The Brachial Plexus

The brachial plexus is an important group of nerve fibers running from the spinal cord to the arm, providing sensory and muscle innervation.  It is an alternating union and branching of nerves to reorganize the terminal branches of multiple spinal levels. Understanding it is a first, and critical step, in anatomy.  (Don't bother with mnemonics here, you need to know it cold)

First, an overview.  Think of it like this.

Ignore the names for now.  The brachial plexus is the collection of nerves made up of C5, C6, C7, C8, and T1, but only the ventral rami.  These 5 rami mix and twist in a weird way that you will, probably since you are reading this, have to memorize.  It looks weird at first but after you practice drawing it (both sides!) you will get it.

 The 5 Rami become 3 Trunks, the 3 Trunks become 6 Divisions, the 6 Divisions become 3 Cords, the 3 Cords become 6 Branches.  The 5 Rami are C5, C6, C7, C8, and T1.  The 3 Trunks are Upper, Middle and Lower, going superiority to inferiority, e.g. C5 and C6 merge to form the Upper Trunk.  The 6 Divisions are not named (note: in the body 3 are more anterior and 3 are more posterior). The 3 Cords are really important for naming, as labeled above, the Posterior, Lateral, and Medial Cords, so named again due to their location relative to the axillary artery.

Branches (memorize all of this, if you are not familiar with the muscles, google it or wait for an upcoming post)

Off the Rami:
 1. Long Thoracic Nerve (C5,C6,C7)- Innervates the Serratus Anterior
 2. Dorsal Scapular Nerve (C5)- Innervates the Rhomboid Major, Rhomboid Minor, and Levator Scapulae  (all back muscles)

Off the Upper Trunk:
 1. Suprascapular Nerve (C5,C6)- Innervates the Supraspinatus and Infraspinatus (back muscles)
 2. Subclavius Nerve (C5, C6)- Subclavius (essentially a useless muscle)

Off the Lateral Cord:
 1. Lateral Pectoral Nerve (C5,C6,C7)- Innervates Pectoralis Major (clavicular portion)
 2. Musculocutaneous Nerve (C5,C6,C7)- Innervates Biceps, Coracobrachialis, Brachialis and does sensory (like  all nerves that ends in -cutaneous)
 3. Lateral head of Median (C5,C6,C7)

Off the Medial Cord:
 1. Medial Pectoral Nerve (C8, T1)- Innervates Pectoralis Minor and Pectoralis Major (sternocostal)
 2. Medial head of Median (C8, T1)
 3. Ulnar Nerve (C8, T1)- Innervates stuff in the arm, also is the 'funny bone' you hit when you strike your elbow.
 4. Medial Brachial Cutaneous Nerve (C8, T1)- Sensory in arm
 5. Medial Antebrachial Cutaneous Nerve (C8, T1)- sensory in arm

Off the Posterior Cord:
 1. Radial Nerve (C5,C6,C7,C8,T1) - Lots of stuff in the arm
 2. Axillary Nerve (C5,C6)- Innervates the Deltoid and the Teres Minor muscles
 3. Thoracodorsal (C6,C7,C8)- Innervates the Latissimus Dorsi muscle.
 4. Upper Subscapular (C5,C6)- Innervates the upper part of the subscapularis
5. Lower Subscapularis (C5,C6)- take a guess... lower part of the subscapularis.

Practice drawing it, youtube has some good videos (https://www.youtube.com/watch?v=gTas7ijp0YE). Remember to practice both sides!!! 

More information- locations and arterial relations. Rami and Trunks are found in the Posterior Triangle of the Neck and are associated with the Subclavian Artery.  Divisions are found behind the clavicle and are associated with the Subclavian and the 1st Part of the Axillary Artery.  Cords are in the Axilla and associated with the 2nd part of the Axillary Artery.  Branches are in the Axilla and associated with the 3rd part of the Axillary Artery. 

###The Key Landmark in all this is the large capital M formed by the medial cord, lateral cord, and terminal branches.  On a practical you should always find the M, orient yourself, and trace back/fore wards from there.

