The Pectoral Girdle 1: A Few Bones

We are going to start in the region one can loosely think of as the shoulder and upper chest.  A combination of bones and muscles here make up what is called the pectoral girdle.  A girdle was similar to a belt that was worn chiefly by women of the middle ages to help support their mid-sections and help make them look slender.  Similarly, the pectoral girdle attaches the upper extremity to the body and helps support it in its varied movements.  Pectoral is derived from Latin pectus, meaning breast or chest.  As one might infer from the name the pectoral girdle encompasses the upper chest.

Lets dive right in, first we are going to look at the bone structure.

Focus on the scapula.  The scapula sits posterior to, or behind, the ribs.  In Latin the ribs are called costae; almost all the anatomical names relating to the ribs involve cost-, for example the joint between the ribs and the clavicle bone is called the costoclavicular joint, which makes sense because the name tells you what it joins.  But I digress, back to the scapula...think of the scapula as the major base of the shoulder and all the movements going on up there.  It is the chief attachment of the upper extremity with the body, joining the humerus, the big upper arm bone, with the clavicle, which in turn connects to the sternum, as mentioned above.  It sits against the rib cage and slide all over, forward and back, up and down, allowing the shoulder to move freely.  Now it starts to get hard as we move into all the many parts of the bone to learn, the muscles, the borders, and all the attachments locations and movements.

Lets examine just the scapula...

This picture shows an anterior view of the left scapula.  The scapula is a triangular shaped bone that is very mobile.  If a person was attached we would be face to face with them and this picture would be on our right, but since we always name left and right from the patients prospective, it is the left scapula.  The superior border is toward the head, note the two bumps of bone sticking out of the top left (most superior lateral aspect), the lateral border is what you can feel if you grab under your arm pit, the inferior angle points toward the toes, and the medial border sits near, and posterior to, the spine.  Borders are an extremely important concept in anatomy as many of the muscles which you will later learn attach at these points.  To continue our orientation and bone landmarks, look at the area labeled subscapular fossa.  Sub means beneath in Latin and will be a common prefix and fossa is Latin for a hollow depression or pit and will also be a common term.  This is a concave area, shaped like a cupped hand, if it was flat on a table and we poured water into it, it would fill like a bowl.  Similarly in the body the subscapular fossa is filled by a large muscle, called the subscapularis (makes sense right?).  Muscles will be individually covered later but if you can start to establish connections it will help.

The glenoid fossa, glene is Greek for socket, is where the head of the humerus bone, upper arm bone, attaches to, or articulates as we say in anatomy, with the shoulder. To continue integrating our anatomy terms, one could say that the proximal end of the humerus articulates with the glenoid fossa.  It functions as a ball and socket joint which makes sense, if it was a hinge one couldn't rotate the shoulder all the way around with such freedom of movement (think of swimming or throwing a baseball).

Next look at the two bumps we mentioned earlier, the coracoid process and the acromion process.  Coracoid in Greek essentially means like a beak, because it is shaped like a a bird's beak.  Acro is from the Greek akron which means top most, or highest, and is named as such because it represents the most superior and lateral point of the shoulder.  The coracoid process projects somewhat lateral and anterior and serves as an attachment site for many muscles, which we will get to, and with the acromion process, functions to stabilize the shoulder joint.  The acromion process also has a bunch of muscles associated with it and it is where the scapula directly articulates with the clavicle bone.  Because most things in anatomy are named for what they do or connect, the joint is aptly called the acromioclavicular joint.  The last thing to note on the anterior portion is the little notch along the superior border, called the suprascapular notch, supra being Latin for above.  (It is also called the scapular notch as noted above, but I would use supra, the more detailed descriptions are generally better.)

In order to show what these bones look like with all the ligaments filled in look at this (and don't worry what they are or where they are going for now)...

Understand that many connections exist, but if we break them down and attack it piece by piece, it really is a logical puzzle that becomes manageable.  Note the things I describe already and try to correlate them with this picture, ie how the acromion connects with the clavicle. 

Now for the posterior scapula...

We are now looking at the back, or posterior, view of the right scapula.  To orient ourselves, note the medial border, think of the spine sitting near it, and the lateral border being the side of the body.  The coracoid and acromion processes sit superiorly.  Note the large ridge of bone going across, the spine of the scapula, it is like a large wall that divides the posterior part into two regions, a superior region above called the supraspinous fossa (depression above the spine), and an inferior region below called the infraspinous fossa (depression below the spine).  An important muscle sits in each fossa, the supraspinatous sits in the supraspinous fossa (nice for them to name it the same thing huh?) and the infraspinatous muscle lies in the infraspinous fossa (more on these later).  The acromion process is the just the continuation and tip of the spine, projecting laterally and somewhat anteriorly to lie over the glenoid fossa.  Remember that the anterior view is concave so the posterior view is some what convex (like an upside-down bowl).

