hello anatomy colleagues this is dr alsup and we are continuing our exploration of
the musculoskeletal regional anatomy moving starting superiorly and moving inferiorly
but focusing on the axial skeleton first so that means we have reached the thorax region and we are
going to start with the discussion of the bones and with the bones we'll talk a little bit about
the the joints here we won't have a separate video on the joints just because those costal cartilages
and the connection between certain parts kind of lends itself to this discussion and then of
course we'll finish with the muscles so we will talk about what we mean oops i have muscles here
that should say bones i apologize that was not updated so we're talking bones here and what's
going to make up the thoracic cage and we'll talk a little bit about what we mean by the cage and
then we will talk about the main bones so they'll be the sternum or the breastbone and the ribs
all right so when we say the the word thoracic cage really what we're meaning here is the
skeleton of the thoracic wall and you can kind of see it's going to be these bones
right in this region and it will include um the thoracic vertebrae as well but we we discussed
that when we were talking about the back so we're mainly going to focus on ribs and sternum here
so the thoracic cage is bony when we say the the word thoracic wall this would include the muscles
that extend between the ribs so those intercostal muscles
so as you would uh probably guess or you can think about what you
had previous knowledge regarding the thorax is going to protect organs
and that's one of the main functions of the thorax it's going to protect the primary organs
of respiration so thinking about the lungs the diaphragm will also extend into this area
as well as the cardiovascular system but the inferior portions of the thoracic cage
will also serve to protect some of the abdominal organs some of the more superior abdominal organs
the cage will also uh resist negative or sub atmospheric internal pressures
um this is going to be generated by the elastic recoil of the lungs and that respiratory movement
so there's going to be movement in this area and it will also be an important attachment
site so there will be attachment sites for muscles of the abdomen the neck the back
muscles of respiration but it'll also provide kind of the anchoring attachment site so it's the
origin or the non-moving attachment of many of the muscles that will move or maintain the position of
the upper limbs so the pectoralis major will have attachment here its muscle belly will be located
here but its primary actions will be associated with the shoulder joint so let's start anteriorly
with the sternum sternum means chest we often think of this as the breastbone or the chest plate
and this will directly overlay mediastinal viscera and when we're talking about mediastinal viscera
a much one of the the main things particularly since the sternum is mostly in the midline
it's going to be covering or protecting much of the heart in particular there will be three
parts of the sternum you will have the most superior portion which is the manibrium
or the handle the middle portion will be the body it's the longest portion and the the most
inferior portion will be the xiphoid process and no xiphoid process looks alike there are there's
a considerable amount of variability in the xiphoid process both in terms of size and shape
excuse me my voice is trying to give out on me no no we gotta talk about the sternum
so all three uh all three of these parts they're gonna articulate with one another
and they will be joined uh by synchondrosis so recall synchondrosis are a type of joint
a type of cartilaginous joint many most of these joints will totally calcify but they may not
um particularly between the manibrium and the body sometimes that will not completely calcify
all right a few structures that we want you to be able to identify on the sternum and
the majority of these are associated with the manibrium the first will be the jugular notch
and i want you to kind of put your hand at the bottom or put a finger at the bottom of your neck
and try to find your sternum and one of the first things you'll probably feel is this divot
right here referred to as the jugular notch this will be palpable this is important in terms of
palpating and getting an idea maybe of where you want to inject something or where maybe you want
to put a central line placement because that can help you along the lines of the clavicle
and then just just lateral to the jugular notches you'll have the clavicular notches
these aren't quite as easy to palpate just because you
if you're feeling it on yourself you'll have that clavicle there so this is where the
two clavicles are going to articulate with the manibriums these are the sternoclavicular joints
and lastly right at where the manibrium meets the body is the sternal angle and so if you're
palpating if you found your jugular notch and you continue to move inferiorly you'll feel your
sternum kind of project slightly more anterior than the rest of the sternum and that is the
sternal angle and this is where your second rib it's about at that level that the second rib will
articulate with the sternum so right around this region and that helps in terms of counting ribs
and getting an idea of at what level you are at in case there's any type of injury or just
understanding that also both the jugular notch as well as well as the sternal angle will help
in terms of guiding where a physician wants to put their stethoscope in order to hear specific sounds
all right moving to ribs there will be 12 pairs of ribs or 24 ribs in all
and there are three main categories of ribs ribs one through seven so i'm kind of outlining