Brachial Plexopathy: What can go wrong?  You can have inflammation or an immune reaction, neoplasms and cancer growths, tears due to wounds, constriction by scar tissue, to name a few.  Great test questions ask about someone stabbed in a certain place, or a certain group of muscles in not functioning, and you must reason out which nerve is the problem, to do that you must know it cold.
A few major pathology itemes:
-Erb's Palsy (Erb-Duschenne-Palsy) is the name when C5 and C6 are severed, most common during a difficult childbirth or someone falling awkwardly on their head/shoulder. "The signs of Erb's Palsy include loss of sensation in the arm and paralysis and atrophy of the deltoid, biceps, and brachialis muscles. The position of the limb, under such conditions, is characteristic: the arm hangs by the side and is rotated medially; the forearm is extended and pronated. The arm cannot be raised from the side; all power of flexion of the elbow is lost, as is also supination of the forearm. The resulting biceps damage is the main cause of this classic physical position commonly called "waiter's tip.""
-Klumpke Paralysis: A lower injury, generally C8 and T1, "The subsequent paralysis affects, principally, the intrinsic muscles of the hand and the flexors of the wrist and fingers The classic presentation of Klumpke's palsy is the “claw hand” where the forearm is supinated and the wrist and fingers are flexed."


Practice Test Questions, mix of my own and UofMichigan Medical School
-Answers below-

1. During a fight a man is stabbed in the lateral chest beneath the right arm. The wound does not enter the chest cavity. Physical examination reveals that the vertebral (medial) border of the patient's scapula projects posteriorly and is closer to the midline on the injured side. On return visit the patient complains that he cannot reach as far forward (such as to reach for a door knob) as he could before the injury. The nerve injured which caused these symptoms is the:
1. axillary
2. long thoracic
3. musculocutaneous
4. radial
5. suprascapular

2. Name the 3 muscles innervated by Dorsal Scapular

3. Given their respective locations, what two nerves can be damaged during excision of axillary lymph nodes?

4. A person sustains a left brachial plexus injury in an auto accident. After initial recovery the following is observed: 1) the diaphragm functions normally, 2) there is no winging of the scapula, 3) abduction cannot be initiated, but if the arm is helped through the first 45 degrees of abduction, the patient can fully abduct the arm. From this amount of information and your knowledge of the formation of the brachial plexus where would you expect the injury to be:
 1. axillary nerve
 2. posterior cord
 3. roots of plexus
 4. superior trunk
 5. suprascapular nerve

5. You suspect a patient of yours has a soft tissue hematoma.  He presents with winged scapulae, he has trouble fully abducting, and both scapulae are noticeably protrusive.  Where could you reasonably localize the problem to and why?

6. The cords of the brachial plexus are:
 1. above the clavicle, medial to the scalenus anticus (anterior scalene).
 2. above the clavicle, behind the scalenus anticus (anterior scalene).
 3. at or below the clavicle, closely related to the axillary artery.
 4. at or below the clavicle, closely related to the axillary vein.

7. In a diving accident that severed the spinal cord below the sixth cervical vertebra, which muscle would be affected?
  1.Deltoid
  2. Infraspinatus
  3. Latissimus dorsi
  4. Levator scapulae
  5. Trapezius

8. During a strenuous game of tennis a 55 year old woman complained of severe shoulder pain that forced her to quit the game. During physical examination it was found that she could not initiate abduction of her arm, but if her arm was elevated to 45 degrees from the vertical (at her side) position, she had no trouble fully abducting it. Injury to which muscle was responsible?
  1. deltoid
  2. infraspinatus
  3. supraspinatus
  4. teres major
  5. trapezius



Answers (with explanations)
1. Long thoracic
Remember--an injury to the long thoracic nerve denervates serratus anterior, meaning that there will be no muscle protracting the scapula and counteracting trapezius and the rhomboids, powerful retractors of the scapula. The long thoracic nerve is derived from the nerve roots of C5-7; this nerve is particularly vulnerable to iatrogenic injury during surgical procedures because it is located on the superficial side of serratus anterior.
The axillary nerve innervates teres minor and deltoid. It wraps around the surgical neck of the humerus and is endangered by fractures of the surgical neck. If the axillary nerve was damaged and deltoid was denervated, the patient would be unable to abduct his upper limb beyond 15 to 20 degrees. The musculocutaneous nerve innervates biceps brachi, coracobrachialis, and brachialis. If this nerve was disrupted, the patient would be unable to flex her or his forearm, and have weakened arm flexion. The radial nerve innervates extensors of the forearm and triceps brachi--if this nerve was injured, the patient would no longer be able to extend forearm, but only have slightly weakened arm extension (latissimus is the powerful extensor of the arm). Finally, the suprascapular nerve innervates supraspinatus--the muscle that initiates abduction. Damage to this nerve would prevent the patient from starting to abduct her or his arm.

