so when we talk about the brainstem and we talk about very specific levels of the brainstem and
we talked about the cranial nerve nuclei way back in the beginning of this series when we
were discussing the gross anatomy of the nervous system we talked a little bit about gray matter
and white matter grey matter neuronal cell bodies and proximal dendrites white matter
myelinated axons that are bundled together to form tracts and some tracks are then bundled
together to form funiculi and so on now in the cortex and in the spinal cord these delineations
between gray matter and white matter are pretty cut-and-dried and they're pretty oh they're just
pretty regulated and normal are pretty standard looking is what I'm trying to say and you can
see in our cartoons that in the spinal cord the gray matter is on the inside the white matter
is on the outside and when we're talking about our cortex our gray matters on the outside and
our white matters on the inside in the brainstem things get a little less clear in that you can see
all kinds of areas so here's some white matter these I want to draw your attention to the fact
that these three sections are stained with a myelin stain so the myelin looks dark and the
grey matter looks light so it's kind of flipped but the bottom line is here's a bunch of fibers
here is some cell bodies here's a whole bunch of cell bodies around the cerebral aqueduct here's
a great big bundle of fibers and then you can see that oh there's some cell bodies there's some cell
bodies there's cell bodies all over the place in here with fibers interspersed and so what the heck
is going on well the brainstem is a transitional area between this gray on the inside white on the
outside and the white on the inside and gray on the outside so that's part of what's going on and
we have within the grade within the brainstem we have very specific nuclei for very specific
cranial nerves those are all named and theirs are for the most part pretty easy to find but there's
something else that lives in the gray matter within the brainstem that's really important and
that I really want to tell you about and that's the reticular formation the reticular formation is
a very diffuse group of neurons that lives within the medulla oblongata and the pons there they're
not formed into any specific clusters they're kind of loose aggregations of cells within the medulla
and the pons they receive sensory information both somatic so from your surface and visceral
from your internal organs they don't receive real specific information like they don't receive Oh
a mosquito bit me or Oh a q-tip ran across my arm or or oh this part of my my stomach hurts
but they have kind of a general awareness that something's going on but not real specific the
reticular formation then sends that information up through the brainstem into the diencephalon
which remember is continuous with the brainstem and then on up into the cortex so it goes through
your thalamus which is a sensory gateway it goes through the hypothalamus which we'll talk about
later and it has a lot of regulatory functions and then on up to your cortex there are also
then descending projections of that reticular formation down your spinal cord okay and this
is going to interact with the lateral and ventral corticospinal tracts and all of the other neurons
that are impacting on the ventral horns to kind of have an effect on your muscles so it's the
reticular formation it's it's kind of a general awareness thing an awareness of motion and an
awareness of sensation that is very important for just kind of a general state of arousal and
I don't mean arousal in any sort of romantic kind of way I mean arousal in the sense that you're
awake okay so noise bright light vibration those things can wake you up out of asleep because your
reticular formation is getting those sensations from the periphery and then reliving them up
to your cortex without you even being aware of what woke you okay that's the gist of it not the
specifics that's just kind of the general gist there are also some really important things in
the reticular formation that have to do with your heart rate and your respiratory rate so centers
within the reticular formation are setting the tone for breathing and heartbeat which is one
of the reasons why if you have damage to your brainstem via injury or stroke it can kill you
because the neurons talking to your heart and talking to your lungs would no longer
be working and you would cease to breathe and your heart would cease to be beat the reticular
activating system is also part of this particular formation and it is what then is responsible for
you being not in a coma so if when you hear about people having brain stem damage and then being in
a vegetative state it's because the reticular activating system is not sending information up
through the thalamus and up to the cortex for you to be awake and you do end up in what is called a
coma or a vegetative state so in summary what do I want you to know about the brainstem so what are
the different regions which is the most cranial which is the most caudal be able to describe the
most prominent surface features of each area think about the olive think about the tectum those kinds
of things what radial nerves are associated with each area of the brainstem okay what are
in the medulla which cranial nerves are in the ponds which cranial nerves are in the midbrain
and what are some of those internal features that I talked about think about decussations
think about the fourth ventricle think about the cerebral aqueduct and then lastly what I want
you to think about is what is the reticular formation where is it and why is it really
really really important if you understand all of these concepts then you're ready the assessment