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