2.

1
The best way for us to learn about the upper extremity is to begin at the very beginning,
right up here. We'll start by looking at the bones of the shoulder. Region the clavicle. The
scapula and the humerus. Then we'll look at the joints which let them move and at the
muscles which make them move. Lastly, we'll look at the principal blood vessels and nerves
in the region. First the bones. The bones that connect the upper extremity to the trunk are
the clavicle or collarbone. And the scapula or shoulder blade. The parts of them that we can
feel beneath the skin can be seen in this dissection. Here's the spine of the scapula. Here's
the clavicle. In the dry skeleton, here's the clavicle. Here's the scapular. The proximal long
bone of the upper extremity. The humerus articulates with the scapula at the shoulder joint.
The scapula and clavicle articulate with the bones of the thorax at 1:00 point only here. At
the Sternoclavicular joint. The lateral end of the clavicle articulates with this projection on
the scapula, the acromion forming the acromioclavicular joint. Apart from this one very
movable Bony linkage, the scapula is held onto the body entirely by muscles. It's this
capable of a wide range of movement. Upward. And downward. And also forward and
backward around the chest wall. Looking at the clavicle from above, we can see that it's
slightly S shaped with a forward curve to its medial half. At its medial end, this large joint
surface articulates with the sternum. At the lateral end, this smaller surface articulates with
the scapula. And the underside. Massive ligaments are attached. Here laterally. And here
immediately. The scapula is a much more complicated bone. The flat part or blade is
roughly triangular with an upper border. A lateral border and a medial border. The blade
isn't really flat, it's a little curved to fit the curve of the chest wall. This smooth concave
surface is the glenoid fusser. It's the articular surface for the shoulder joint. Above and
below the glenoid fossa are the supraglenoid tubercle. And the infraglenoid typical where 2
tendons are attached, as we'll see. A prominent Bony Ridge, the spine of the scapula, arises
from the dorsal surface. And divides it into the supraspinous fossa. And the infraspinous
fossa. At its lateral end, the spine gives rise to this flat angulated projection. The acromion,
which stands completely clear of the bone. The clavicle articulates with the scapular. Here
at the tip of the acromion. This other projection looking like a bent finger is the coracoid
process. Here's how the clavicle and the scapular look in the living body. Round the edge of
the shallow glenoid fossa, a room of fibrocartilage that glenoid labrum makes the socket of
the shoulder joint both wider and deeper. This flat ligament, the coracoacromial ligament,
joins the coracoid process to the acromion. Here's the Acromioclavicular joint 2 strong
ligaments, the trapezoid in front and the coronoid behind fixes the underside of the clavicle
to the coracoid process. There's very little movement at the Acromioclavicular joint. As
we've seen, the medial end of the clavicle articulates with the sternum at the
sternoclavicular joint. Strong ligaments between the clavicle and the sternum. And between
the clavicle and the underlying first rib. Keep the 2 bones together, but permit an
impressive range of motion. Up and down. And backward and forward. Now let's see how
the clavicle and the scapula move relative to the trunk. Upward movement of the scapular
is called elevation. Downward movement is called depression. Forward movement around
the trunk is called protraction. The opposite movement is retraction. This movement is
called upward rotation. The opposite movement is downward rotation. In real life, these
movements of the scapular are often combined. The range of motion of the scapula
provides fully 1/3 of the total range of motion of the humerus relative to the body,
sometimes more. Without this movement of the scapula, we'd only be able to abduct our
arm to hear. That's as far as the shoulder joint goes before bone hits bone. It's scapular
movement that lets us get all the way to here. Now let's look at the shoulder joint. To
understand the shoulder joint, let's get acquainted with the upper half of the humerus. This
is the head of the humerus. The articular surface is half of a sphere. On the anterior aspect
is a well marked groove known as the bicipital groove because the tendon of the long head
of the biceps runs in it at the proximal end of the groove are the lesser tubercle and the
greater tubercle. Because it's between 2 tubercles. The bicipital groove is also known as the
intertubercular groove. Don't hear on the lateral aspect of the humerus, almost halfway
down the bone is a rough spot. The deltoid tuberosity. Here's the shoulder joint, also known
as the Glenohumeral joint. This loose sleeve of tissue which encloses the joint is the joint
capsule. The capsule doesn't hold the bones together. It's quite a weak structure. What it
does is to permit movement the structures which hold the 2 bones together are muscles, as
we'll see here is the tendon of one of those muscles. Let's look at the movements that can
occur at the shoulder joint. Movement forward and upward is called flexion. Movement
downward and backward is called extension. Movement away from the side of the body is
abduction. The opposite movement is abduction. Rotation, which moves the front of the
arm towards the body, is internal rotation. Rotation the other way is external rotation.
