Hello anatomy friends this is Dr Alsup  and in this video we will be discussing  
Hello anatomy friends this is Dr Alsup  and in this video we will be discussing  

the deltoid muscle. And I know it seems a bit odd  to just be focused on one muscle in a learning  
the deltoid muscle. And I know it seems a bit odd  to just be focused on one muscle in a learning  

objective video but this is an important one so  we want to spend some time discussing the location  
objective video but this is an important one so  we want to spend some time discussing the location  

innervation and of course the  actions associated with the deltoid.  
innervation and of course the  actions associated with the deltoid.  

So my guess is that even if you  have never had anatomy before  
So my guess is that even if you  have never had anatomy before  

or musculoskeletal anatomy you likely have a vague  idea of where the deltoid muscles are located.  
or musculoskeletal anatomy you likely have a vague  idea of where the deltoid muscles are located.  

Sometimes when associated with exercise  you may hear this referred to as your "delts".  
Sometimes when associated with exercise  you may hear this referred to as your "delts".  

I often lovingly refer to it as your "thick  shoulder cap". It sits superficial too and covering  
I often lovingly refer to it as your "thick  shoulder cap". It sits superficial too and covering  

the glenohumeral humeral or shoulder joint and  it's really that muscle that gives the shoulder  
the glenohumeral humeral or shoulder joint and  it's really that muscle that gives the shoulder  

region the distinct rounded contours that are  visible. So if you put your hand over your shoulder  
region the distinct rounded contours that are  visible. So if you put your hand over your shoulder  

and palpate you can feel your deltoid muscle  deep to the skin and subcutaneous tissue.  
and palpate you can feel your deltoid muscle  deep to the skin and subcutaneous tissue.  

Approximately this muscle has an attachment  and we're looking at a posterior view here  
Approximately this muscle has an attachment  and we're looking at a posterior view here  

you can tell because you can see the majority  of the scapula, so approximately this muscle  
you can tell because you can see the majority  of the scapula, so approximately this muscle  

has an attachment to the bones of the  pectoral girdle so both the clavicle  
has an attachment to the bones of the  pectoral girdle so both the clavicle  

as well as the scapula specifically on  the acromion and the spine of the scapula.  
as well as the scapula specifically on  the acromion and the spine of the scapula.  

And the distal attachment is actually on the shaft  of the humerus and a region referred to as the  
And the distal attachment is actually on the shaft  of the humerus and a region referred to as the  

deltoid tuberosity. So this muscle crosses and can  directly affect the actions of the glenohumeral  
deltoid tuberosity. So this muscle crosses and can  directly affect the actions of the glenohumeral  

joint to that shoulder joint. So speaking of  actions let's explore this a little bit more.  
joint to that shoulder joint. So speaking of  actions let's explore this a little bit more.  

And what I want you to take away regarding  deltoid actions is that it is the primary abductor  
And what I want you to take away regarding  deltoid actions is that it is the primary abductor  

of the shoulder joint so pulling the  arm away from anatomical position in  
of the shoulder joint so pulling the  arm away from anatomical position in  

the coronal or frontal plane so think  lifting your arm to point to the side.  
the coronal or frontal plane so think  lifting your arm to point to the side.  

So by far the most powerful and primary abductor  of the shoulder but it needs a little help at  
So by far the most powerful and primary abductor  of the shoulder but it needs a little help at  

the beginning of the movement so initiating the  action of abduction and it gets that through the  
the beginning of the movement so initiating the  action of abduction and it gets that through the  

contraction of the supraspinatus muscle which is  one of the rotator cuff muscles it will be located  
contraction of the supraspinatus muscle which is  one of the rotator cuff muscles it will be located  

in this general region right here we'll  talk more about that in upcoming videos.  
in this general region right here we'll  talk more about that in upcoming videos.  

