hello all this is dr alsup and in this learning objective video we will be exploring the meninges
with an emphasis on the spinal meninges so the primary focus will be of course on the
meninges but there are a few meningeal specializations that we want to touch on
in addition to the spaces these meninges will create
and so there are three membranous layers called meninges that surround the central
nervous system which include the brain and the spinal cord and from most superficial to deep
we start with the dura mater which is the most robust it literally means tough mother
there are two layers of the dura around the brain so you can see it here and here but there is only
one dural layer associated with the spinal cord so kind of around the edge right here
the arachnoid mater is intermediate and closely adhered to the dura mater and um you can see that
kind of right in this region here and it's separated from the pia mater by these spider-like
projections called arachnoid trabeculae and this is where arachnoid mater gets its name because
these are supposedly very spider web-like and deepest and very intimately related to either
the brain or the spinal cord and kind of extending into the the rootlets and the extensions from the
spinal cord you will get the pia mater and this is a very delicate transparent covering
the dura has two major specializations in the spinal region that i want to discuss
the first is the dural sac which actually extends from the margin of the foramen magnum
all the way to approximately c2 or the second sacral vertebral level which is actually well
past where the spinal cord actually ends and it ends at about the spinal cord entered about l2
at this area called the conus medullaris but the dura still needs to surround the kata aquana
or these lumbar and sacral nerve roots that are going to extend from the end of the spinal cord
and so this whole area right here all of this is considered part of the cauda equina
it's supposedly resembles a horse's tail so that's where it gets its name and it's in this region
between the conus medullaris but still within the dural sac that a lumbar puncture typically
occurs and so the needle will enter this region and it will allow avoidance of the spinal cord
because if you go below the spinal cord and that needle will kind of cause those roots to move away
allowing extraction of csf if you get passed into the subarachnoid space for diagnostic purposes
such as in suspected meningitis so typically the needle is entered between the spinous process
processes of between l3 and l4 or l4 and l5 and what we call the super crystal plane and we'll
talk a little bit more about this in another video but kind of that highest level of the
iliac crests so if you put your hands on your hips your hands are resting on the iliac crests
and you kind of follow that back to the vertebral column and it's about in that area where you would
want to enter the needle between the spinous processes in order to enter uh towards this
space so you want to be between that spot the end of the spinal cord but still within the dural sac
another dura mater specialization is the filum terminale externum often referred to as the
coccygeal ligament because it is extending all the way to the coccyx so it's visible from the end of
the dural sac to the coccyx it's typically quite small and it will envelop the phylum
terminale internum which is actually a pia mater specialization that will begin at the end tip
of the spinal cord at the end of the conus medullaris and travel within the dural sac
and this whole filum terminale uh complex is going to play an anchoring role for the
spinal cord and meninges and here is that filum terminale internum that we were just discussing
and it's usually distinguishable from the uh from the cauda equina that's surrounding cauda
aquina here um as being kind of more noticeably white and so i'm kind of drawing a line next to
where this is it's kind of usually right equina the midline region and so kind of in
the middle of the cauda equina and usually it's a little it's wider than the surrounding roots
and as we mentioned the internum will be enveloped by the
externum or the filum terminology externum at the level of the end of the dural sac
the last pia specialization i want to discuss are these super cool denticulate ligaments which
will be extensions of the pia mater from the lateral portions of the spinal cord to attach
to the arachnoid lined dura or dural sac and these will be collocated
between the dorsal and ventral rootlets and roots of the spinal nerve
there aren't denticulate ligaments at every spinal cord level as you can see here they're only 20 to
22 with some variation there but similar to the phylum terminale this will play an anchoring
role of the spinal cord in this area so you can see a little bit here a little bit here
and you can see what they actually kind of look like in a cadaveric dissection over here
all right now let's talk spaces real and actual spaces and what in the heck do i mean by that
well a real space is naturally occurring and it's often observable so this is what you should see in
typical anatomy a potential space means that it is not net it's not a naturally occurring space as in
the space does not typically occur unless say an infection enters the area or blood enters between
two layers or air so the typically non-existing space between a layer becomes an actual space
so let's start with the most superficial space and this is the epidural space
this is going to be located between bone and the dura mater but depending on where we're talking
um what type of bone will differ and the cranial region the periosteal dura
is very closely adhered to the bone and so this is actually a potential space and let's say in
a case of an epidural epidural hematoma where blood can enter into the region creating a space
so this is a potential space in the cranial region but it's an actual space
or a real space in the spinal region so between the dura and the spinal dura mater this space will
actually be filled with epidural fat and lots of venous plexuses and very typical anatomy so
this is an actual space in the spinal region the subdural space is a potential space in both the
cranial and spinal regions and it's going to be located between the dura and the arachnoid mater
this is a ver and that dura and arachnoid matter are moderate are very typically closely adhered to
one another so again this is a potential space you can kind of see where this would be located here
and last but certainly not least is one of the best the subarachnoid space which is an
awesome space because this is where cerebrospinal fluid or csf will flow so you'll very often see
a cerebrospinal fluid fluid abbreviated as csf and csf will surround and protect the cns
it's very important something that you want to have flowing appropriately and not lost this
space the separate noise space is located between the arachnoid and pia mater so sub the arachnoid
and not only is it filled with csf but it can is also filled with vasculature particularly
in the cranial region neurovasculature in fact and of course those arachnoid trabeculae which
you can't really see very well here but that's what gave um that kind of spider-like appearance
betw within the subarachnoid space so that is it for the meninges that was a
lot of fun and of course i always like to end with the super awesome summary slide
always please feel free to reach out with any questions and have a great rest of your day