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Learn Muscle Anatomy: Bursae

The other day, I let my ten-year old niece play with Muscle Premium on my phone (while I watched cartoons). She kept making the model spin—around and around and around, like a ballerina, until she abandoned it for the muscle actions.

"Auntie," she said, and then didn't follow up with anything, completely engrossed in Elbow Flexion. When I prompted her, she looked up at me and whispered, as if confessing a secret, "Is it supposed to hurt?"

I asked her what she meant. She pointed to the moving model.

"Do bones rub against each other like that all the time? Because I feel like it should hurt."

I watched the animation for a bit—the olecranon of the ulna slid against the humerus's olecranon fossa, back and forth, flexed in a continuous loop. It did look a bit like they were rubbing together. Actually, if there wasn't something there acting as a cushion, moving the joints would be incredibly painful. Luckily, we're not that bad off.

"It doesn't hurt," I began, settling back to finish The Legend of Korra, "Because you have little pillows called bursae inside you that stop your bones from rubbing like that."

She turned her attention back to the TV and waited until the end of the episode to ask more. (My niece is polite like that.)

That was an actual exchange between me and my niece Em, who has an affinity for all things science and interesting. She's awesome.

Anyway, what I told her was the truth: bursae prevent our bones and muscles, particularly in the joints, from rubbing together and creating painful friction. Imagine trying to bend your knee without something to cushion the movement. Talk about ouch, right?

Muscle patella superficial subcutaneous prepatellar bursa knee synovial resized 600 

See those purple lumps in the picture? Those are bursae. They live between bones and bones, or bones and muscles, or muscles and skin, serving to prevent friction at points of stress throughout the body. In the picture, you can see the bursae are either prominently displayed (on top of the patella) or partially hidden between bone and muscle. Think of how often you move and bend your knees—I'm doing it right now, and I'm just sitting! It would be a much more painful action without the bursae there to cushion things.

Bursae come in three packages: synovial, subcutaneous, and adventitious. 



Most of the bursae in the body are synovial: thin-walled sacs interposed between bones, muscles, and tendons. The lining of a bursa contains a capillary layer of synovial fluid, which provides two lubricated surfaces that enable freedom of movement. Synovial bursae tend to be located in your joints, like your knees, feet, and shoulders.

 Muscle bursae shoulder joint subacromial bursa synovial resized 600


There are also adventitious, or accidental, bursae. These occur in soft tissue over bony prominences, usually because of repeated pressure or shearing.

An example of an adventitious bursae is a bunion, which is a deformity of the big toe. Wearing ill-fitting shoes can sometimes force the big toe inward towards the other toes. The bursa at the metatarsophalangeal joint becomes swollen, but the biggest issue is the normal part of the head of the first metatarsal bone is tilting sideways and sticks out at its top. This creates a large bump or prominence.

 Muscle metatarsophalangeal bursa hallux big toe joint metatarsal resized 600

Subcutaneous bursae lie between the skin and a bony process, like the aforementioned olecranon of the elbow.

Muscle olecranon subcutaneous bursa elbow joint resized 600  


You've probably spent enough time on this blog to know what the suffix –itis means, so you won't be surprised when I say that bursitis is the inflammation of a bursa. When the bursae become inflamed, their gliding ability is lost, which can be painful. An inflamed bursa is usually the result of trauma, overuse, or infection. Even something as simple as lifting something heavy can bring it on.

The joints of the hips, elbows, and shoulders are normally the areas affected by bursitis, but it can occur anywhere (inflammation of the bursae in the knee is known as Washmaid's Knee).




Muscles, 3D muscles

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Zybright Guest Post: 5 Things To Know about the Heart and Blood Vessels

Zybright, Visible Body's sister company, is the maker of My Incredible Body, a best-selling anatomy app for kids and a Parents’ Choice Silver Honor Award Winner. We're giving them the floor for another guest blog post, because they're awesome and we adore them.

Take it away, Zybright!


If you have our app, all this content comes from the Circulation Tour section. If you don't, get the free trial! You can download it to your iPad/iPhoneAndroid, or Windows 8.1 device. 