2. Rhomboid Major, Rhomboid Minor, and Levator Scapulae


3. Thoracodorsal and Long Thoracic

4. Suprascapular nerve
Let's take the observations one by one to break down this question. If the diaphragm is functioning normally, you know that the phrenic nerve is probably uninjured, which means that the C5 root has not been damaged. Since the scapula is not winged, there was no damage to the long thoracic nerve or the C5-7 nerve roots. Finally, since the patient cannot initiate abduction of the arm, you know that the suprascapular nerve is injured and supraspinatus has been denervated. But, the patient can abduct the arm once it is lifted to 45 degrees, so the deltoid muscle and the axillary nerve must be intact.
Taking the answer choices one by one: The axillary nerve is ok, because deltoid is functioning. The posterior cord of the brachial plexus must also be intact, since this cord gives off the axillary nerve. The roots of the brachial plexus are ok, since the phrenic nerve and long thoracic nerve (which are derived from the roots) are still functioning. The superior trunk of the brachial plexus must also be undamaged, since this trunk contributes to the posterior cord which is intact. So, this means that the injury must be to the suprascapular nerve.

5. The area of C5-C7, his long thoracic nerve is affected, classically presenting with a weakened winged scapulae.

6. at or below the clavicle, closely related to the axillary artery
The cords of the brachial plexus are closely related to the axillary artery, at or below the level of the clavicle. You should have seen this in the dissection--the cords were wrapped around the axillary artery. The axillary vein is anterior to the axillary artery and is not associated with the cords of the brachial plexus. As far as the scalene muscles go, you'll learn more about this in the head and neck, but know that the roots, not the cords, of the brachial plexus are the structures found between the anterior and middle scalene muscles.

7. latissimus dorsi
If the spinal cord was severed beneath the 6th cervical vertebra, all nerve roots below C6 would be affected. So, latissimus dorsi, which is innervated by the thoracodorsal nerve (C6, C7, C8) would be affected. Deltoid is suplied by the axillary nerve (C5, C6). Infraspinatus is supplied by the suprascapular nerve (C5, C6). Levator scapulae is supplied by the dorsal scapular nerve (C5). Trapezius is supplied by the accessory nerve (CN XI). All of these nerves would be intact, so these muscles would not be affected after the accident.

8. supraspinatus
Supraspinatus is responsible for initiating abduction of the arm, while deltoid is responsible for continuing abduction of the arm past the first 15 or 20 degrees. Since this patient can abduct her arm when it is lifted to 45 degrees, deltoid seems to be intact. But, she can't initiate the motion, so you know that she has probably injured supraspinatus. Infraspinatus rotates the arm laterally, and teres major rotates the arm medially. Trapezius elevates and depresses the scapula--a problem with this muscle is most evident if a patient has trouble raising the acromion of her shoulder.

Neuroanatomy Introduction

This post will be an neuroanatomy and nervous system introduction because it is necessary to understand some basic aspects about the nervous system before trying to understand nerves in the context of anatomy. I will also assume a basic level of understanding about nerves and conduction here, so please post questions if I skip anything.


Some Basics
- A perikaryon is a term for the cell body of a neuron.
-The nervous system is generally broken into two parts, the Central Nervous System (CNS) which is essentially the brain and spinal cord, and the Peripheral Nervous System (PNS), everything else.
-A ganglion is a collection of cell bodies in the PNS.
-A nucleus is a collection of cell bodies in the CNS. BE CAREFUL it is easy to confuse this with a regular cell nucleus. Same word, it just means a different thing in neuro.
-A neuron is the structural and functional unit of the nervous system.  It exhibits two chief properties which we will over simply to keep it brief, irritability and conductivity.
-Nerves travel out of the CNS and into the PNS and go all over the body.  Most nerves traveling to the skin have the word cutaneous in their name (cutis means skin in Latin).

A basic neuron

The CNS (leaving out the brain for now so mostly just,) The Spinal Cord

As I mentioned last post, the spine is made up of individual bones called vertebrae. There are 7 cervical vertebrae, appropriately named C1 through C7, 12 thoracic, 5 lumbar, 5 sacral, and the coccyx, a fused mass of bone.