these one through seven are referred to as true ribs and the reason that they have this name
is that each one of these will have their own costal cartilage that will articulate with the
sternum all right so they will have its their own costal cartilage connecting to the sternum
many of these will have their articulation with the body of the sternum some with the manibrium
some of the more superior ones so the first of the seventh ribs are considered true ribs
the eighth and ninth and sometimes tenth rib will have an indirect connection to the sternum so what
happens is that the cartilage say associated with uh eight so the costal cartilage here
will not go directly to the sternum because the sternum is too superior for that so what
will happen is it will just attach to the costal cartilage of the seventh rib and sometimes even
into the sixth rib to indirectly articulate with the with the sternum so you can see that
here with the ninth and even with the tenth
so these are referred to as false ribs but they're very very much ribs i think that's
a little misleading of a name but it is all about that indirect connection to the sternum
and lastly the 11th and 12th and sometimes 10th but really you mostly see 11th and 12th are called
floating or free ribs because their cartilages do not connect to the sternums there is cartilage on
the ends of these uh of these ribs but they do not articulate even with the more superior cartilages
so those are the free and floating ribs and they are fairly um nondescript in terms of shape
we'll see we'll see if we will look at another images but you can see that most
of the ribs are kind of curved so they'll have a they'll have their attachment on
the vertebrae which we'll talk about in a moment and then they kind of curve around
there's not as much curvature when you're looking at the 11th and 12th ribs
now in between each of the ribs you will have what's referred to as intercostal spaces
so this will separate the ribs and the costal cartilages and the intercostal spaces are named
according to the rib forming their superior border so the space betw above the first rib
is not an intercostal space but if this is your first rib and this is your second rib
this would be the first intercostal space and kind of so on as you move down all right
this area where you have the the kind of common costal cartilage that's heading towards
the bottom portion or inferior portions of the sternum is referred to as the costal margin or
the costal arch and as costal cartilages are made up of cartilage so will the costal margin
it will also be cartilage and it's really these cartilages that are forming that joint between
the ribs and the sternum so it allows that movement that can occur with the thoracic cage
so we saw a lot of where the ribs articulate with the sternum but the ribs also articulate with
the vertebrae specifically the thoracic vertebrae all right so that is one of the things one of the
reasons why we were able to identify a thoracic vertebrae is because they would have the facets
where the head or the tubercle of the ribs would articulate so the head of a rib
will articulate with the body whereas the tubercle which is pretty close to um but a
little distal to on the rib will the tubercle will articulate with the transverse process
and kind of understanding how those connect for me is always kind of conceptually difficult
so this image i think really shows pretty nicely how you have this region of the rib articulating
with the vertebrae then it will kind of curve around and eventually make its way
anteriorly with its costal cartilages to articulate with the sternum
now each rib is going to look a little different like i said the 11th and 12th ribs or the
um oh excuse me um i will do that later so those 11th and 12th ribs are fairly nondescript they're
not quite as curved whereas the first rib is unique in terms of its shape it is broad it is
short and it is very very sharply curved all right so it has this very distinct curvature um with the
first rib and if you kind of look at some of these other images you can see that it's a little bit on
the smaller side uh oftentimes it's even smaller than that twelfth rib but what is unique about the
first rib other than these things i just mentioned up here is that it's a bit more rugose or robust
in terms of muscle attachments you will have both the anterior and the middle scalene muscles are
attaching to this first rib and those are those muscles that are going to be deeper in the neck so
you actually have that attaching to this first rib so it will look a little bit more robust you'll
have a little a few more bumps associated with the first rib than you'll have in the other areas
okay so question time the clavicle articulates with which part of the sternum is it the body is
it the manibrium or is it the xiphoid process and you kind of look at this picture to help guide you
and so kind of the keys to the stem here are clavicle articulating with sternum
and we know the clavicle is going to be kind of more superiorly placed
so it makes sense i would articulate with the superior most portion of the sternum
which would be the manibrium so b is the correct answer you do have articulations with the body and
the xiphoid in the case of these costal cartilages but it the clavicle this other bone here um
will only articulate with the manibrium and that very you know uppermost or top portion of the
manibrium at those clavicular notches okay so our next video will focus on the intercostal muscles
of the thoracic wall and then we will continue our exploration of the rest of the regional anatomy
thank you for your time and attention here and have a great rest of your day