5 things to know about the heart and blood vessels

1. Your heart is a hollow muscle that has four chambers filled with blood. Think of these chambers as rooms. When your heart beats, two of those chambers—the ventricles—squeeze, which shoots blood where it needs to go. Your right ventricle sends blood to the lungs to pump it full of oxygen, and your left ventricle sends that oxygen-rich blood to the rest of your body.

2. If your heart chambers are rooms, then your heart valves (highlighted below) are doors. They open to allow blood to go in and out, but shut to prevent it from backtracking.

My incredible body heart valves semilunar tricuspid mitral anatomy resized 600

Fun Fact: If the valves don't close completely, blood could leak backward. The heart would have to work even harder to make sure blood was getting to where it needed to go.

3. The atria (highlighted below) are temporary holding tanks for blood. Your left atrium holds the blood that's coming from your lungs, while your right atrium holds the blood that is returning from the rest of your body.

My incredible body heart atrium atria anatomy resized 600

4. Systemic veins and arteries are spread throughout your entire body and act like roadways for your blood. Systemic arteries send oxygen-rich blood from your heart to your organs and tissues, which gives them oxygen in order to function. Systemic veins take blood that has lost its oxygen back to the heart, where it will be sent to the lungs for a refuel.

Fun Fact: The aorta is the largest artery in your body and is roughly the size of a garden hose!

5. The pulmonary vessels (branching structures in the image below) in the lungs work a little differently than the systemic vessels—in that they work the opposite way! The pulmonary arteries carry blood that needs to be refueled with oxygen to the lungs, while the pulmonary veins carry freshly-fueled, oxygen-rich blood back to the heart.


My incredible body heart pulmonary arteries veins lungs anatomy resized 600

Fun Fact: Pulmonary comes from the Latin word pulmonarius, meaning "of the lungs." 


Did you and your kids enjoy these facts? Then keep busy with these free 30-minute activities!

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Zybright Guest Post: 5 Facts About The Brain and Nerves (for kids!)

Zybright, Visible Body's sister company, is the maker of My Incredible Body, an anatomy education app just for kids. To celebrate the fact that kids are out for summer, they've written a guest blog to keep them learning until September rolls around again. Take it away, Zybright!


School’s out! Want to keep kids learning? Here are 5 facts about the brain and nerves.

If you have our app, all this content comes from the Nervous System Tour section. If you don't, get the free trial! You can download it to your iPad/iPhone, Android, or Windows 8.1 device. 


Five facts to know about the brain and nerves.

1. The cerebrum is the largest part of your brain (I highlighted it in blue below). It helps you make decisions, talk, smell, taste, and remember. Fun fact: the machine Professor Xavier uses in X-men  to locate mutants is called “Cerebro,” which is a play on “cerebrum.”

Cerebrum brain nervous system resized 600

2. The cerebellum is a smaller part of the brain. If you’ve ever reached for a pen, it’s your cerebrum that moves your arm and hand. However, it’s your cerebellum that fine-tunes the muscle movement, closes your fingers over it on the first try, and moves it into position to begin writing with it. Fun fact: cerebellum means little brain.


3. All day and all night your brain sends and receives messages to and from your body about everything from breathing and digesting food to moving. Many messages pass through your brainstem (I highlighted it in blue) before they go through the nerves in the rest of your body.  Fun fact: messages can travel as fast as 268 mph!

Brain stem nerves messages nervous system resized 600

4. Some nerves control jobs that are happening all day without us thinking about it much (or at all). These autonomic nerves are in charge of jobs like keeping the heart beating and your stomach digesting!  Somatic nerves are in charge of voluntary tasks—things you tell your body to do, like smiling at a friend or jumping into a pool.


5. The spinal cord is often called the information superhighway of your body (Hey, guess what I did: it's highlighted in blue below). That’s because almost all the messages sent between your brain and your body travel though this cord, which is only about as thick as a finger. 

Spinal cord nerves nervous system resized 600

Did you and your kids enjoy these facts? Then keep busy with these free 30-minute activities!

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Learn Muscle Anatomy: Muscles of Mastication

Learn Muscle Anatomy: Mastication

You know what I really enjoy? Eating.