-Remember the vocab rostral and caudal because they are especially common in neuro.  Rostral means the same superior, or closer to the top of the head, while caudal means the same thing and inferior.

- The C1 nerve actually exits above the C1 vertebrae.  This is very important because there is a C8 nerve BUT NO VERTEBRAE.  The C8 nerve exits just caudal to the C7 vertebrae.  So above C7 all the nerves exit the spinal cord and enter the body ABOVE their vertebrae, and below C7 all the nerves exit and leave BELOW their vertebrae.  Or, another way, Cs above, and Ts and Ls below.

-The spinal cord begins at the medulla (in the brain) and continues until it terminates at the vertebrae levels of L1-L2.  Beyond that, nerves hang down and still exit, but the 'middle' is simply a space filled with cerebrospinal fluid.  Clinical correlation:  Ever heard of a lumbar puncture?  Ever watched the show House or any other doctor show?  To get a sample of the cerebrospinal fluid the most common method is the lumbar puncture, because with no spinal cord the chance of injury is minimal.

-There are 31 pairs of spinal nerves. C-8  T-12 L-5 S-5 C-1

-Nerves C5 C6 C7 C8 and T1 make up what is called the Brachial Plexus (more later).

A single vertebral body looks like this.  The in depth anatomy of the spine I will cover at a later point.

The Peripheral Nervous System
The PNS is everything outside the CNS, so everything except the brain and spinal cord.  It is composed of 12 pairs of Cranial nerves and 31 pairs of spinal nerves.  The cranial nerves are,

Each one has a series of functions, associated sympathetic and parasympathetics, certain pathways and relations, and is the topic of a head and neck anatomy course (maybe I'll get there eventually).

Of more immediate concern are the spinal nerves;
1. They are formed by:
         a. Dorsal Root (Sensory)
         b. Ventral Rool (Motor)
2. Divide Into:
          a. Dorsal Root (Mixed)
          b. Ventral Root (Mixed)
What does this mean?  Let me explain,

Lets say, for example, this is cervical vertebrae 5, C5.  The dorsal root is where all the sensory information it receives, in this case some skin on the arm, enters the central nervous system and is then passed up to the brain.  In contrast the ventral root is where all the motor signals sent down from the brain pass through, for example helping to contract the serratus anterior muscle.  So, think of the dorsal root as inbound traffic and the ventral root as outbound traffic.  Simple.  By the way if you didn't pick up on it, dorsal and ventral are named due to their location, I think of it as a dorsal fin on a fish, the fin being on the dorsal side, and the ventral side being a humans chest.

Looking a little further away, these two pathways mix.  They are simply called the dorsal and ventral ramus, or rami for plural (ramus means branch in Latin).  Each of them contains both sensory and motor fibers, so they are called mixed nerves.  Simple.  Got it. 

Dermatomes
A dermatome is the area of skin supplied by a single nerve.  There are very specific delineations in this pattern,

This pattern can, for example, help a doctor figure out which exact nerve is dysfunctional if a patient cannot feel anything in the specific area. I don't feel like listing out exactly what they all do so hit of Wikipedia of you need to memorize it.

3. More Pectoral Bones and Muscles/Nerves/Arteries/Veins

Starting with the Sternum
The sternum is the big bone on the front of your chest. Taking it from the top...

Put your hand on your throat.  Now move it down to the top of your chest.  You should feel a little dip of bone, like a cup.  This is called the suprasternal notch or the jugular notch.  It is the top part of the sternum bone. Because of the many important structures running near or behind it, it is a common target in martial arts, for example in jujitsu.  Check out this fight scene from the first Matrix movie, at 1:27 the agent throws a suprasternal finger strike.  Anyway, the manubrium (Latin for 'handle') is the large part beneath it and then it connects to the body of the sternum at the sternal angle.  The sternal angle is a cartilaginous joint with little movement  The manubirum articulates with the clavicles and the first two ribs.  All these are important landmarks because as you learn more about the heart, the various nerves, and other internal organs, you will constantly be seeing references to these, so it is helpful to learn them well now instead of having to keep looking them up later.

