bears the weight. And just like a keystone holds everything together in an archway, so does the sphenoid in the skull.
The sphenoid articulates with 12 bones:
- frontal
- occipital
- parietals
- temporals
- zygomatics
- ethmoid
- vomer
- palatines
Of these 12 bones, 10 belong to the neurocranium. In my previous post, I discussed the neurocranium's role in protecting the brain. While it is part of the neurocranium, the sphenoid does little in the way of protection. It serves more as a base for the skull.
SPHENOID LANDMARKS
Our bat-shaped sphenoid is divided into a median body, two greater wings, two lesser wings, and two pterygoid plates.
Think of the body of the sphenoid as the body of the bat it's shaped like: it is from the
body that the wings and processes project. It is cubical in shape. It also has two hollowed-out, air-filled cavities—the sphenoidal sinuses. There are four pairs of sinuses, and like the others the sphenoidal sinuses have two jobs: to help lighten the weight of the skull, and to give each person's voice individual character.
There is also a deep depression in the superior surface of the bone called the sella turcica, or "Turkish saddle." It is so named because of its resemblance to the saddles Turks used to use, with supports in the front and back. It is in this depression that the pituitary gland sits.
The greater and lesser wings are processes of bone that extend outward. The greater wings are perforated by various foramen, the most obvious being the large superior orbital fissures, which are formed by both sets of wings. Various structures pass through the fissures, including the oculomotor nerve (III); the trochlear nerve (IV); the lacrimal, frontal, and nasocillary branches of the ophthalmic nerve (V); and divisions of the ophthalmic vein. The greater wings also serve as the attachment site for the temporalis muscles.
The lesser wings and the body of the sphenoid form the optic canal. It is through this canal that the optic nerve (II) passes from the brain to the eyes.
The lateral and medial processes project downward from the body of the bone, like legs. It is to the lateral processes that the lateral and medial pterygoid muscles attach. The sphenoidal processes of the palatine and the ala of the vomer articulate with the medial processes.
PATHOLOGIES OF THE SPHENOID
The thing about the sphenoid is that it's located in such a place that injuries to it are not as common as injuries to bones at the forefront of the skull. That said, you can definitely injure it. Fracturing the bone following severe bumps, impacts, and whiplash can affect vision or cause nerve damage.
One of the more common pathologies is sphenoid sinusitis. Sinusitis is an inflammation of the mucous membranes of sinus cavities. Symptoms include headache, facial pain, and infected nasal drainage, as well as nerve irritation.
Sometimes, sinusitis can become very severe and complications, such as recesses (small cavities), can arise, or other issues can form in the sinuses (such as a tumor), prompting the need for a sphenoidotomy. A sphenoidotomy is, quite simply, the surgical procedure of cutting into the sphenoid sinus, with the most common approaches through the nasal cavity or nasal septum. A sphenoidectomy is when part of the sphenoid is removed, usually in instances involving tumors.
Hard to believe so much is associated with your bat bone, huh? The sphenoid, like all bones in the body, is a wellspring of information and serves a slew of purposes. Regardless of its importance, it is still—without a doubt—the coolest-looking bone you have.
Want to review more about the sphenoid? Check out our mini ebook! It includes dozens of images from our upcoming app that includes a comprehensive human anatomy skeleton model with tons of content on bony landmarks, joints, bone tissue, and common bone pathologies.
Sources:
Rimal, D., Hashmi, S., & Prinsley, P. (2006). An unusual presentation of sphenoid sinusitis with septicaemia in a healthy young adult. Emergency Medicine Journal, 23(36), doi: 10.1136/emj.2005.033340
Schaefer, MD, S. (2012). Sphenoidotomy. In Retrieved from http://www.nyee.edu/ent_rss_sts_sphenoid01.html
Take your hand, make a fist, and tap your head. You know that you’re rapping your knuckles against your skull, but did you know that if your skull weren’t there your
knuckles would most likely get stuck in brain matter? Yep. You’ve seen pictures of the human brain: a pinkish-gray structure that looks like the inside of a walnut. However, your brain isn’t thick or sturdy—it has the consistency of gelatin! This is why your skull is so important: it not only gives your head shape, but it protects your brain.
