hello all this is dr. Kathleen Alsup and I am so very excited to begin the course with you with our
first learning objective lecture in these sessions we will explore the concepts in each learning
objective and we will talk through these areas to provide context to what you're reading within the
learning objectives so make sure that you have read through the learning objective text before
viewing these as that will make these sessions much more meaningful and you can really hone in on
the areas that perhaps didn't make as much sense in your initial reading so if you have read the
first learning objective let's get started I am so excited alright this is the text of the first
learning objective and it's covering four main areas we will start by discussing what this odd
word means here what is fascia what does that even mean then we will talk about what muscle or which
muscle is located within the superficial fascia of the neck next we will spend the majority of
our time discussing the three main layers of deep cervical fascia so specific to the neck region as
this is a bit more of a complex area so I want to take this topic nice and slow so this video may be
a little bit longer than the subsequent learning objective lecture videos and kind of throughout
this discussion we will discuss why we are even talking about these layers and the spaces they
form there is always a reasoning behind our making you memorize certain areas so let's start the fun
alright let's begin this discussion with the most superficial layer of the entire body and that is
the skin as this will give us context for all the deeper layers the skin is going to be composed of
the epidermis which is the outer and a vascular layer as well as the dermis which I am outlining
here in red the dermis is the deeper and vascular layer if you have a cut and it is bleeding it has
at least read the dermis or potentially deeper as a cut of the epidermis would not lead have
you ever heard of the joke your epidermis is showing that is how I always remember which
one is the most superficial so epidermis is the most superficial the dermis is deep to
the epidermis but still part of the skin deep to the skin and we get into the fascial layers so
now is the time to define fascia fashion is any grossly visible connective tissue collection or
a sheath deep to the skin so gross here does not mean you gross but visible to the naked eye you
are currently taking a gross anatomy course non histology course with the study of microscopic
tissue so that's what we mean by gross just deep to the dermis is going to be a layer that has many
different names the preferred scientific name is superficial fashion but you will commonly also
here this layer referred to as the hypodermis subcutaneous tissue or just the fatty layer as
as it is composed of loose areolar connective tissue with varying amounts of adipose tissue
so this makes this layer really important in terms of fat storage in a principal site for large blood
vessels that supply and drain the capillaries of the skin so depending on the area of the body and
individual variation of course there is a varying amount of adipose tissue so if you think about in
the head and neck regions in comparison to other areas of the body there's actually comparatively
less adipose tissue in the head and neck region deep to the superficial fascia will be the deep
fascia which you can see here kind of surrounding here this particular one surrounding a muscle the
deep fascia it is organized into multiple layers surrounding muscle viscera which means organs and
as I mentioned this is where we'll spend the majority of our time in this video I like this
image because it really shows the relationship between the superficial fascia which you can see
in this region here and the deep fascia what you can see here and how they look pretty different
based on their composition the superficial fasho generally will have a yellowish kind of brownish
tinge it's going to be less organized in composition whereas the deep fashion is
typically more organized it will appear kind of silver or whitish in appearance or in areas
where it's thinner like an investing fashion it's almost translucent and that's kind of what makes
the muscles or the viscera appear shiny but we aren't talking about the hands so let's return
to the neck region but you would have a similar organization as you have in this image in the
subcutaneous tissue of the anterior lateral neck you will find a muscle which is going to be a
variable thickness depending on individuals which is the platysma muscles so you'll have two one on
the right and one on the left not lining it here this is a very thin flat muscle in fact the name
translates loosely to flat plate this muscle is considered a muscle a facial expression it will
move the skin to convey emotion it we will talk about the majority of these muscles of facial
expression in the face session the platysma muscle develops embryo logically together
with the muscles of facial expression in the second pharyngeal arch so when you have similar
embryological development it makes sense that these muscles are going to share an innervation