Now I do want to note that the deltoid  is actually pretty complex in composition  
Now I do want to note that the deltoid  is actually pretty complex in composition  

it has three separate parts that can contract  independently, and those different parts can  
it has three separate parts that can contract  independently, and those different parts can  

actually produce movements that are antagonistic  or opposing actions, so one part can oppose the  
actually produce movements that are antagonistic  or opposing actions, so one part can oppose the  

action of the other, so you can have flexion as  well as extension and medial or internal rotation  
action of the other, so you can have flexion as  well as extension and medial or internal rotation  

as well as lateral and external rotation dependent  on which part of the muscle is contracting.  
as well as lateral and external rotation dependent  on which part of the muscle is contracting.  

So if you look at the movements that are possible  with contracting or with contraction of the  
So if you look at the movements that are possible  with contracting or with contraction of the  

different parts of the deltoid it actually is  capable of almost every type of action possible  
different parts of the deltoid it actually is  capable of almost every type of action possible  

at the shoulder joint except for adduction. So you  can see how hugely important this muscle is to the  
at the shoulder joint except for adduction. So you  can see how hugely important this muscle is to the  

shoulder region. I do want to note that no muscle  works in a vacuum. Typically multiple muscles are  
shoulder region. I do want to note that no muscle  works in a vacuum. Typically multiple muscles are  

working in unison to produce an action so there  are almost always more than one muscle that can  
working in unison to produce an action so there  are almost always more than one muscle that can  

play a role in a specific action so there'll  be more than one muscle that produces flexion  
play a role in a specific action so there'll  be more than one muscle that produces flexion  

at the shoulder joint or extension. However  there is typically a prime mover or most  
at the shoulder joint or extension. However  there is typically a prime mover or most  

powerful muscle for certain actions and this  can change based on positioning of the joint  
powerful muscle for certain actions and this  can change based on positioning of the joint  

or other factors but really the deltoid is almost  always and I would almost err on saying always the  
or other factors but really the deltoid is almost  always and I would almost err on saying always the  

prime mover in terms of abduction of the shoulder  joint past the first 15 degrees of that movement.  
prime mover in terms of abduction of the shoulder  joint past the first 15 degrees of that movement.  

Another important relationship we want you to  walk away with is the fact that the deltoid muscle  
Another important relationship we want you to  walk away with is the fact that the deltoid muscle  

is innervated by the axillary nerve so one of  those terminal branches of the brachial plexus.  
is innervated by the axillary nerve so one of  those terminal branches of the brachial plexus.  

And this nerve is located deep to the muscle so  you can see the deltoid muscle has been reflected  
And this nerve is located deep to the muscle so  you can see the deltoid muscle has been reflected  

and you can see the axillary nerve right there.  If there's an injury or damage to the axillary  
and you can see the axillary nerve right there.  If there's an injury or damage to the axillary  

nerve this can affect the deltoid muscle and  potential for movements associated with that  
nerve this can affect the deltoid muscle and  potential for movements associated with that  

and it can even lead to atrophy  of the muscle if severely damaged.  
and it can even lead to atrophy  of the muscle if severely damaged.  

One thing also to note the deltoid muscle  is a notably thick and coarse fibered muscle  
One thing also to note the deltoid muscle  is a notably thick and coarse fibered muscle  

and because of this in its superficial location  it's a common site for intramuscular injections.  
and because of this in its superficial location  it's a common site for intramuscular injections.  

And so because of that you need to be aware  of the location of that axillary nerve  
And so because of that you need to be aware  of the location of that axillary nerve  

deep to the muscle and taking care to avoid  the axillary nerve in its more posterior position.
deep to the muscle and taking care to avoid  the axillary nerve in its more posterior position.

Excellent so that is the deltoid muscle in a  nutshell, those big picture concepts we want  
Excellent so that is the deltoid muscle in a  nutshell, those big picture concepts we want  

you to walk away with. I hope you take time  to review this and always feel free to reach  
you to walk away with. I hope you take time  to review this and always feel free to reach  

out with any questions. Thank you for your time  and attention and have a great rest of your day
out with any questions. Thank you for your time  and attention and have a great rest of your day