The Neurocranium
The 22 irregular bones that make up the human skull are divided into two groups: those that form the neurocranium, and those that form the facial skeleton. The neurocranium (braincase) is comprised of 8 bones, while the facial skeleton is made up of 14 bones. If you press down on any part of your face (with the exception of your lips), you will feel the bone that gives it shape. However, if you touch any part of the top, back, or sides of your head, you will feel the bone that protects that part of the brain.
For this particular topic, we’re going to be looking at the major components of the neurocranium and its roles as both a protector and villain to the brain. (We’ll save the facial skeleton for another day.)
The Calvaria
One of the biggest components of the neurocranium is the calvaria. The calvaria, or skull cap, is the upper part of the neurocranium and is comprised of 6 bones, all named for the lobes of the brain they protect—the frontal bone protects the frontal lobe, the occipital bone protects the occipital lobe, and so forth.
A quick break down of the calvaria:
|
Bones & Sutures
|
Role
|
|
Frontal
|
- Gives shape to the forehead, orbits, and nasal cavity (not part of the facial skeleton, though!)
- Articulates with 12 bones (10 from the facial skeleton)
|
|
Occipital
|
- Gives shape to the back of the skull
- Gives passage to the medulla oblongata
- The foramen magnum is the large opening in the bone where the spinal cord and brain meet
|
|
Parietal (right and left)
|
- Protect the parietal lobes
- Come together to form the sagittal suture
- Also form the coronal suture with the frontal bone
|
|
Temporal (right and left)
|
- Protect the temporal lobes
- Connect the structures of the inner and outer ears
- Pointed styloid processes are the attachment sites for the muscles of the tongue and neck
|
|
Cranial sutures
|
Fibrous joints where bones meet, found only in the skull; there are 17 total
|
In addition to the calvaria, there are two more bones that enclose the brain in the skull. The sphenoid is the keystone bone at the base of the neurocranium. It’s a spectacularly shaped bone (it looks like a bat!) that, in addition to containing the sphenoidal sinuses (air cells), has a deep depression that holds the pituitary gland. The other bone is the ethmoid, a spongy, cubed bone that gives shape to part of the roof of the nose and the orbits. The ethmoid is also home to numerous foramina through which the branches of the olfactory nerves pass.
Concussion
Each bone is around 7 mm thick, and the brain is suspended in cerebrospinal fluid with three layers of meninges separating it from the bones. But any contact-sport player will tell you that sometimes those natural barriers don’t matter at all. The thing is, despite how well your body tries to protect the brain, the world has many dangers. Your brain is susceptible to all sorts of trauma, with concussion the most common.
But what is a concussion, exactly?
As I said above, the brain has the consistency of gelatin (or soft tofu), and sometimes when you take a knock to the head the brain’s vanguards aren’t enough to keep the brain from being damaged. The brain will bypass the cerebrospinal fluid and the meninges and drag over the hard inner surface of the neurocranium. This can result in damage and interference with normal brain function. Take a look at the video below (no audio).
Symptoms of concussion can include loss of consciousness, amnesia, lethargy, drowsiness or difficulty waking up, confusion, feeling “spacey,” nausea, and headache. Severe symptoms include convulsions/seizures, coma, abnormal eye movement or uneven pupils, problems with walking, and repeated vomiting.
The scariest symptom can be no symptom at all. Sometimes the person who suffers a concussion has no idea as symptoms don’t present themselves, which can be incredibly dangerous. The most significant complications associated with concussion are brain swelling and increased intracranial pressure (ICP). This is why all head injuries need to be checked by a medical professional, even if you think you’re fine.*
So remember: when you play sports or are doing something that could result in a head injury, wear a helmet. The neurocranium can only do so much to protect the brain; we have to do our part too! To learn more about the bones that form the skull, check out our free mini e-book.
(*Seriously, don’t try to walk it off. Err on the side of caution and get it checked out.)
Heller, MDA, J. National Library of Medicine, (2012).Concussion (PMH0001802). http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001802/
Mayo Clinic Staff. (2011). Concussion (DS00320). http://www.mayoclinic.com/health/concussion/DS00320