hi let's talk about intercostal spaces in this video we'll discuss a typical intercostal space
so let's harken back to the osteology of the thorax recall there are 12 thoracic vertebrae
each vertebrae articulates with a pair of costae or ribs so there are 12 pairs of ribs
between these pairs of ribs are intercostal spaces these intercostal spaces are named
for the rib that is superior to them so this is the first
intercostal space this is the second intercostal space and so on and so forth
the inferior margin of each rib is a region known as the costal groove and this is going to be
important for the neurovascular bundle that's going to predominantly serve the intercostal space
and the region where these ribs articulate with vertebrae are known as the costovertebral joints
let's take a look at those so here is a posterior view of a rib there's the head of the rib there's
a neck of the rib and just towards the end there's a tubercle associated with the neck of the rib
now let's look over here at this illustration we can see two thoracic vertebrae there's one and
there's the other this is more of a posterior lateral look at them so anterior is that way
posterior is that way and we can see that the head of the rib is going to articulate between
two bodies and so we'll see that there are these facets that the head of the rib fits in
that tubercle of the rib is going to be received by a facet on the transverse process of the
vertebrae so there are effectively two joints here that comprise the costovertebral joint one for the
head of the rib and one for the tubercle now we think of the bony thorax as something protective
but we also need to consider that it's a dynamic space as well that it's capable of expansion and
then relaxation and one way to conceptualize this is to think of that costo-vertebral joint
as the joint for a bucket hinge and so the handle of this bucket is able to be elevated and then
depressed back down and when that handle is elevated
one might presume that there is more space between the handle and the bucket it's the same with the
thoracic cavity as the ribs are expanded upwards and outwards the thoracic cavity gains more volume
and this is going to be important when we consider how the thoracic cavity affects ventilation
so let's look at the intercostal muscles of which there are three major types all three
of these types are going to affect the motions of the costo vertebral joints hence affecting
whether the ribs are moving upwards and outwards or inwards and downwards so let's look at the most
superficial muscles these are the external intercostals so they were exquisitely well named
the external intercostal muscles have fibers which run medially so if you think of someone putting
their hands in their pockets the directions of their fingers would be commensurate with
the directions of these fibers when they contract they pull the ribs upward and outward much like
elevating the handle of a bucket this increases the volume of the thoracic cavity hence decreasing
pressure hence allowing air to move from atmospheric pressure to reduce pressure within
the lungs these external intercostal muscles are distributed predominantly posterior laterally
there is a portion of these muscles which is connective tissue present anteriorly and we
refer to this as the membranous portion of the external intercostals and this is just fascia
deep to the external intercostal muscles are the internal intercostal muscles the internal
intercostal muscle fibers run inferior laterally so the opposite direction of the external
intercostal muscles let me just draw the external intercostal muscle fibers we can see them running
this way so when the internal intercostal muscles contract they pull the ribs downward
and inward thereby decreasing the volume of the thoracic cavity thereby increasing the pressure
and are more involved with force expiration these internal intercostal muscles are more distributed
anterolaterally and their most posterior portions within the intercostal space are more membranous
deep to the internal intercostal muscles are the neurovascular bundles so the intercostal
nerve artery and vein which serve these muscles and then deep to the neurovascular bundles
will have a group of muscles known as the innermost intercostal muscles
they're not shown here but these fibers run more superior inferiorly
and they will be synergistic to the internal intercostal muscles
meaning they'll help pull the ribs downward and inward to aid with forced exhalation
so here we can see cadaverically some of these muscles so this is a good place to see
the external intercostal muscles and we can even see how this transitions into a more membranous
region more anteriorly and then just deep to the external intercostal muscles so
these intercostal spaces have their external intercostal muscles dissected away
we can see the internal intercostal muscles and their fibers
and then down here surrounded in orange we could see a posterior look at the anterior thoracic wall
so there's the manubrium a couple of clavicles and we can see these innermost intercostal muscles
as well as a type of innermost intercostal muscle known as the transversus the racis if we look over
here we can see a region where those innermost intercostal muscles have been dissected away
and this allows us to see the neurovascular bundles which are serving that intercostal space
keep in mind this is superior this is inferior and predominantly these bundles are going to be along
the superior margin of the intercostal space as we will now see so serving the intercostal space
is a bundle of an intercostal vein artery and nerve as well as a collateral bundle so let's
look at each of these so the vein is draining this space it is most superior in this group
and that's going back to an area known as the aziz system which we'll discuss in a later video
that azages system is the venous system which drains the thoracic wall posteriorly
there's also an intercostal artery which will have two sources that intercostal artery comes
from posterior intercostal arteries from the thoracic aorta and also from
anterior intercostal branches from the internal thoracic artery
we also have an intercostal nerve this is the most inferior within the bundle that's housed by this
costal groove the intercostal nerve is a ventral primary ramus of a thoracic
spinal nerve uh so it's it's the vpr of spinal nerves t1 through t11 and most of t1 is going
with the brachial plexus and a little of it is going out into that intercostal space
now the colla we we can oftentimes remember this arrangement as van vein artery nerve
the collateral bundle are all branches from these and they take the opposite arrangement so there is
a nerve an artery and a vein nav but the vein is always closest
to the rib the collateral bundle tends to be very small and it is not sheltered by a costal groove
so let's take a look at these intercostal arteries and their sources
so all of what we're seeing here is an intercostal artery and the predominant
blood supply are posterior intercostal arteries and these are regular branches
from the thoracic aorta there's also a collateral blood supply coming from the internal thoracic
artery which is a branch of the first part of the subclavian artery as you may recall
and so intercostal arteries have
two forms of blood supply now the first and second intercostal spaces
their posterior intercostal arteries don't come from the thoracic aorta they actually
come from a vessel known as the highest or supreme intercostal artery this is a branch of the costa
cervical trunk coming from the second part of the subclavian artery it's quite variable and it's
typically absent on the left but the remaining spaces 3 through 11 come from the thoracic aorta
in terms of the anterior intercostal branches
the first six intercostal spaces are direct branches from the internal thoracic 8
artery and then the seventh through ninth spaces come from the musculophrenic artery
which is a branch of the internal thoracic artery the internal thoracic artery descends and then
it branches into the superior epigastric artery and then the musculophrenic artery
in terms of intercostal veins
there's a similar situation where there's collateral drainage to the posterior
we have posterior intercostal veins that are draining into
the azygos system and then we have anterior that are draining into the internal thoracic
now again we have segmentation depending on level so the first intercostal space drains into what's
known as the supreme intercostal vein these drain typically directly into the brachiocephalic veins
the second third and fourth intercostal spaces drain into the superior intercostal veins
on the right side the superior intercostal vein drains into the aziz system on the left side
typically directly into the brachiocephalic vein and then the remainder of the spaces
5 through 11 drain into the azigus system which we'll discuss in much further
detail in a subsequent session that azika system drains into the superior vena cava
so we've discussed an intercostal space what it is the various layers of muscle within external
internal and innermost intercostal and the relationship of the neurovascular bundle
as intermediate between internal and innermost intercostal muscles
we've also discussed the relative relationships of the neurovasculature
to ribs themselves and the various branches which are supplying intercostal arteries and veins
this is your summary slide thank you very much for your time