On to the next one; the clavicle bone.

The clavicle is an S shaped bone that is quite small and fragile.  It is easily palpable is most people, meaning you can feel it on the skin, and can be seen as a bulge on some.  It connects the sternum (essentially the ribcage) and the scapula.  Clavicula in Latin means little key, because during a certain motion with the shoulder called abduction, it turns like a key.  Medially it articulates with the manubrium of the sternum, labeled sternal end above, (don't worry about what the manubrium is yet) at the sternoclavicular joint (once again the name makes sense).  The sternoclavicular joint is unique, the clavicle wants to try to move anteriorly and posteriorly, so the body must restrict that movement.  As such the sternoclavicular joint is characterized by thick ligments, anteriorly and posteriorly, to prevent that movement. These ligaments are very strong and it is far more common for the bone itself to fracture before dislocating from these ligaments. (For more on the sternoclavicular joint see the next post).

Laterally it articulates with the acromion process, as mentioned above, and the joint is named the acromioclavicular joint.  It also has other attachments and ligaments which we will cover shortly, just think of these as the big ones for now.  The purpose of the clavicle is to allow the scapula, and thus the arm, to move freely and be connected to the thorax without limiting its range of motion.  But as a result of its placement, force experience in the arm, say by falling and landing on a hand, is transmitted along the arm, through the scapula, and into the clavicle to the thorax.  With the clavicle being the weakest bone is this chain, is it commonly fractured. (Note: the scapula is very hard to break and usually only does with severe trauma.)

See the fractured clavicle?  It commonly breaks about two thirds of the way down, proximal to distal.   The proximal end usually goes up while the lateral/distal side usually tilts down because the weight of the arm is weighing it down.  In order for it to properly heal it is necessary to immobilize the arm in a sling for a number of weeks, taking the weight off and allowing it to heal.

Can you now see why we call it the pectoral, or shoulder, girdle?  The scapula and clavicle act to stabilize and support the arm and upper chest.

Now that we have a foundation of the bones, next we will discuss the many ligaments holding them together.

Planes, Relationships, and Some Basic Terms

We will start with some basic anatomical planes.  First, take a look at the picture below (hyper-linked to the site I got it from #copyrights)

Note the three major planes.  If you imagine a magic trick and someone getting sawed in half, that is the transverse plan.  Trans is a Latin prefix that means something is moving across or through, examples: transaction, money is being moved across or exchanged, transduction, energy is being moved, and transfer.  Getting comfortable with Latin roots will help, I will try to include them as often as possible, because I guarantee they will be reoccurring themes.  The transverse plane is also called the horizontal plane.  Planes are often used in medical imagining and in histology, the branch of biology dealing with the study of tissues, as often you will hear things referred to as 'cut in a transverse plane' or 'this slide was prepared from a transverse section'.

The second plane, the coronal plane, is what happens if somebody gets caught in a high speed automatic door.  It is also often called the frontal plane.  The third plane is called the sagittal plane and cuts the body in a plane between the eyes. It is often called the median plane, median referring to the middle. This is the only plane that has symmetry, the others do not.

Now take a look at the next image, we are going to add relations to our planes;

We will again start with the transverse, or horizontal, plane.  As we travel up toward the head from the stomach and waist area, we are traveling superiorly.  If we travel toward the feet we are traveling inferiorly.  Think of related words, if something is superior it is above the object that or person that is inferior.  'Dave is a superior baseball player to Andrew, who is clearly inferior,' as an example.  Similarly we describe anatomical things in relation to each other, the feet are inferior to the knees, the head is superior to the thorax, etc.

In the saggital plane, or median plane, we use the terms medial and lateral.  Medial means located closed to the middle while lateral means further away.  For example, if you are comparing your ear to your finger tips, you could say that your fingers are lateral to your ear, (side note: anatomical position is what we refer to as someone as pictured above, arms slightly out, palms forward.  It is the standard anatomical reference), or that your ear is medial to your fingers.  Be careful, these are comparative terms so they only mean something in relation to something else.  They are commonly used to name muscles, nerves, or other things in the body that are similar in function or location; for example in the general region of your shoulder is a tangle of nerves called the Brachial Plexus (you will come to know and love/hate this structure).  At a specific subdivision it splits into a medial cord, a lateral cord and a few others.  For the most part anatomists named the body as they saw it, so as you can probably figure out the medial cord of the Brachial Plexus sits closer to the middle of the body and the lateral further away.  This will all make more sense as we progress.

