Shoulder/Arm Anatomy Flashcards
What are the factors that affect the amount of force a muscle exerts at a joint axis?
Size/Bulk of a muscle (Cross-sectional area)
Shape of a muscle: straight or penate or something
angle of pull relative to the axis
Insertion site close to or far away from joint
What is a straight muscle good for? What is a penate or bipenate muscle good for?
Straight Muscle: great ability to change in length
Bipenate or penate muscle: supplies more power, less ROM
When a muscle is attached close to the joint…it is good for? When it is attached far away?
Close to the joint: speed
Far from the joint: power
All muscles help to stabilize the joint they _____.
the joint they cross
In general, the upper extremity is good for speed/power & the lower extremity is good for speed/power.
Upper Extremity: Speed
Lower Extremity: Power
What are the 3 things you must ask yourself when you look at a new muscle?
What are the axes this muscle exhibits? What are its possible actions? Where does the muscle cross the joint relative to the axis?
Describe how the upper limb is stabilized.
What is crazy about the upper limb is that the only bone attachment to the axial skeleton/stabilization is the sternoclavicular joint. The rest is just muscle stabilization. This is why it is so freely moveable.
Why is it important that the inferior angle of the scapula can move laterally & medially?
b/c this allows for full abduction of the scapula.
What is the shape of the clavicle? What is the superior side like? What is the inferior side like?
S-shaped clavicle
Superior side is smooth
Inferior side is rough so that ligaments can attach to it.
T/F The clavicle is a common bone to fracture.
TRUE
What is the origin of the clavicle?
membranous origin
What are 2 fun bone facts of the clavicle?
- first long bone to ossify: weeks 5-6
2. last long bone to fuse @ epiphyseal plate around 25 years
How does the clavicle ossify?
intramembranous ossification
a little endochondral ossification maybe
What are the 2 joints that the clavicle is a part of?
sternoclavicular joint
acromioclavicular joint
What are 2 possible actions of the shoulder girdle?
shoulder shrug: elevation/depression
Protraction/Retraction (along the vertical axis)
During protraction/retraction of the scapula…what must happen to the scapula?
It must glides along the chest wall with 15 degrees worth of gliding movement
Movements of the shoulder girdle require some mobility of the ____ joint.
AC joint
Which ligaments stabilize the acromioclavicular joint (AC)?
Mainly: coracoclavicular ligaments
Maybe sorta: coracoacromial ligament
What are the 2 ligaments that make up the coracoclavicular ligaments? Where are they located?
trapezoid ligament (more lateral) conoid ligament (more medial)
What is the function of the coracoacromial ligament?
it forms the roof of the glenohumeral joint–>this is where the head of the humerus rests!!
Where does the clavicle usu fracture?
usu in the middle & distal 3rd
**usu just proximal to the coracoclavicular ligaments
What is the difference b/w shoulder separation & shoulder dislocation?
shoulder separation: occurs at the AC joint
shoulder dislocation: occurs @ the glenohumeral jt
T/F You cannot separate the AC joint w/o tearing the coracoclavicular ligaments, as they are a strong stabilizing force.
FALSE. You can separate the AC jt w/o tearing the ligaments. It consists of just a broken clavicle, distal to the ligaments.
Often though, you break the clavicle & tear the ligaments.
Describe shoulder dislocation.
the head of the humerus is forced out of the glenoid fossa
What direction is the head of the humerus usu pushed in when you experience a shoulder dislocation?
usu anteriorly & inferiorly.
Describe a physical position that would make it easier to dislocate your shoulder. Why is this such a vulnerable position?
when your arms are fully abducted above your head…if someone came from behind & smacked your shoulder.
vulnerable b/c the head of the humerus in this position isn’t in contact w/ the glenoid fossa…when articular surfaces aren’t touching called a loose packed jt & is more vulnerable…once it is dislocated…muscles contract, forcing the head of humerus into the axillary fossa.
What is the glenoid labrum & how does it relate to shoulder dislocation?
this is an extension of cartilage that is found in the shoulder. It is easy to tear during shoulder dislocation.
How can you put a shoulder back into its socket after shoulder dislocation?
if you have had multiple dislocations, maybe you can just pop it back…usu need muscle relaxants & a doctor’s assistance.
Describe the sternoclavicular joint.
It is a synovial joint w/ 2 synovial cavities and a fibrocartilage articular disc.
Describe the ligaments surrounding the SC joint.
sternoclavicular ligament costoclavicular ligaments (clavicle-->ribs)
Describe all the possible movements of the SC joint & their axes.
Elevation/Depression –AP Axis
Retraction/Protraction–Vertical Axis
Medial/Lateral rotation–Oblique Axis
What defines lateral or medial rotation @ the SC joint?
lateral or medial rotation of the inferior angle of the scapula
If you had a muscle that was attached around the neck/head area & attached to the superior angle of the scapula (levitator scapulae)…what would contracting this muscle do on the AP axis & the oblique axis?
AP axis: options are up & down. It would pull the scapula up.
Oblique axis: options are lateral & medial rotation. It would cause medial/internal rotation.
Describe the 2 things that are required for full abduction of the arm.
Can achieve 120 degrees of abduction via the glenohumeral joint.
Achieve the other 60 degrees of abduction via the sternoclavicular joint.
Combination of the 2 is called scapulohumeral rhythm.
If you want to help out your arm in its abduction efforts…what is the best position to put it in? What is the worst position-why?
Best position: laterally rotated
Worse position: medially rotated b/c the greater tubercle of the humerus will hit the acromion.
What is the primary abductor of the arm?
deltoid muscle
Where does the trapezius medially attach?
spinous processes of vertebrae
&& superior nuchal line of the head
The trapezius muscle kind of has 3 parts. What are these different sections & in what direction do their fibers run?