Communication.
Now that we've taken a look at the bones, joints and ligaments, let's spend about a minute
reviewing what we've seen so far. Here's the clavicle for an easy start. On the scapular,
here's the blade, the glenoid fossa, the supraglenoid and infraglenoid cubicles. The spine of
the scapula. The Supraspinous and Infraspinous fossa their chromium. And the coracoid
process. Here's the proximal humerus with the head. The greater tubercle and lesser
typical. The bicipital groove. And the deltoid tuberosity. Here's the sternoclavicular joint.
And here's the acromioclavicular chind with the Kennard ligament. And the trapezoid
ligament. On the scapular, here's the glenoid labrum. And the coracoacromial ligament.
Lastly, here's the capsule of the shoulder joint. Now let's move on to look at the muscles.
We'll build our understanding pretty much from the inside to the outside. First, we look at
the deepest muscles, the ones that go from the scapula to the humerus. Then we'll look at
the ones which go from the trunk to the scapula. And lastly, we'll look at the big 3 muscles
on the outside, which cover up almost all the. Others. Before we look at any shoulder
muscles, we need to take note of the tendons of 2 long elbow muscles which arise very
close to the shoulder joint and lie deep to everything else. They're the tendons of the long
head of the biceps. And the long head of the triceps muscles. The long head of transepts
arises here from the infraglenoid tubercle. The long head of biceps arises surprisingly here
from the supraglenoid tubercle. To get there, it passes inside the joint capsule and right
over the top of the head. Of the humerus. Now let's look at the 4 short muscles which hold
the shoulder joint together. There are 3 on the back. One on the front. The one on the front
is subscapularis. It arises from almost all of the anterior or coastal aspect of the scapula. Its
tendon inserts here on the lesser tubercle. Subscapularis acting alone produces internal
rotation of the humerus. Acting with the other 3 short muscles, it holds the humeral head
and the glenoid fossa together, while other more powerful muscles are at work. On the back
there are 2 muscles below the scapular spine and one above it. The one above is
supraspinatus. It arises from almost all of the supraspinous fossa. It passes under the
acromion. And inserts here on the greater cubicle. The tendon of supraspinatus runs
through a tight spot. Between the acromion and the head of the humerus, there's a synovial
lined pocket. A Bursa here between it and the acromion. Super. Pinnatus initiates abduction
of the humerus. The 2 muscles below the spine are infraspinatus. And terrace minor.
Between them, they arise from almost all of the infraspinous fossa infraspinatus here.
Terrace minor here. Infraspinatus inserts here on the back of the greater tubercle terrace
minor just below it. Both these muscles produce external rotation of the humerus. These 4
short muscles subscapularis supraspinatus. Infraspinatus and teres minor converge on the
humerus to form an almost continuous cuff of flat supporting tendons, often referred to as
the rotator cuff. It's these tendons together with the long head of the triceps down here,
which keeps the head of the humerus from sliding out to its very shallow socket. There are
2 other muscles to note that also run from the scapula to the humerus, one on the front and
one on the back. The one on the back is Terrace Major. It arises here from the lower lateral
border of the scapula and inserts here on the Crest of the lesser tubercle. Terry 's Major is
quite a powerful and doctor of the humerus. On the front, here's coracobrachialis. It arises
from the coracoid process. It inserts down here on the humerus. Koraka brachialis helps to
flex the shoulder joint. Altogether, there are 7 muscles that go from the scapula to the
humerus, and so far we've seen 6 of them. The last one that deltoid is so big that it covers
up almost everything else, so we'll leave it out of the picture till the very end. Now it's time
to look at the muscles which hold the scapular in place and move it in relation to the trunk.
There are 6 of them, 4 on the back, 1:00 in the front and one underneath. The one on the
underneath is the large and powerful serratus anterior muscle. This is just part of it. To see
it all, we need to move the scapula away from the body. Big expense of muscle is all
serratus anterior. It arises from the side and front of the first 8 ribs. It runs back under the
scapula. And it's inserted all the way back here, along the medial border of the scapula.
When the holds serratus anterior muscle contracts, it pulls the scapula forward around the
rib cage that's protrusion. When it's upper. Or lower fibers contract separately. They help to
produce downward. Or upward rotation of the scapula. Now let's look at those 4 muscles on
the back. One, the trapezius is large and superficial. The other 3 are small and deep. The 3
deep ones are levator scapulae and the 2 rhomboids rhomboid minor and rhomboid major.