Lastly let us discuss the coronal plane, or frontal plane.  For this plane we associate the terms anterior, from the latin ante- which describes something as in front of something else (think how an ante in a poker game is collected before the round begins, or antebellum referring to before the US Civil War), and posterior, from the latin post- denoting something as behind or after (think postoperative care is what you must do after a surgery to heal, postmortem refers to after death).    If I am standing in front of a wall and press the tip of my nose into the wall, that is the anterior part of my body.  If I turn around and touch my butt to the wall, the posterior aspect of my body is touching the wall.  That's also why posterior is a slang term for the butt, though outdated.  These concepts are similarly comparative, the forehead is anterior to the back of the head and the spine is posterior to the heart.  Again, many anatomical structures are named with these terms, for example in dentistry we pay very close attention to the anterior superior alveolar nerve and the posterior superior alveolar nerve.  Both provide sensory information from the maxillary teeth (the ones on top), with, as you guessed, the ASAN doing the teeth in front of the PSAN.

Other terms: Commonly used are also proximal and distal.  Commonly associated with the extremities, the arms and legs, proximal means closer to the body while distal means away from.  For example, the fingers are distal to the shoulder, or the shoulder is proximal to the hand.  Dorsal means the same thing as posterior and ventral means the same thing as anterior.  Dors- in Latin means pertaining to the back, think of a fish having a dorsal fin, while ventral comes from the Latin ventr- meaning pertaining to the stomach.   Rostral and Caudal are opposing terms that are more antiquated and used less frequently.  Rostral is synonymous with superior and caudal is the same as inferior, i.e., the feet are caudal to the knees, the head is rostral to the heart.

Superficial and Deep are terms associated with a relation to the skin.  For example look at your hand and arm.  You will probably see veins, but not pulsing red arteries.  That is because veins lie superficial to arteries (generally).  Evolutionarily that makes sense, if a vein gets cut, you might bleed some but will probably be okay, but if your aorta off the heart was right under the skin of your chest and you got a small cut, you might have serious problems.

Try to get comfortable using these terms and thinking spatially in these terms.  I find that imaging some of the pictures above and rotating them in my mind when I am trying to figure out a test question is very helpful, it might work for you too.  These are just the basics and there are more terms that are associated with specific areas, radial and ulnar in the forearm for example, which I will deal with in more detail when we get there.

Lastly, bookmark this page of Latin terms, it pays big time to just browse it or connect the dots when learning new things.

http://en.wikipedia.org/wiki/List_of_medical_roots,_suffixes_and_prefixes

Overview of the Site and Objectives

To my newest readers,
In my experience, anatomy is a subject best learned in a class room setting. There are simply no substitutions for highly qualified lectures and a cadaver (human body) dissection where one can ask questions and try to assemble the large volume of facts into conceptual and applicable knowledge.  That having been said, I am going to try and create a site where the starting graduate student, knowing nothing about anatomy going in, like I did, or anyone interested in the subject, can come for supplemental information to aid in the process of understanding the wonderful and mysterious human body.
I am not a qualified anatomy professor.  I have not authored textbooks.  But I do have a detailed knowledge, a love of teaching and explaining things, and enough computer know how to try to put it together.  I will be borrowing from various other sites and works and will do my best to cite them as I go and provide external links to sites that helped me study.
A note about learning styles: Everyone learns differently. In the American education system, especially in the science classes, it tends to be a reductionist approach.  In high school I learned that A-->B-->C, for example DNA-->RNA-->Protein.  In college we delved deeper and looked at the pathway from A-->B and said, well what really in happening is A-->Ax-->Ay-->Az-->B, in this case examining the multitude of transcription factors and various proteins that come together and bind the DNA in certain ways in order to initiate transcription into RNA.  I, personally, love the reductionist approach and find it conducive to my logical, step oriented brain.  I would encourage you to think about how you like to learn and what ways work the best for you; examining pictures and contemplating spacial relations? reading text and building relationships between words?  If you can understand what is best for you it will help you tremendously in the long run because in anatomy you must synthesize huge volumes of information and understand it well.  To that I end I will try to incorporate as many styles as possible to try to give the best learning experience to everyone.  Many times it is helpful to look at something a different way, I certainly find that to be the case.
Lastly, please post any questions and I will answer them, and if I cannot answer it satisfactory, I will take it up with my anatomy professors and get you an answer.

Under Construction

Content to follow this summer