Not just food itself, but the actual act of chewing something. Gum, steak tips, cake, one of those ginormous blueberry muffins from from the donut shop up the street—anything, really. I love working the muscles in my jaw in the act of mastication, or to reduce something to a pulp by crushing or kneading it with my teeth. There's something immensely satisfying about it.

Whenever you see a description of chewing or eating, it's always the jaw that's mentioned. While the jaw and your teeth are incredibly important in crushing food into a bolus, none of it would even happen—your mouth wouldn't even open—without the help of the muscles of mastication.


Deep Muscles of Mastication

I'm going to work from the inside out. The muscles of deep mastication are few, but powerful. There are only two of them: the deep masseter and the temporalis. These muscles, while "deep," are actually among the most "visible" of the mastication group, in that they aren't completely hidden by bone.


Deep masseter temporalis mastication muscles










Deep masseter

Zygomatic arch


Raises mandible against the maxillae with great force

Trigeminal nerve (V), mandibular branch (V3)


Temporal fossa and temporal fascia

Coronoid process and anterior ramus of the mandible

Elevates and retracts the mandible against the maxillae with great force

Trigeminal nerve (V), mandibular branch

Mandible elevation involves both muscles working to bring the mandible back up toward the maxillae. Remember, when you chew, it's only your jaw that moves; the maxillae remain fixed to the skull. The mandible is the only free-moving bone in the skull.

Mandible elevation temporalis deep masseter chewing mastication

Superficial Muscles of Mastication

The superficial muscles group is comprised of three muscles: the medial pterygoid, lateral pterygoid (superior and inferior heads), and superficial masseter.

Superficial mastication muscles lateral pterygoid head

The medial pterygoid and superficial masseter are pretty straightforward, but the lateral pterygoid is an interesting little thing. It is one muscle but originates in two different locations. There are other muscles in the body that have two different origins, such as the biceps brachii, but the lateral pterygoid is the only one in the head region.







Superficial masseter

Zygomatic bone

Ramus of the mandible

Raises the mandible against the maxillae with great force

Trigeminal nerve (V), mandibular branch (V3)

Medial pterygoid

Lateral pterygoid plate and the pyramidal process of the palatine

Ramus and angle of the mandible via a strong tendinous lamina

Assists the lateral pterygoid; draws the mandible forward

Trigeminal nerve (V), mandibular branch

Lateral pterygoid

Two heads: the superior from the sphenoid and infratemporal crest; the inferior from the lateral pterygoid plate

Condyle of the mandible and front margin of the articular disk of the temporomandibular articulation

Draws the mandibular condyle and articular disc forward

Trigeminal nerve (V), mandibular branch

Have you ever thrust your jaw out so your bottom teeth stick out in order to look like a bulldog? It's a face my youngest niece loves to make. Besides being hilarious on her little face, it's also a muscle action called mandible protraction, and all the superficial muscles of mastication are involved.

Mandible protraction superficial mastication muscles












Protraction (on the left) is the act of protrusion, or extending beyond the normal position. The opposing action is called retraction (on the right).


Temporomandibular Joint Dysfunction

Fun fact: I have TMJ. Well, we all have TMJ—the temporomandibular joint, that is. TMJ (and TMD, interchangeably) has also become an umbrella term for jaw and muscle pain.

When I was in high school, I used to go through a pack of gum every day. I would chew and chew and chew and chew until, finally, my mastication muscles gave up the ghost and began exhibiting pretty awful pain, followed by extremely limited jaw movement (I couldn't open my mouth properly for a while). Soon after, the articular disc floated out from between the fossa and condyle, causing my jaw joint to "click." While the muscle pain has long since abated, the clicking and popping of my jaw continues today.

Temporomandibular joint pain tmj tmd mastication muscles articular disc


















Temporomandibular joint dysfunction is the term used to describe pain arising from the temporomandibular joint and mastication muscles. It's an incredibly common ailment—anywhere from 20% to 30% of the population has it—and not very well understood, because not one thing causes it. TMD can be categorized by symptom, cause, and/or how long one has had it, and it is treated in a variety of ways, ranging from relaxation techniques to surgery (in extreme cases).

