Foundational features of the brainstem

okay we're gonna talk about brain stem features and answer the what questions what are the three parts of the brain stem and what are the primary internal and external features of the midbrain pons and medulla and their functions hello everyone my name is dr. Morton and I'm the noted anatomist okay so the brainstem consists of three parts it consists of the midbrain the pons and the medulla sometimes known the medulla oblongata so here's a brain stem and anterior view and so this top part here there's the midbrain and just below that is the pons and

then below that is the medulla and so there they are in yellow purple and green and so now let's take a line and separate right down the middle divide them and take one half and protei tit so now we're taking a look at a sagittal section of the brainstem and we can see again the most superior or rostral part is the midbrain in yellow pons and purple and the medulla in green and then below that we can see the spinal cord continuing down through the vertebral canal though you can't see the vertebral canal so this

tutorial is an overview of primary internal and external brainstem features but it's not an exhaustive resource on brainstem anatomy this is main to be a kind of an overview of internal and external features the major ones and their functions so let's talk about midbrain first and so the midbrain is the most rostral part of the brainstem and its rostral to the pons so there in yellow is a midbrain and there's the pons it's superior or rostral to it and so midbrain means middle of the brain mid it's also known as the mesencephalon that embryonic term

because Nissen means middle and Cephalon means brain so the same things and so there we have an embryologist raishin of a developing neural tube and in yellows amis and Cephalon and then if we see the developing tube in an adult that means in Cephalon is in the middle of the brain hence the name so here are all the different internal and external structures in the midbrain that we are going to cover in these succeeding slides so the first is called the tectum and there we have the tectum it's the most posterior region of the midbrain

and you can see in this illustration and the bottom it says brains then posterior view and in yellow is the tectum it's dorsal to the cerebral aqueduct okay so there's the tectum and so if we then take a line and divide it separate it take one half and then twist it so we look at a midsagittal view it's the tectum is this posterior region there is in yellow outlining where the midbrain is and this highlighted part is the tectum it's the most posterior part of the midbrain and then it's dorsal to the cerebral aqueduct so

if we look inside that area there we see that blue line that's showing the cerebral aqueduct and the tectum is dorsal or posterior to that the tectum is Latin which means roof and so it looks like there's the roof of the midbrain just like if we look at a car there's its roof now the tectum also has a component called the quadrigemina plate and quad means four and there's these four swellings on the dorsal part of this midbrain in the tectum one two three and four and so if we take a look at this mid

sagittal view and blow it up we can see a bump so anatomist were like huh there's a bump what do we call this bump hey you know what it looks like a hill yeah like the one that Jack and Jill went up that's a good idea why don't we call it that we'll call it the hill except they're using Latin which is colliculus and so when we now take a look at the quadrigemina plate they call that the colliculus but it's on tops we call it the superior colliculus and then the one in the bottom

they call it the inferior colliculus and so that's singular but if we do plural we use superior colliculi and the bottom fills of the rostral or superior bumps and then the inferior colliculi are the caudal or the inferior bumps so if we then take a cross section through the rostral part of the midbrain through the superior colliculi this is what it looks like where there's the superior colliculi and the superior colliculi function in that they for preliminary visual processing and the conjugate vertical vertical gaze Center and then if we take a look at a cross

section through the inferior colliculi those bottom tube bumps or the inferior colliculi and therefore auditory processing and so here we have a recap we call that whole area there the tectum and then we call those four swellings on the tectum the quadrigemina plate and then we call the two superior bumps the superior colliculi in the inferior bumps or hills the inferior colliculi all right now continuing in this mid sagittal view of the brainstem in purple we see the choroid plexus they're actually located in each of the ventricles and so in this case we concede in

the third and fourth ventricle and the choroid plexus produces cerebral spinal fluid or CSF and so there we have the choroid plexus and the third and the choroid plexus and the fourth ventricles and then we see those arrows are showing now they're producing CSF going in the third and the fourth ventricles and so the cerebral aqueduct courses vertically within the midbrain as shown in that blue vertical line and so the cerebral aqueduct courses vertically and connects the third and the fourth ventricles so there's the third ventricle and there's the fourth ventricle and we see it

connecting the two and there's CSF flowing throughout and so in this mid sagittal view we can see also in this more ghosted lateral view of the brain and there is the cerebral aqueduct coursing up and down connecting third and fourth ventricles so if there's a blockage in the cerebral aqueduct as evidenced by that yellow thing whatever that is as CSF trying to go from the third to the fourth ventricle it's blocked in this results in a non communicating hydrocephalus non communicating because CSF can't get from inside the ventricular system to the through those apertures in

the fourth ventricle to the subarachnoid space okay so there's the cerebral aqueduct so hey how about another name for the same structure so there we haven't in the embryonic term and anatomist were like hey in the embryonic part of this developing brain there's an aqueduct which we call it hey it's in the Me's and Cephalon let's call it the Me's and cephalic aqueduct that a good idea how about another name well why don't we call the aqueduct of sylvius named after the he's German but the Dutch anatomist Francisca Silvius and we'll call it the aqueduct