Levator scampy arises here on the outermost point of the first 3 cervical vertebrae. It
inserts here on the upper medial corner of the scapula. Levator scapulae helps to elevate
the scapula. The rhomboids arise here from the 4th cervical to the 5th thoracic vertebrae.
They insert here, along the medial border of the scapula. The rhomboids elevate and retract
the scapula. The large muscle which overlies these 3 is the trapezius. It's a beautiful but
complicated muscle. The trapezius has an upper part. And a lower part which both
converge on the spine of the scapula. The upper part of trapezius arises from the occiput.
And from the nuchal ligament and from T one to 3:00 in the midline. It's inserted along the
upper edge of the spine of the. Scapula. Around the acromion and along the lateral 3rd of
the clavicle. The lower part of the trapezius muscle is not so massive. It arouses from T 4.
To 12:00 in the midline. It inserts here on the lower edge of this part of the spine of the
scapula. When the whole of trapezius contracts, it powerfully retracts the scapula. When
the upper part contracts, it powerfully elevates the scapula. Last on the list of muscles
passing from the trunk to the scapula. Is the one on the front. It's pectoralis minor.
Pectoralis minor arises between the second and the 4th ribs. It's inserted on the coracoid
process. Pectoralis minor produces depression of the scapula. There are 2 very small
muscles to mention just for completeness. One is subclavius which goes from the first rib to
the clavicle. Its function is uncertain. The other is omohyoid, which arises from the hyoid
bone way up here. And inserts over here. On the upper edge of the spine of the scapula. Its
function is to depress the hyoid bone and the larynx. Now we'll complete our picture by
looking at 3:00 big external muscles pectoralis major latissimus dorsi, and deltoid. Of these,
the first 2 have much in common. Pectoralis major on the front. And latissimus dorsi on the
back. These 2 are alike and that they both pass directly from the trunk to the humerus.
Bypassing the scapula. Between them, they define the posterior and anterior walls of the
axilla. Pectoralis major arises from the medial 3rd of the clavicle. From the front of the
sternum. And from the front of the first 6 coastal cartilages. It's inserted here on the
anterior edge of the bicipital groove. Pectoralis Major is a powerful abductor of the humerus
when its abducting effect is held in check by other muscles. It also produces internal
rotation. Latissimus dorsi has a very wide origin. It starts here under the tail end of
trapezius, at T 7 and goes all the way down to the sacrum. And out onto the posterior iliac
Crest. It also has some fibers arising from the lower 4 ribs and occasionally from the tip of
the scapula. It inserts here. On the posterior edge of the bicipital groove. To get to its
insertion, the latissimus tendon has to spiral around Teryx major. Here's Teryx major
latissimus spirals from the back. To the front with the lowest fibers of origin ending up
highest. Latissimus dorsi, like pectoralis major, is a powerful abductor of the humerus.
Acting through the humerus, it's also a powerful depressor of the scapular, powerful enough
to overcome the whole weight of the body, as in doing a push up. Last of all. Here's the
deltoid muscle. It completely surrounds the shoulder joint from the front. To the back. It
arises from the spine of the scapula. From the acromion and from the lateral 3rd of the
clavicle. It's inserted here on the deltoid tuberosity of the humerus. The deltoid muscle has
multiple functions. It's almost like 3 different muscles. Its anterior part is a powerful flexor.
Its posterior part is a powerful ex tensor. And its lateral part is a powerful abductor. Now
that we've seen all the muscles which act on the scapula and on the proximal humerus,
let's review them. If you want to test yourself. Turn off the sound. Here is subscapularis.
Supraspinatus. Infraspinatus. And Terry 's minor. He is terrye major. And coracobrachialis.