My best advice is to ease up on excessive gum chewing.


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Anatomy and Physiology Vocab: Medical Suffixes

While anatomy & physiology courses tend to be all about biology, anatomy, and other body-related science, there's a smidgen of them dedicated to language. The words used in the medical world all have their specific meanings, and even broken down into their most basic components they still have meaning.

Suffixes are pretty amazing. They have the power to change the meaning of one word into something else entirely.

Dermatology suffix medical ap vocab 1

Bam. A whole new word, just by adding a little bit at the end. Like I said: amazing.

There are quite a few suffixes in the medical world and it can be a task to remember them all. To help you, I've got some of the most common ones right here!













Tumor; mass


To view


A record


Now that you've got the suffixes and their meanings down, let's put them to good use. Here are some common medical terms that use the preceding suffixes, in context:

- Fibromyalgia is a common ailment in which one suffers chronic, widespread pain.

- The most common surgery performed in the United States is appendectomy, or the removal of the appendix.

Appendix appendectomy colon large intestine digestive ap vocab

- Bronchitis is the inflammation of the mucous membranes of the bronchi.

- To determine certain diseases, a biopsy may be performed, in which tissue is removed for analysis.

- A mammogram is the image(s) obtained by mammography, in which breast tissue is scanned for the possible presence of cancer.

Download the A&P Vocab: Suffixes eBook!

Want more suffixes and context examples? Download our free A&P Vocab: Suffixes eBook! You'll get 25 examples and stunning images from our best-selling Anatomy & Physiology app!


New Call\u002Dto\u002DAction


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Anatomy and Physiology: Measuring the Human Heart

When your heart pounds, do you think of how hard your ventricles are contracting to push blood in and out of the heart? Do you think of the astonishing pressure your veins and arteries withstand when you are out of breath and your adrenaline is pumping? Probably not. I know I certainly don't. If my body's flooded with adrenaline and my heart is pounding, I'm either exercising or being chased by a lion; in either case, my mind is going to be focused on not dying rather than how hard my heart is working.

But since we have a golden opportunity here, let's focus on the heart. Enough about hypothetical lions and even more hypothetical exercising.

If you have Anatomy & Function, go to Browse Common Topics and choose Cardiac Output. Follow along!

What is a heartbeat?

It goes far beyond “that sound in your chest.” Systole and diastole are the normal, rhythmic contractions of the ventricles as they pump blood in and out of the heart. The actual beating sound is usually described as lub DUB. The lub occurs when the mitral and tricuspid valves close and push blood out of the heart via the semilunar valves (systole), and the DUB occurs when the semilunar valves close and blood fills the ventricles (diastole).

Heart Valves Semilunar Mitral tricuspid aortic pulmonary

The average number of heart beats per minute is 72.


What is blood pressure?

As blood moves through your body, it puts pressure on the walls of your veins and arteries, much the way soda does when sucked through a straw. Blood pressure is the amount of force put on your blood vessels, caused by the flow generated by the heart as it pumps and any resistance that blood encounters as it moves through the vessels.

Artery Capillary Vein Blood Pressure

The heart beats faster during times of stress, exercise, or, in my case, when I see pictures of Richard Armitage, resulting in blood being pumped in and out of the heart and through the vessels at an increased rate. In this state, your blood pressure is high.

Blood Pressure Arteries Veins Blood Vessels

Blood pressure in a resting state is usually around 120 (systolic) over 70 (diastolic).


So, let's recap: Blood is pumped in and out of the heart and through the arteries and veins, the force exerted by the blood on the vessel walls is called blood pressure, and Richard Armitage makes my ticker go lub DUB, lub DUB, shalamalama ding dong.

Excellent. Moving on.


Measuring Cardiac Output

Now, the average amount of blood pumped per heartbeat is 70 mL. This is called stroke volume.

Cardiac output, on the other hand, is the volume of blood that each ventricle pumps out every minute. How much blood is that? Well, let's find out!

To find cardiac output, we'll first need to determine how many times your heart beats per minute. To do this, place your hand over your heart and count the beats for exactly one minute. Ready? Go.