of sylvius or the Sylvian aqueduct and you know what he looks a lot like Sir Ben Kingsley especially if you do that okay so the cerebral aqueduct in cross-section now through the midbrain is going to look like this and there we have that cerebral aqueduct just like a straw in cross-section and surrounding the cerebral aqueduct is the structure called the periaqueductal gray which is the control center for descending pain modulation and so for now I'm not going to go into any more detail other than that's a landmark to look for that gray matter surrounding the

cerebral aqueduct then there's this other term that we see quite often called the tegmentum so the tegmentum is the region between the cerebral aqueduct and the cerebral peduncles and so there we have it so there's our cerebral aqueduct and there's those cerebral peduncles and it's that yellow shaded area all that area in between there now within that tegmentum is some structures one being the red nucleus so there's a red nucleus and it gets its name because the pink colour red color is due to the iron in the hemoglobin and the Ferren and it's a great

landmark because if you see the red nucleus then you know what you're you're at the level of the superior colliculi because if we then go Shing and go down to the level the inferior colliculi you notice there's no red nucleus all right so the red nucleus it's a it's this rostral location indicates the level of the superior colliculi and it helps in the motor coordination as part of the extrapyramidal system now next is some area called the reticular formation and it forms the central core of the brainstem as evidenced by that kind of orange area

there and the nuclei are not that obvious it kind of makes a formation it looks like reticular just fibers going side to side and the nuclei aren't quite as obvious and so the intermingling of axons gives the formation name and its function as it mediates a level of consciousness alright so next is the substantial that we can see that dark shaded area in this section of the brainstem and it's dark appearance is due to the neural melanin and open Uruk neurons and so of course is from here to here and it's a very good landmark

on identifying midbrain you can see the substantia in cross sections coronal sections or even sagittal sections now if we go down to the level of the inferior colliculus we can also see the substantia though it's consistent all through the rostral caudal levels of the midbrain and the substantia Niagra functions in reward and as a result it also plays a part in addiction and it's also a plays a part in movement in the extrapyramidal system and also in the basal ganglia this also plays a role in and it degenerates in Parkinson's disease so that's Nexus a

structure called the cerebral peduncle it's got this into your lateral location and there's a cerebral peduncle in it courses from up to down or vertically and if we look at this lateral view we can see this whole area in pink is the cerebral peduncle or this posterior view that whole area is the cerebral peduncle and it has axonal fibers that course vertically now what does P Dunkel mean well it's Latin for foot and botany they'd use the word P Dunkel for a short stalk at the base of like a leaf and in anatomy the word

P Dunkel is a stem connecting a massive tissue to another massive tissue in a neuroanatomy P dunkels that bundle of neurons connecting different parts of the brain so all this together means the cerebral peduncle is a stock of nervous tissue that connects the cerebral cortex with the spinal cord brain stem and pons and so the names for the following person have become more or less interchangeable I'm on a bit of a tangent here so you take a look at this person you go oh yeah that person that's Calvin Broadus jr. also known as Snoop Dogg

or just the abbreviated snoop or previously known as Snoop Doggy Dogg and more recently Snoop lion now the names for the following structure have become more or less interchangeable we call this the cerebral peduncle but also now it's become known as the crust cerebri or also the basis peduncle i and so thank you anatomist for making the cerebral peduncle like Snoop Dogg all those names mean the same thing okay so the cerebral peduncle if we now take a cross-section through it looks like this and so that whole area in pink is a cerebral peduncle and

because we've got these descending fibers axonal fibers that go from the cerebrum to the spinal cord and the pons and other parts of the brainstem I'm just gonna focus on one it's called the cortical spinal tract right there okay and so this relays long motor tracts from the cerebrum to the spinal cord but to the contralateral side of the spinal cord now how does that work well let's just show you the schematic we're going to be using here's a cross section through the l4 level of the spinal cord with one side we can see the

roots and rima and then there's a one level with t4 and another through t7 and then there is the medulla and the c1 level the spinal cord showing the decussation and then there's a cross section of the pons a cross section of the midbrain and then there is a coronal section of the cerebral cortex so all of these are cross-sections from brain stem through spinal cord but then in the cerebral cortex is a coronal section alright and there is the right side and there's the left side those are all going to be important as we

use this illustration throughout this tutorial and so three will Pete uncle has the cortical spinal tract that relays long motor tracts to the contralateral side of the body so let's take a look at that picture and go Shi and place it inside this schematic and then we take a look at in a cell body for an upper motor neuron in the right side of cerebral cortex and that axon descends and right there in that kind of rose color we see this axonal fiber and then let's follow it it descends down it decussate sat the pyramids