Superior: fibers run inferolaterally
Intermediate: fibers run straight laterally
Inferior: fibers run superolaterally
Where is the oblique axis located relative to the trapezius muscle? What direction does the oblique axis run?
it is located beneath the superior & intermediate sections of the trapezius & superior to the inferior section.
**it runs anteromedially to the SC joint
T/F The trapezius muscle is an upper limb muscle that is innervated by the brachial plexus.
FALSE
It IS an upper limb muscle.
It is NOT innervated by the brachial plexus. But by a cranial nerve.
Which cranial nerve supplies the trapezius muscle?
Cranial nerve 11, the spinal accessory nerve supplies the trapezius.
If something happened to the brachial plexus…what would happen to upper limb muscles?
They would be in trouble! Except for the trapezius b/c it is innervated by cranial nerve 11, and not the brachial plexus.
If you were to briefly describe the brachial plexus, how would you describe it?
ventral rami of spinal nerves
What are the actions of the superior, intermediate, and inferior portions of the trapezius muscle on the following axis?
Vertical Axis?
All sections of the trapezius muscle retract on the vertical axis. It makes sense b/c they all attach medially in the back. When they shorten, they encourage retraction.
What are the actions of the superior, intermediate, and inferior portions of the trapezius muscle on the following axis?
AP axis?
Superior: Elevates
Intermediate?
Inferior: depresses
What are the actions of the superior, intermediate, and inferior portions of the trapezius muscle on the following axis?
Oblique axis?
all 3 laterally rotate
Does the trapezius act as a unit or as 3 separate parts?
depends…
when working on the vertical or oblique axis, it works as a unit, b/c they all accomplish the same thing.
when working on the AP axis, it works as individual parts b/c they accomplish different actions.
What supplies motor innervation to the trapezius muscle? What supplies proprioceptive innervation–so that you know what level of contraction that muscle is under?
Motor innervation: spinal accessory nerve (cranial nerve 11)
Proprioception: C3, C4 cervical segments (these little guys jump onto CN 11).
Describe the location of the latissimus dorsi muscle.
it is attached to the inter tubercular groove (b/w the greater & less tubercle of the humeral head)
it then runs horizontally & is attached to the thoracolumbar fascia.
What are the joints that the latissimus dorsi muscle acts on?
Mainly: glenohumeral joint
Also (if glenohumeral joint is stabilized): sternoclavicular joint
What are the actions of the latissimus dorsi muscle @ the glenohumeral joint? What is the axis of these actions? What types of sports does this support?
Extends & Medially rotates & adducts Extension on the transverse axis. Medial Rotation on the vertical axis Adduction on the AP axis **good for swimming & rock climbing
What are the actions of the latissimus dorsi @ the SC joint when the glenohumeral joint is stabilized?
retraction & depression of the shoulder girdle
What is the nerve supply to the latissimus dorsi muscle?
thoracodorsal nerve aka middle sub scapular nerve
**found on the posterior cord of the brachial plexus
T/F The latissimus dorsi is a deep back muscle.
False. It is superficial & extrinsic.
T/F The latissimus dorsi passes medial to the vertical axis.
true. I have no idea why.
What are some superficial back muscles that act on the scapula?
trapezius
rhomboids major & minor
levator scapulae
What joint does the rhomboid major & minor work @? What is its action there? Which axis?
Works @ the SC joint
retracts & medially rotates the scapula
retraction is on the vertical axis
What does it really mean that the rhomboids medially rotate the scapula upon contraction?
it means that if you look @ the inferior angle of the scapula…it is pulled inward with contraction. It is pulled medially as the scapula is retracted.
What is the nerve supply to the rhomboid major & minor?
dorsal scapular nerve
this is a part of the brachial plexus coming off of C5.
Where is the levator scapulae located?
it is connected to the transverse processes of the cervical vertebrae & it runs down to the superior angle of the scapula
What is the action of the levator scapulae?
It elevates & medially rotates the scapula.
What is the nerve supply to the levator scapulae?
dorsal scapular nerve
What are some anterior muscles that affect the SC joint?
pectoralis minor muscle
serratus anterior muscle
What is the pec minor muscle attached to?
coracoid process
What is the innervation of the pec minor?
medial pectoral nerve (also innervates the pec major)
What actions does the pec minor do @ the SC joint–that is, what does it do to the shoulder girdle?
depresses (AP axis)
protracts (vertical axis)
medially rotates (oblique axis)
What is the location of the serratus anterior? Aside from its SC joint function, what is its other function?
it is on the anterior surface of the body, connected to ribs & a part of the scapula.
next to the subscapularis
**holds the scapula tight against the body wall, keeps it from popping out when you push against something.
What are the actions of the serratus anterior on the shoulder girdle @ the SC joint?
Depresses (AP axis)
Protracts (vertical axis)
Laterally Rotates (Oblique axis)
What is the innervation of the serratus anterior?
long thoracic nerve (this comes from the roots of the brachial plexus)
it is located superficially to the muscle which is unique & makes it more prone to damage.
What happens if you damage the long thoracic nerve of the serratus anterior?
you can get winging of the scapula
At the SC joint, what can cause protraction?
serratus anterior
pec minor
At the SC joint, what can cause retraction?
trapezius (middle portion)
rhomboid major
rhomboid minor
At the SC joint, what can cause elevation?
trapezius (upper part)
levator scapulae
rhomboid major
rhomboid minor
At the SC joint, what can cause depression?
serratus anterior
pec minor
trapezius (lower part)
At the SC joint, what can cause medial rotation?
pec minor
rhomboid major
rhomboid minor
levator scapulae
At the SC joint, what can cause lateral rotation?
trapezius (all parts)
serratus anterior