Cardiac Output Heart Blood Volume

Okay, at the end of a minute, my heart beat 74 times. I will take that and multiply it by the stroke volume, which is 70 mL.

My cardiac output is 5180 mL/minute, or 5.18 L. How about you? What did you get? For fun, do 30 jumping jacks and then measure your cardiac output. How much of a difference do you see between your resting state result and your jumping jacks result?


Learn More

Want to learn more about the various ways to learn and understand human anatomy? Then check out Anatomy & Physiology by Visible Body. It will change the way you learn A&P forever!

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Learn Muscle Anatomy: Knee Joint Group

As I sit here, typing, I've got my legs crossed. My chiropractor would probably throw something at my head if he knew. Oh well. Is YOLO still a thing? Because YOLO.

Where my legs are crossed (at the knees) there are several muscles of the lower limbs in play. And of course there are—do you know how many anatomical structures it takes to move your knee? Probably more than you think. 

Want to follow along? I'm using the new Muscle Premium for iOS—we added bursae! (Hey, all you PC, Mac, and Android users, not to worry. Your bursae are coming soon.)

Knee joint bursae muscles patella

Muscles of the Knee Joint

The muscles of the knee joint are incredibly important. They move when you do—when you walk, run, dance, stretch your legs, or make any action you can think of that involves bending the knees.

There are two muscle groups that act on the knee joint: the quadriceps femoris and the posterior compartment of the proximal leg. In addition to these groups are the plantaris, articulus genu, semiteninosus, semimembranosus, and popliteus.

Knee joint muscle group quadriceps femoris resized 600

Let's take a look at the quadriceps femoris group.


Quadriceps Femoris Group




Rectus femoris

Originates on the anterior inferior iliac spine and a groove superior to the acetabulum; inserts on the common tendon of the quadriceps enclosing the patella, and on the tibial tuberosity

Extension of the leg at the knee joint; flexion of the hip

Vastus lateralis

Originates on the greater trochanter and upper lateral surface of the linea aspera; inserts on the patella via the quadriceps tendon, and the tibial tuberosity via the patellar ligament

Extension of the leg at the knee joint

Vastus intermedius

Originates on the upper two-thirds of the anterior and lateral surfaces of the femur; inserts on the common tendon of the quadriceps enclosing the patella, and on the tibial tuberosity

Extension of the leg at the knee joint

Vastus medialis

Originates on the intertrochanteric line and medial lip of the linea aspera; inserts on the common tendon of the quadriceps enclosing the patella, and on the tibial tuberosity

Extension of the leg at the knee joint



The body employs a bunch of different anatomical structures to keep friction down, and bursae are one of them.

Bursae bone muscle joint resized 600

Bursae are fluid-filled sacs that can be found anywhere skin rubs over bone, and where a muscle, ligament, or tendon glides directly over the periosteum (outer surface) of a bone. The synovial fluid in the bursae linings provides lubrication, enabling freedom of movement between contiguous connective tissue surfaces.

The bursae found in the knee include the superficial prepatellar, superficial and deep infrapatellar, medial and lateral gastrocnemius, suprapatellar, and quite a few more.


Knee Extension

So, I'm still sitting with one knee crossed over the other and somewhere my chiropractor just became enraged without knowing why. If I stand, however, I will be straightening, or extending, my knees.

Extension increases the angle between body parts. Flexion decreases the angle. Stand up for a moment and keep your legs perfectly straight—this is extension. The angle is around 180 degrees. Now, stand on one leg and lift the other until it's bent at the knee—this is flexion.

Knee flexion extension movement muscle action

And now I'm going to give my chiropractor's heart a rest and put both my feet on the floor.


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Year in Review: 7 Coolest Medical Stories of 2013

2013 was a pretty amazing time for the medical world. New technologies emerged, 3D printing became all the rage, a new ligament was “discovered,” the fountain of youth was discovered (not really, but keep reading), and plenty more! 

To cap off this year, we want to take a look at seven of 2013’s most interesting health and medical stories.