A common question on anatomy tests are what I call ice pick questions and they generally go: if you were to stab someone with an icepick at a certain place, what would you hit and in what order?  It requires the student to put together concepts, information, and 3D relationships.  A similar set of questions ask how specific structures are innervated and where those nerves come out of the spinal column, each vertebrae has a letter and a number (Brief Aside: There are 7 cervical vertebrae, called C1-C7, 12 thoracic, T1-T12, 5 lumbar, L1-L5, 5 sacral, S1-S5, and the coccyx, a mass of 5 fused vertebrae).  For example the nerve that innervates the muscle called Serratus Anterior is called the Long Thoracic Nerve, and it is a combination of nerves fibers from C5, C6, and C7, I will always list these after the muscle name.

Great Test Items to Know:

If you ice pick someone at the jugular notch, it will come out the back at T2.
The Manubrium goes from T2 to T4.
The Sternal Angle is at T4 and is about 140 degrees.

Now I am going to cover muscles for the first time.  Generally the format I will use is as follows
Muscle:  Name of the muscle
About: information
Actions: What is does
Origins: where the muscle fibers originate
Insertions: where the muscle fibers insert
Nerve Supply:  Which nerves control the muscle

Origin/Insertion:  A good way to think of this is where a muscle starts and ends.  But which is which?  A good rule to remember is a muscle will generally insert into whatever it is moving. Keep this in mind.

Blood supply will be covered separately because unlike nerves, there is no 1:1 connection, rather networks of blood vessels supply general areas, and even then arteries, but veins especially, tend to highly anomalous, that is, outside of the major vessels many of the smaller ones simply do as they please and travel where they want.  Lets do it...

Muscle: Pectoralis Major
About: The pectoralis major, commonly called the pec major, is the large muscle on the chest of males, and underneath the breast in females.  It is one of the main muscles used when bench pressing or doing push ups.
Actions:
1. Adduction of the Brachium (aDDuction is moving closer to the body, imagine flapping your arms like you are trying to fly, when your arm is moving downward, it is adducting.  The opposite is aBduction, part where your arms are moving up. And the Brachium is upper arm)
2. Medial Rotation of the Brachium (medial rotation is twisting in toward the body, hold your arm out and give a thumbs down, that is your arm in medial rotation, the opposite way, twist out, is lateral rotation)
3. Flexion of the Brachium (bringing the arm up and forward, benching press is flexion of the arm, or a bowling motion, or how a softball pitcher throws)
Origins: (see photo below as you go through them)
   1.Clavicular- The medial half of the clavicle
   2.Sternocostal- Anterior surface of the sternum and upper 6 costal cartilages, and abdominal portion of the aponeurotic tendon of the external oblique (an aponeurosis is generally where a muscles blends into a tendon, they are white, shiny, have paper like layers and there are a few important ones throughout the body.  Right now just memorize the information, I will go into more depth later)
Insertions: Lateral lip of the intertubercular groove of the humerus (front of the arm)
Nerve Supply:
1. Medial Pectoral Nerve (generally the sternocostal portion, or lower chest) (C8, T1)
2. Lateral Pectoral Nerve (generally the Clavicular portion, or upper chest) (C5, C6, C7)
As explained above, the letter/number referes to where in the spinal cord these nerves originate.  I will later go through all these nerves as an entity, it is called the Brachial Plexus, and in any anatomy class you will need to memorize it completely.  Why is it important?  Say you have a patient with upper shoulder/spinal trauma, if you can figure out which muscle actions do not work, you can figure out which part of the spinal cord might be affected (great test questions).

Now lets think through the origins and insertions (O/Is) and see if we can make sense of how they dictate the actions.  Muscle fibers only contract, they do not do complicated movements.  So if we imagine contraction, it makes sense the the arm will move closer to the body, up, and forward.  Boom, that's the 3 actions.  I prefer understanding the actions, as opposed to simply memorizing them all, because then you don't have to.  If you know O/Is you can figure out actions.

And where there is a major there is usually a minor.  If a structure has a name with major or minor, anterior or posterior, or superior/inferior, it is a good bet that the other also exists.