or a similar efferent or motor innervation which is going to be from the facial nerve aka cranial
nerve seven so this is our first introduction into the cranial nerves we will be learning about all
12 pairs throughout the course specifically the cervical branch excuse me the cervical branch
is what is going to innervate the platysma muscle so the cervical branch of the facial
nerve the fibers of the platysma muscle will blend with muscle fibers of the other facial
muscles up in this region so you can't see it particularly well in this image it will also
and with fibers of the deltoid which will be in this region and the pectoralis major which is
right here as you can see in this picture the main action of the platysma muscle is to tense
the neck think about your best I don't know face or an individual kind of shaving their
neck region if you think about you know kind of acting that out on yourself you tense up
your neck when you do that so that is going to happen with contraction of the platysma muscle
also went in Singh you can see these vertical skin ridges kind of appearing here in here this
is unless muscle will also play a weak role in depression of the mandible as well as the lower
lip and depression means lowering so think about opening up your mouth you will discover as we
continue to explore the head and neck region that the platysma muscle isn't the only muscle that
plays a role in the depression of the mandible or even the lower lip in fact gravity will play
a dominant role in depression of the mandible keep in mind for the platysma muscle there is a
considerable amount of variability in thickness some individuals may have thicker more robust
platysma muscles whereas for some particularly in older individuals it is difficult to even see the
platysma muscle fibers in the subcutaneous tissue because of how thin the muscle is
alright moving right along let's focus on the deep cervical fascia and it's subdivisions in
the spaces and planes that create I will give you a brief introduction to the divisions today and we
will continue to discuss the fashion and facial planes throughout the course the deep fascia in
the neck specifically is referred to as the deep cervical fascia deep cervical fascia is going to
support the viscera the muscles the vessels those deep lymph nodes that we're going to talk about
of the neck region this fasciae tends to be dense well organized connective tissue with no
adipose tissue so different than the superficial fascia potential spaces between these layers that
we're about to discuss are going to create what we refer to as natural cleavage planes through which
tissues may be separated during surgery without injuring other structures or on the bad side can
actually allow for infection to travel within these spaces usually in a healthy individual
these tissues within these spaces are usually closely adhere to one another or they can be
filled with relatively loose connective tissue there are three main layers and we're going to
talk about them from superficial to deep we'll discuss each one but before we move on I want
you to be aware that if you look at ten different textbooks there will be ten different descriptions
of the fascia so different names different divisions we are going by the terminology
and descriptions in the most up-to-date version of grey's anatomy which is usually quite on the
ball regarding recent research so if you ever look in another textbook you may see different
terms than the ones we're going to discuss here all right we are looking over here and
an illustration of a cross-section of the neck so a section of the body similar to the view you may
see in a CT scan the Investing fascia which you can see in this region all the way around here
you can see it is going to surround the entirety of the neck so you can see it all the way around
here and this nice kind of mauve light color this Investing fascia is the most superficial layer of
the deep cervical fashion and sometimes you will hear this layer referred to as the superficial
layer of deep cervical fascia or my personal favorite the epimysium so in this mauve color
you can see that it's surrounding the entirety of the neck just deep to the superficial fascia and
skin but before we move on what is this muscle right here that is anterior or superficial to
the Investing fashion it is the platysma I'm sure you got it correct remember it is actually
located within this subcutaneous tissue which is superficial to the deep cervical fashion also I
want to note that this investing fashion will send extensions that will actually completely invest
the sternocleidomastoid muscles which you can see here this is also a sternocleidomastoid as well
as the trapezius which is the more posteriorly oriented muscle you can see kind of offshoots of
this fascia surrounding those muscles most sources refer to this intermediate layer
as the pre tracheal layer sometimes you hear it referred to as the middle but think pre tracheal
so anterior to the trachea before the trachea where things often differ our in regards to the
parts and extensions of this layer but before we get into the specifics of the divisions I want to
