hello anatomy friends this is dr alsup and in this supplementary dissection video we are
going to be talking about some of the structures that will actually be visible associated with the
spinal cord and the spinal nerves so we will start with the spinal cord and um this is a
very obviously close-up version of this picture here i put this picture here because it is um
pretty clear that you're looking at the large vertebral body and real quickly
think about the vertebral body in terms of its directionality is it located anterior or posterior
it's going to be located more anterior or more ventral so that helps in terms of being able to
determine which horns of the gray matter you are looking at so that always helps me when i
am trying to get my bearings in terms of the gray matter so this gray matter which is this kind of
butterfly shape region in the inner portion of or the more internal portions of the spinal cord
are they're going to be organized into horns so the ventral or anterior horns are going to
be the horns that are closer to the body and you can see those right here another
thing that is that can be helpful in terms of identifying the ventral horns is that they're
typically on the larger side they're going to typically be larger than the dorsal horns
recall that the ventral horns are going to be only motor as well and the the dorsal horns will be
only sensory so ventral is going to be motor dorsal will be sensory now in certain areas you
can see a little bit of a lateral extension right here and these will be called the lateral horns
still part of the gray matter right here um their actual name is really interomedia lateral nucleus
or the iml but we are going to um you you'll very often hear them referred to
as lateral horns and these are going to be most obvious at the t1 through l2 spinal cord levels
and that's because they are associated with the sympathetic division of the autonomic nervous
system and you'll also have these lateral horns associated with levels s2 through s4 and those
will be associated with the parasympathetic division or of the autonomic nervous system
so more to come in terms of the autonomic nervous systems but while we're looking at the spinal cord
at least we can get an idea of where the lateral horns are and then surrounding a more external
will be the white matter so this whole region around here would be part of the white matter
all right moving to the spinal nerve um the much of the lateral vertebrae had to be removed in
this image in order for us to really be able to follow the full extent of the spinal nerve
when you are dissecting through a laminectomy procedure so you're
looking in from a posterior view it's easiest to see the dorsal portions of the spinal nerve
and that makes sense we're looking at a posterior view but we can see some of the anterior ventral
portions of the spinal nerve in in this particular image so you will have the dorsal rootlets
that will coalesce into a dorsal root and you can see a bit of the ventral root right here
and it will kind of continue on this region associated with the
dorsal root is this often very quite large or comparatively large dorsal root ganglion
and it's here that cell bodies for sensory neurons will be located so recall a ganglion
when we're talking about the peripheral nervous system is going to be collection of cell bodies
the trunk of a spinal nerve is going to be this relatively small portion
right here where the two roots are going to meet so both the dorsal and the ventral roots will meet
to form this trunk of a spinal nerve and at this point this is going to be a mixed nerve at this
point so you'll have both those sensory and motor fibers traveling in the trunk of the spinal nerve
and very often times you don't hear this referred to as the trunk of the spinal
nerve you'll just hear this referred to as the spinal nerve really this whole complex is part of
the spinal nerve almost immediately the trunk will split into the primary rami
which are the first branches of the spinal nerve so you will have the dorsal primary
primary i'll put a p here so dorsal primary ramus and the ventral primary
ramus again you can see that dorsal a little bit better in this posterior view and you can
see with this dorsal primary ramus that it's going to start splitting fairly quickly so that dorsal
primary ramus as well as the ventral primary ramus will almost always have numerous numerous branches
many of those branches will be named branches that we'll discuss throughout the course
okay we're looking again at the uh the laminectomy that has been completed the dura mater has been
removed in this image and we are looking at the entirety of the spinal cord all the way
down to even the end of the spinal cord here which we'll talk about in a moment
there are going to be what's referred to as enlargements associated with the spinal cord
and these happen in regions where there are an increased number of lower motor neurons
and this will be associated with what's going to innervate the appendages so you'll have a cervical
enlargement which you can see really nicely right here that's associated with c4 through t1
and this is going to play a role in terms of innervating the upper limb
but the one that you have to identify for today's session will be the lumbosacral which is going to
be in this region it will be associated with um the the t1 excuse me through or sorry t11
through s1 portions give or take and this will be associated with innervating the lower limb so you
can see that it's just basically that spinal nerve just gets a little bit wider in these regions
and then it kind of gets back to its normal size with the with the kind of middle thoracic region
all right let's talk about the end of the spinal cord so you can see here a lot of
that vasculature associated with the spinal cord but you can kind of pick up where the spinal cord
is located right here and then you can see eventually it kind of lowering and tapering
till eventually it ends and this area this end of the spinal cord the inferior end of
the spinal cord is the conus medullaris so this region right here would be the conus medullaris
it's typically between t12 through l3 but usually you'll hear us say it is at l2 so that tip of the
conus medullaris or the very end of that spinal cord will be around l2 and extending from the
spinal cord and then um traveling or descending to its targets to eventually exit will be what's
referred to as the kata aquina so it's this whole all of this right in this region on both sides
and the cauda equina is named um because it supposedly resembles a horse's tail
and the caudaquan is the roots of the spinal nerves and for the lumbar and sacral regions
so very different appearance to these roots than say what we saw in those more superior portions
in that previous image all right excellent that was a lot of spinal nerve and spinal cord fun
as you review this and if you're having some questions about
uh identification or an anatomical relationship associated with these structures always feel
free to reach out to me or any of my colleagues i'm hoping you are having
a good time working through this material and i hope you have a good rest of your day