1. A robot assisted with a coronary stenting procedure for the first time.

Robotic assist coronary bypass stents

Why robots, you ask? Well, think of the control. I don’t know about you, but I can’t draw a straight line let alone stick a catheter in someone’s heart. The cardiology team at University of California at San Diego’s Sulpizio Cardiovascular Center, led by Dr. Ehtisham Mahmud, FACC, obviously felt the same way, and completed not one but two robotically assisted angioplasty and stenting procedures.

Let the SkyNet jokes commence.


2. 3D printing entire organs will be all the rage within the decade.

3D printing heart

While 3D printing has been around for about 30 years, a highly successful kick-starter campaign in 2012 made it available to the public for pretty much the first time, and ever since 3D printing has taken the world by storm.

In November, a team of bioengineers announced that within a decade they will be able to 3D print a human heart from not the relatively easy-to-come-by plastic that is used for commercial 3D printing, but from the recipients’ own cells.

Stuart K. Williams, executive and scientific director at Louisiana’s Cardiovascular Innovation Institute, had only this to say: “I said a full decade to provide some wiggle room.”

3. A man’s hand was grafted to his foot.

Blood arteries veins hand ankle surgically attached

I think that’s the greatest thing I’ve written all year.

Without a blood supply, organs, limbs, and muscles die. If you’ve ever stuck your hand into a snow blower to try and clear a blockage and ended up with a few less fingers than with what you started, you know that time is of the essence when it comes to reattaching limbs.

Normally, severed limbs are put on ice to slow down necrosis. To save a man’s hand that had been severed in an automobile accident, some fast-thinking doctors surgically attached its arteries to those in his ankle, which prevented the limb from dying and significantly increased the chance for it to regain normal function once it was reattached to his wrist. 

4. Artificial blood is finally going to become a thing.

Systemic circulation arteries veins artificial blood

How many times have you heard about the incredible demand for blood and thought, “Why aren’t scientists making blood?” If you haven’t thought this about blood, you’ve probably thought it about oil.

A team at Babes-Bolyai University in Romania have concocted an artificial blood recipe that has been having some very encouraging results. The artificial blood’s main ingredient is a protein called hemerythrin that is used for oxygen storage and transfer.

So far, the artificial blood (which really needs a cool name) has only been used in mice trials, but the results are pretty spectacular: no inflammation or rejection. The mice have “remained indifferent,” according to team leader Professor Radu Silaghi-Dumitrescu.

5. Talking to some patients in comas or vegetative states isn’t just a movie cliché.

Brain neuro coma vegetative listening

You’ve seen it in movies before: in a touching and vulnerable scene, the main character talks to a comatose character, who then wakes up two scenes later having heard him or her. As impossible as that may seem, it’s not too far from reality.

Scientists at the Medical Research Council Cognition and Brain Sciences Unit (MRC CBSU) and the University of Cambridge studied 21 patients in vegetative or minimally conscious states. The patients heard a series of words and were told to parse out a particular word; one patient was able to successfully filter out the erroneous words and focus on the prompted word, while others weren’t able to hone in on that word but focused on other novel words. Bottom line: some minimally conscious patients are paying attention.

“Not only did we find the patients had the ability to pay attention, we also found independent evidence of their ability to follow commands,” said Dr. Srivas Chennu at the University of Cambridge.

6. The fountain of youth is less of a fountain and more of a metabolic coenzyme.

Mitochondria aging process reversed NAD

In December, the beauty industry quaked in fear at the announcement that American and Australian scientists reversed the aging process with the application of a compound called NAD+ (nicotinamide adenine dinucleotide).

Applied to aging mice, NAD+ affects the aging process at the mitochondrial level. It had been the hope of the scientists to slow the process of aging, but they were shocked to discover that NAD+ didn’t slow it down—it reversed it. The mice, which had been experiencing a slew of age-related ailments, experienced an increase in muscle tone and energy.

Human trials of NAD+ are slated to begin in 2014.