note that this layer is not nearly as substantial as what we had with the investing layer and it is
only located anteriorly so you will only find the middle layer of deep cervical fascia in the
anterior portion of the neck the divisions of the pre trachea layer are represented in shades
of kind of purplish purplish kind of blueish and as well as let's say sky blue here the
muscular layer and purple is going to surround and you can see this kind of all over the place
here it will surround those infrahyoid or strap muscles that's where it gets its name muscular
whereas the visceral layer you can see here is going to surround viscera such as the thyroid
gland the trachea the esophagus sometimes the buccopharyngeal fascia which I'm underlining right
here is considered part of the visceral layer but either way they are definitely continuous
and you can see that buccopharyngeal fascia in this light blue color behind or posterior to
the pharynx or esophagus you cannot see in this cross-section that it also surrounds the muscles
of the cheek in particular the buccinators so we're gonna call this the pharynx here that's the
majority of what it's going to line and that's where it's getting that for yngeal part of its
name and then the bucco part of its name would be from how it surrounds some of the muscles of
the cheek the pre vertebral layer which you can see in this darker green is closely associated
with the vertebral bodies which is right here and there will be an additional layer of fascia
the alar fascia which I'm underlining right here indicated in light green this is going to be more
anteriorly placed so pre vertebral fascia and then between the buccopharyngeal fascia and the
pre vertebral fascia will be the alar fascia all right so let's talk a little bit about spaces the
space between that buccopharyngeal fascia and the pre vertebral fascia is referred to as the
retromandibular or excuse me the retropharyngeal space were not to the mandible quite yet so the
retropharyngeal space the alar fascia which you can see here in this green is going to further
subdivide the retropharyngeal space into the anteriorly placed true pharyngeal space and the
posterior and frightfully named danger space dr. Fox is going to discuss in more details the spaces
between these layers and their implications of having a space they're clinically but as
I mentioned before these spaces particularly that danger space can be a route for infections
to spread between the pharyngeal region in the neck all the way potentially to the mediastinum
which is a space all the way in the thorax medial to the lungs where the heart hangs out
so that can have some tremendous implications but for this session I just want you to focus
on getting down the look of these fashion layers and the structures that they are associated with
lastly let's discuss this extension of deep cervical fashion that is going to be noticeably
noticeably thicker and this is referred to as the carotid sheath and you can see it outlined
in pink in the illustration I'm circling one of those right here we will be talking quite a bit
about the carotid sheath and its contents and many upcoming videos the sheath will surround
the following structures it will surround the common and the internal carotid arteries with
a little bit of the external carotid artery we typically don't keep that one in there
just because it starts sending out branches the internal jugular vein the vagus nerve or cranial
nerve 10 in deep cervical lymph nodes these are actually fairly large and substantial structures
in the neck so they're going to be wrapped up by a fairly thick layer of deep cervical fascia sources
vary as to what layer of deep fashion that this is an offshoot of but I don't want you to worry
so much about that just understand where it is located alright so that wraps up our discussion
of the skin and fasciae related with the neck but I like to end each of my sessions with a question
that is something like what you may see on your exams to kind of get you thinking in that way
and as a means of review for you if you miss it no big deal just take it as an opportunity
that you to learn that you need to review that area alright so let's do it the question is a
patient is diagnosed with a lesion or some type of injury of the facial nerve or cranial nerve
seven which muscle may be affected is it the platysma is it the sternocleidomastoid or is
it the trapezius take a minute to think it through pause the video if need be but when you are ready
to move on let's hope that you settled on a the platysma muscle yes it is true that this is the
only muscle we discussed in detail in this video but more importantly we know is innervated by
the cervical branch of the facial nerve it is the facial nerve innervation like all other muscles of
facial expression we will discuss in another video but both sternocleidomastoid and the trapezius
muscle are going to be innervated by another cranial nerve so not seven but cranial nerve
11 or the accessory nerve so that completes this session please do always feel free to reach out
to me with any questions after review and thank you for your time and attention have a great day