Muscle: Pectoralis Minor
About: Pec minor is the small little brother of pec major.  It sits behind, or posterior, to the pec major.  It is smaller and plays less of role in movement and big actions and more of stabilizer role for the scapula.  It helps connect the thoracic cage with the scapula.
Actions: Protracts (brings forward, opposite is Retract) the Scapula, and Stabilizes the Scapula
Origin: Ribs 3-5 (though often 2-4)
Insertion: Coracoid process of the Scapula
Nerve Supply: Medial Pectoral, (C8, T1)

Feeling overwhelmed yet?  Don't worry the more time you spend with this material the easier it gets, even though it seems impossible at first. 2 more muscles to go...


Muscle: Serratus Anterior
About: Also called 'The Pull Up Muscle',  The SA is a big muscle going from the ribs to the scapula.  When strongly defined the SA is the main muscle that produce the V shaped torso and is a main muscle used when throwing a punch.
Actions: Connects the ribs to the scapula, thus when it fully contracts it pulls the scapula forward, called protraction of the scapula.  But it is a big muscle and can contract in parts.  The bottom and top halves can contract separately causing the scapula to rotate too, though this is not a major function and thus not commonly listed (for examination purposes). It also helps stabilize the scapula.
Origin: Ribs 1-8
Insertion: Medial border of the Scapula
Nerve Supply: Long Thoracic Nerve (C5, C6, C7)
BIG NOTE and clinical correlation: Winged Scapula.  If the scapula is protruding from the back, giving it a winged appearance, it is commonly the result of a weak serratus anterior muscle or nerve problem.  If someone is really weak, cannot do one push up, and tries, you might see the scapula wing out from simple SA weakness.  Common test question:  A patient comes in from car accident and has sustained lacerations under his arm pit.  You notice his scapulae protruding on the right with a winged appearance.  What nerve has been severed?

Note the winged scapulae

Muscle: Subclavius
About: This is the first of some muscles that I will be blogging about that are simply not very useful. It goes from the ribs to the clavicle.  It is always funny to make fun of someone and call them useless using anatomy. 
      Karen: "Jon why do you never help with are lab group dissections. Stop messing around."
      Alex: "Jon is subclavius of our group."
      Jon: "Wow low blow guys."
Actions: Not much, helps in respiration.
Origin: Border of the 1st rib and its costal cartilage
Insertion: Inferior surface of the middle third of the clavicle
Nerve Supply: Nerve to the Subclavius (C5, C6)

Doesn't bring a lot to the table

The Pectoral Girdle 2: Joints and Ligaments

Next we will discuss some of the joints and ligaments associated with the clavicle and scapula.  A little background is necessary first, though truly getting into joints and ligaments is not the focus of this, if you are interested in more information I am sure google can help you more than me. A joint can have one of two properties, it can be stable or it can be mobile.  These properties are inverses, when one goes up, the other goes down. There are various ways to group joints and most of them deal with the histological characteristics, meaning what types of tissues and cells they present under a microscope.  Three main categories are fibrous, cartilaginous, and synovial joints.
 

Fibrous joints are joined by dense fibrous connective tissue (DICT), a histological term, and usually do not permit movement; an example would be the Lamboid Suture found in the skull between the parietal and occipital bones, think of how the skull is made to fit tightly together and not permit movement between the bones.  Cartilaginous joints are joined by cartilage, at least initially, but may ossify, that is, turn into bone, osseo- is the Latin prefix meaning bone.  This joints allow a tiny bit of movement but not much.  An example is the sternocostal joint between the sternum and the of the first rib.  A related term that means about the same thing is synchondrosis; note the chon in the middle which denotes cartilage (more depth here is cellular and the field of histology). A synovial joint, also known as a diarthrosis, is the most movable and most common type of joint.  An example is the glenohumoral joint (the one that connects your arm to your shoulder and lets you move it around with a high degree of mobility).  The main characteristic of the synovial joint is an encapsulated space filled with synovial fluid which acts like oil in a car engine keeping everything lubricated and running smoothly and without friction.  Again these are just the basics and should be discussed further in histology but they will serve for our purposes.  And onward to the first big joint...