7. The verdict is in: antibacterial soaps and sanitizers aren’t any better than regular soap.

Antibacterial soap sanitizer FDA

I actually didn’t find this one too shocking. All I had to do was watch my YiaYia wash her hands with her gross-smelling glycerin soap to know that one wasn’t any better than the other. She’s been using that stuff for years, while my mother’s been an advocate of antibacterial soap for a while, and neither of them have experienced anything better than the other. At least the dumb glycerin soap isn’t going to contribute to the creation of some giant, antibacterial-resistant superbug.

The FDA announced that antibacterial products, most of which claim to remove 99.9% of germs, need to put their money where their mouth is. As studies have shown that antibacterial products don’t reduce germs any better than regular soap, these companies need to supply evidence to the contrary or change their labels and claims to keep their products on the market.

Maybe we won’t perish at the metaphorical hands of a superbug after all!

Thanks for an amazing year! See you in 2014! 

3D Skeletal System: 5 Cool Facts about the Hip Bones

I know, I know, it's another blog post about the pelvic girdle. Well, sort of. Sometimes it's a thankless job, holding the weight of our upper half, so this post is going to be dedicated to my favorite pair of jutting wings—the hip bones!

So sit down and take a load off, and let's dive in!


1. The proper term for the hip bones is "os coxae."

Os coxae hipbones ilia ischium pubis pelvic girdle

"Os coxae" comes from the Latin words "os" meaning bone and "coxae" from the old Latin word for hip.


2. Each hip bone is actually made up of three bones.

It may look like one bone, but each hip bone is made up of the ilium, pubis, and ischium, which are completely fused.


3. There's a cavity in each hip bone.

Acetabulum hip socket hipbones os coxae

No, seriously! The concave cavity in the hip socket is known as the acetabulum, which is where the head of the femur articulates.


4. There are noticeable differences between the male and female hip bones.

The female hip bones are more delicate and shallow than the male's, with less sloped ilia. However, the superior aperture of the female pelvis is larger and more circular than the male's.

5. There is a giant hole between the hip bones.

Superior aperture pelvic girdle os coxae hipbones

Well, technically it's a space more than a hole. The superior aperture is the space that divides the abdominal cavity from the pelvic cavity. If you look at the pelvic area from a superior view, you will see the superior aperture is circular and formed by the hip bones, sacrum, and pubic symphysis.


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Five Cool Facts about the Middle and Inner Ear

Do you hear what I hear? It’s the sound of some awesome anatomy truthiness coming atcha! The middle and inner ear are kind of overlooked in the cool anatomical structures department, so I decided to honor some of the awesome things inside that head of yours.

1. The smallest bone in the body resides in the middle ear.

Stapes middle ear auditory ossicles inner ear cochlea

The stapes, also known as the stirrup, is one of the auditory ossicles, consisting of a head, neck, two crura, and base. It looks sort of like a wishbone, or, well, a stirrup! Sound waves strike the eardrum and the vibrations travel into the middle ear. When these vibrations reach the stapes, it pushes the membrane of the oval window, building pressure waves in the cochlea, and this begins a process that generates nerve impulses.


2. The smallest muscle in the body is also in the middle ear.

Stapedius muscle middle ear stapes inner ear cochlea

The stapedius muscle attaches to the stapes. It stabilizes the bone and dampens large vibrations to protect the oval window from loud noises.


3. The ear is not just for detecting sound.

vestibule semicircular canals ear inner ear bony labyrinth

The semicircular canals of the vestibule of the inner ear are responsible for balance. They provide sensory input for equilibrium by detecting acceleration or deceleration. Each canal ends in an ampulla; these ampullae contain fluid that moves when the head does. The movement of the fluid causes hair cells to bend, which generates nerve impulses.


4. The ear drum actually looks like a drum.

Tympanic membrane ear drum external auditory 

The ear drum is a thin, oval-shaped membrane that separates the external auditory canal from the middle ear. Sound waves strike the ear drum, creating vibrations that travel to the auditory ossicles.


5. You have a pressure equalizer in your head.

Eustachian tube auditory canal inner ear

Do your ears sometimes “pop” when you yawn? This is actually the Eustachian tube opening, stabilizing pressure in the middle ear with outside air pressure. The Eustachian tube is a channel that links the cavity of the middle ear with the nasopharynx

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