Now the muscles that arise from the trunk. Serratus anterior. Levator scapulae. The 2
Roombots minor and major. Trapezius. Pectoralis minor. Subclavius and omohyoid. And
lastly. Pectoralis major. Pessimist Dorsey. And deltoid. We've covered a lot of ground. I
suggest you take a break before you watch the rest of the day. Switch off for a while and
start again in a few minutes. Now let's look at the veins, arteries and nerves of the shoulder
region. As you will see, the main bundle of vessels and nerves lies behind the clavicle and
behind both pectoral muscles as it passes from the base of the neck to the underside of the
upper arm. To understand how things are arranged up here, where the main vessels come
up out of the chest and the main nerves emerge from the vertebral column, there are some
key structures that we need to understand the first ribs. The cervical vertebrae and the
scalene muscles. Let's take a look at them. Here's the first rib. Below and behind the
clavicle. This much of it is bone. And this much of it is coastal cartilage. The 2 first ribs
define the opening at the top of the chest. The superior thoracic aperture. The main artery
to the upper extremity, the subclavian artery crosses the first rib here. The subclavian vein
crosses it here, right behind the medial end of the clavicle. Here are the vertebrae, the first
thoracic with the first rib. And the 7th, 6th and 5th cervical. Let's take the clavicle away so
that we can see the vertebrae better. The main spinal nerves to the upper extremity
emerge here between the transverse processes, the spinal nerves that we're concerned
with are numbered C 5, C 6, C 7, C 8. And T one. These 2 landmark muscles, the anterior
scalene and the middle scalene. Which are attached to the first rib here. And here guard
the exit of these vital structures. The vein runs in front of the anterior scalene, the artery
runs behind it. Between the 2 scalene muscles, the roots of the brachial plexus also
emerge. There are 2 possibly confusing things that we have to live with. The first is that
there's a nerve root named C 8, even though there's No 8 cervical vertebra. The second
confusing thing is that the main artery and vein change their names as they go along. Here
they're called the subclavian vessels. Here they're called the axillary vessels. And from here
on down, they're called the brachial vessels. The structures themselves don't change, just
the names. Let's start by looking at the veins. We can be quite brief about this since the
veins parallel the arteries in most important respects. It will be helpful to start on the
outside and progress inward, removing some muscles as we go along. Here in the groove
between pectoralis major and deltoid is the cephalic vein coming up from the arm? It's a
vein that doesn't have an accompanying artery. To see where it's going, we'll remove
pectoralis major. Here's the cephalic vein. Together with other veins from the shoulder
region, it joins the main vein of the upper extremity, the subclavian vein. We'll focus our
attention on this important vein. The subclavian vein comes up from the arm and passes
beneath pectoralis minor. Emerging from beneath pectoralis minor, it passes over the outer
surface of the first rib. Here's the first rib, and under the subclavius muscle and the clavicle.
To follow the subclavian vein further, we'll remove the clavicle, the subclavius muscle, and
this muscle, the sternocleidomastoid. Here we are, behind the medial end of the clavicle.
Which went from here. This is the cut end of the clavicle. To here. This was the
Sternoclavicular joint. Here's pectoralis minor. Here's the curve of the first rib. These
structures, the subclavian artery and the brachial plexus we'll be seeing in a minute. Let's
follow the vein. Just as the subclavian vein reaches the medial border of the first rib which
is here, it's joined from above by the main vein of the head and neck. The internal jugular
vein. Together, the subclavian and internal jugular veins form the brachiocephalic vein. The
Brachiocephalic vein passes medial to the first rib and enters the chest. The Dome of the
pleura lies immediately behind it. Here's the plura. To follow the Brachiocephalic vein into
the chest. We'll remove these muscles. And will also remove. This part of the anterior chest
wall. We'll also remove the other clavicle. Now we're looking inside the chest. Here are the
divided ends of the 2 first ribs. And here's the divided end of the sternum. Here are the 2
brachiocephalic veins the right. And the left. A little to the right of the midline, they join
together to form the superior phena cava. Apart from what we've just seen, the veins of the
region correspond so closely to the arteries that we don't need to consider them separately.
We'll move on now to look at the arteries. In the dissections that follow all the
accompanying veins have been removed to simplify the picture. To get a good look at the
artery as it runs from here. To here we need to remove pectoralis major. Now only 3
structures stand between us and it. Here's the artery. Passing behind the anterior scalene
muscle. Behind the clavicle. And behind pectoralis minor. 3 names for one artery
subclavian. Accelerate. Brachial. Let's see where it begins. Here's a deeper dissection with
the chest wall removed. Here are the divided ends of the clavicle. The first rib with the
anterior scalene muscle. And the second rib. In the middle, we're looking at the trachea.