The sternoclavicular joint is classified as a synovial joint but is unique because unlike the standard mobile  synovial joints, this one does not want to move.  It joins exactly what it is named for, the sternum (specifically the manubrium which is the upper part of the sternum) and the proximal end of the clavicle (specifically an indent on the end of the bone called the sternal facet (facet comes from the french word facette meaning little face) .  The sternoclavicular joint has six major components:

1.    Articular Capsule

2.    Anterior Sternoclavicular Ligament

3.     Posterior Sternoclavicular Ligament

4.     Interclavicular Ligament

5.     Costoclavicular Ligament

6.     Articular Disk
Refer to picture below as you read the following...

It is helpful to think of this joint as a very strong junction.  In fact, when subjected to extreme forces, the clavicle will usually fracture before this joint gives out, but there is an sternoclavicular joint separation it can be very dangerous as the clavicle will displace either anteriorly, not great, or posteriorly, much worse due to all the important structures located generally behind it.  An articular capsule forms a sealed off area where the two bone meet.  The clavicle bone wants to push out anteriorly due to the forces created by the arm and this joint must resist that.  So, it developed very thick strong ligaments in the front and back, which we call the anterior and posterior sternoclavicular ligaments.  The interclavicular ligament sits directly on top of each clavicle running along the top of the sternum and connecting both.  It can be palpated (felt by touch) as it sits atop the jugular notch of the manubrium, that little dip of bone on the top of your chest that dips downward.  The costoclavicular ligament attaches the clavicle to the first rib, which sits directly below it.  It serves as an extra anchor attaching the clavicle to the rid and giving it extra support.  The articular disk sits in the articular capsule between the bones and acts as a shock absorbing pad.

On the opposite end is the acromioclavicular joint which again connects exactly what it says (see a pattern?), the acromion process of the scapula (a piece of bone that sticks out) with the clavicle.  The joint consists of 6 major components:

1.       Articular Capsule

2.       Articular Disk

3.       Superior Acromioclavicular Ligament

4.       Interior Acromioclavicular Ligament

5.       Coracoclavicular Ligament

a.       Conoid

b.      Trapezoid

Similarly to the sternoclavicular joint, there is an articular capsule and articular disk serving similar functions.  It is technically a synovial joint, due to the capsule and disk, but serves as more of a strut helping to raise the arm above the head. At this distal end of the clavicle the bone is trying to push up and down due to the forces placed on it, so the body strengths the 'up' and 'down' ligaments to prevent that, we name them the superior and inferior acromioclavicular ligaments, and both are strong and thick.  The coracoclavicular ligament spans from the coracoid process (another small piece of bone that sticks out) to the clavicle and is divided into two parts.  The most medial part is the Conoid Ligament and the lateral part, closest to the arm, is the trapezoid ligament.  They are named due to their shape that they generally appear in the body and function to anchor the clavicle to the scapula, similar to the costoclavicular ligament.

When someone has a separated shoulder it happens here, at the acromioclavicular joint.  This is different than a shoulder dislocation, which occurs at the glenohumeral joint.

The third and last big joint is the glenohumeral joint.  Glene is greek for socket or eyeball (among other things) while the suffix -oid means 'form of' and humerus is Latin for shoulder, though you will mainly encounter it as the name of the upper arm bone, the humerus.  The glenohumeral joint is a highly mobile joint that has 5 main components:

1. Articular Capsule

2. Glenohumeral Ligaments

3. Coracohumeral Ligament

4. Coracoacromial Ligament

5. Transverse Humeral Ligament (of Biceps Brachii)

The articular capsule is different than the first two joints discussed, it is indeed encapsulated but there is not an articular disk.  The humerus sits within the glenoid cavity of the scapula, much like a ball in a socket.  This allows it to be freely movable.  It is also much more involved with, and reliant upon, muscles than the first two, you have probably heard of the rotator cuff, a group of muscles involved with moving it.  The glenohumeral ligaments are a large group of ligaments that blend together to form a capsule around the ball and socket joint.  They consist mainly of a superior, middle, and inferior regions but going into more depth is the area of medical specialties.  

The coracohumeral ligament attaches the coracoid process with the humerus (it is also a part of the blending of the glenohumeral ligament).  The coracoacromial ligament is a very interesting ligament, it is an intra-scapular ligament going from the coracoid process to the acromion process.  It provides separation and cushioning for two muscles that travel here, the deltoid on top and the supraspinatous underneath (more later when we cover muscles), and helps prevent them from rubbing against each other (usually rubbing causes friction and bad things in the body).  The transverse humeral ligament holds the a piece of the biceps brachii muscle, the one you can see when you flex your arm, called the tendon of the long head, more later, in place against the bone.  As I previously stated, if the arm pops out it becomes dislocated.  A term often associated is luxation, which simply means it popped out but not all the way.  

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