And the common carotid arteries the right. And the left. On the right side, the subclavian
artery arises along with the common carotid from the brachiocephalic trunk, which in turn
arises from the arch of the aorta. On the left side, the subclavian artery arises directly from
the arch of the aorta. In the early part of its course, as it passes over the Dome of the
pleura, the subclavian artery gives off some major branches, which we'll see in other parts
of the Atlas. These are the internal thoracic. The thyrocervical trunk. And the vertebral? In
addition, the subclavian gives off 2 branches to the back and shoulder region. These are the
transverse cervical and the suprascapular arteries. These 2 are variable. Sometimes they
arise here sometimes here. The main artery. Now called the axillary next, gives off 2
branches behind pectoralis minor. They're the thoracoacromial. And the lateral thoracic
arteries. In the axilla 3 more branches arise, often close together the subscapular. And the 2
circumflex humeral arteries the anterior and the posterior. The posterior circumflex humeral
winds round behind the neck of the humerus. Finally, the artery now known as the brachial
artery passes on down the upper arm. Now let's look at the nerves. Between about here
and here, the 5 spinal nerves unite. And divide. Unite again and divide again the tangle
which this produces is called the brachial plexus. It's not really too formidable at the end of
the brachial plexus, the 4 main nerves of the arm emerge. The musculocutaneous, the
medium, the ulnar, and the radial. In the course of the brachial plexus, the nerves which
supply the shoulder region are given off. We'll look at the main components of the brachial
plexus first, then at the local branches. Here's the brachial plexus, with several of its small
branches removed so we can see the big picture. We will also remove pectoralis minor. Here
are the 5 roots of the brachial plexus. They are in fact the ventral Rami of their respective
spinal nerves. They emerge, as we've seen from between the anterior scalene and middle
scalene muscles. The top 2 roots join. And the bottom 2 join and the middle one C 7 stays
alone. These 3 big units are called the 3 trunks, upper, middle and lower. Each trunk
divides. Here's one of them, dividing into an anterior and a posterior division. Of the 3
anterior divisions, the Upper 2 unite. And the lower one stays alone. The 3 posterior
divisions all unite as we'll see in a minute. Once that's all happened, there are again 3 big
units now called chords, lateral medial. And posterior. They surround the axillary artery. The
lateral cord divides. To become the musculocutaneous nerve. And 1/2 of the median nerve.
The medial cord divides to become the ulnar nerve. And the other half of the median nerve.
This arrangement produces an M shaped pattern of nerves, musculocutaneous, median and
ulnar. Now let's see the posterior cord. We need to remove the medial cord, the lateral cord
and the artery. To get a good look at it. Here's the posterior cord all by itself. Sometimes it
starts dividing before all 3 of its posterior divisions have united. The principal branches are
the axillary nerve. Which we'll see again. And the radial nerve. Now that we've looked at
the main components of the brachial plexus, let's look at the nerves which supply the
muscles of the shoulder region. Some of these arise from the chords of the brachial plexus.
Some arise in other ways. Let's look at the ones that arise from the chords. First, we were
looking at a simplified dissection before. Now we'll see the details. The medial cord gives
rise to one local nerve, the lateral cord, to 2. The one from the medial cord is the medial
pectoral nerve. It's one of a pair. Here's its partner, the lateral pectoral nerve, which arises
from the lateral cord. The pectoral nerve supply pectoralis major. umm Also arising from the
lateral cord is the musculocutaneous nerve. It supplies 3 upper arm muscles, one of which
we've seen coracobrachialis. The other 2 we'll see in the next section. The posterior cord.
Here it is again with all its branches intact. Has 4 branches. The axillary nerve runs around
the neck of the humerus. Along with the posterior circumflex humeral artery. To supply the
deltoid muscle and also teryx minor. The subscapular nerves and upper and a lower supply
subscapularis. And Terry 's major. The thoracodorsal nerve. Supplies latissimus dorsi. Now
let's see the shoulder muscle nerves which don't arise from the chords of the brachial
plexus. Of these, one is the branch of a trunk 2 arise from the roots of the brachial plexus,
and 2 aren't part of the plexus at all. Arising from the upper trunk. Is the suprascapular
nerve which supplies supraspinatus and infraspinatus. Arising from the C 5 root and passing
through the middle scalene muscle is the dorsal scapular nerve. It supplies the rhomboid
muscles. Arising from the C 56 and 7 roots, the long thoracic nerve emerges through the
middle, scaling muscle runs deep to all 3 trunks of the brachial plexus and supplies serratus
anterior. Trapezius gets its nerve supply from the spinal accessory nerve. Lastly, levator
scapulae gets a private nerve supply from the nearby routes of C 34 and 5. We've looked at
some pretty complex and detailed anatomy in the last few minutes. Let's review what we've
seen of the veins, arteries and nerves at the shoulder region. First, the few veins that we
saw. The cephalic. Subclavian. And brachiocephalic veins. Next, the arteries. The
brachiocephalic trunk. The subclavian artery. The axillary artery. The brachial artery. The
transverse cervical. And suprascapular arteries. The thoracoacromial. Lateral. Thoracic.
Subscapular. Anterior. And posterior circumflex humeral arteries. Lastly, nerves starting
with the main components of the brachial plexus. The roots of the brachial plexus. C 5 C 6 C
7 C 8. And T one. The 3 trunks. Upper. Middle.