and then descends all the way down to the contralateral side of the body where it synapses with a lower motor neuron that goes and innervates a lower limb muscle but if we blow this up that's all we see so we now have to superimpose these descending fibers going down at this level and then knowing they're going to go to the opposite side of the spinal cord alright so the next structure we're going to talk about is the spinal thalamic tract or the ALS stands for anterior lateral system and there it is in green and so

the spinal fleming tract relays pain and temperature from the contralateral side of the body and going to the thalamus and so there we have the substantia and if you can find the substantia in the dorsal part of it we're gonna find that spinal fleming tract just medial to it staying along that posterior margin of the midbrain so if we take this section of the midbrain put it in the schematic and go Shing and place it in there and now we're going to take some skin that's in the lower limb on the left side and and

so then take a pin and prick the skin and we see a first-order neuron comes in and then synapse is where the second-order neuron that decussate s' to the contralateral side and watch in the anterolateral system we're part of the spinal cord this fiber ascends all the way up through the different segments of the spinal cord and then bottom part of the brain stem and then Shing right there in green is where this ascending information is relaying pain and temperature from the contralateral side of the body up to the thalamus and then eventually to the

cerebral cortex but all we see is that when we take a look at this cross-section of the midbrain alright so next is something called the dorsal column medial lemniscus or DC ml abbreviation tract and it's there in blue and so the way we this function relays vibration and proprioception from the contralateral side of the body up to the thalamus and so how do we find it well there's a substantial Niagra and then there's the red nucleus and it's right between the two kind of sandwiched between the two is where we find the DC ml tract

it's relaying vibration and proprioception from the contralateral side of the body to the thalamus well let's do this again take this little section and goshi and place it inside the schematic and let's take a tuning fork and hit it on the skin and the lower limb and this on the left side and sew the skin vibrates in this l4 dermatome and a first order neuron brings this information it stays EPSA lateral as it sends all the way up to that spinal medullary junction it synapses with a second order neuron which then decussate to the contralateral

side and ascends all the way up and right there we see in blue this ascending information that's relaying vibrator of vibration and proprioception from the contralateral side of the body up to the thalamus and eventually to the cerebral cortex but when we take a look at these sections all we see is that all right so the cranial nerves coming off the midbrain or oculomotor trochlear cranial nerves 3 & 4 and so there's our oculomotor nerve it exits ventrally from the midbrain and courses out and innervates four of the six extra ocular muscles as well as

the ciliary muscles and the people are constrictor muscle now in the oculomotor nerve exits at courses between two arteries the superior cerebellar and posterior cerebral arteries we zoom in on this there we have in yellow is cranial nerve three and there's the posterior cerebral and there's the superior cerebellar artery and it exits between the two and is important so if there's ever a berry aneurysm that berry aneurysm may compress and then affect negatively that cranial nerve three now cranial nerve four known as the trochlear nerve is shown there now this exits dorsally from the midbrain

it exits door saline wraps around the cerebral peduncle you'll see it's exiting just below that inferior colliculus wraps around the cerebral peduncle and then courses ventrally out and goes and innervates the superior oblique muscle now the functional significance of the midbrain well this is helps its coordination with eye movements it has is one of the real a neurological levels that affects the pupillary light reflex and it also helps with consciousness and arousal through that reticular formation now how do you identify the midbrain in cross-section well some of them you just look for strip things the

landmarks that you've got to know like oh there is the cerebral aqueduct okay I can see that oh hey there's the red nucleus I can recognize that or you could also say oh there's the substantial Niagra it's darker color or there's a cerebral peduncle I see that or you take a look at these two things and say it kind of looks like someone doing the splits there's one way or you might say hey you take a look at that it kind of looks like the years from Mickey Mouse okay so either way you can identify

what the midbrain looks like in cross-section all right now on to the pons okay so the pons is the bulging portion of the brainstem and it's shown there in yellow and it's topography is that it's there and it's basically rostral to the midbrain and it's part of me it's caudal to the midbrain it's rostral to the medulla and it's anterior or ventral to the cerebellum now the topography as I just mentioned there I don't know my own slides okay so in the pons these are the structures that we're the internal and external structures we're going

to cover for the pons anatomy I here's a midsagittal view of the brainstem showing the pons and the pons proper is this anterior bulge as front bulge we see in the pons and if we take this in cross-section and look at it it's here there in yellow is this anterior bulge and we can see these cerebellar tracks that go side to side where we have this bridging action between information going to through the middle cerebral peduncle probably middle cerebellar peduncle going to the cerebellum in the middle of this pons proper in pink is a structure

called the cortical spinal tract there it is there and so there's you're saying that term sounds familiar we're gonna hit this structure at all levels of the brain stem and the cortical spinal tract as we talked about before relays long tracks to the contralateral side of the body alright so if we now take a look at this picture here and put the pawns in we see an upper motor neuron that descends and then stop right there we see this descending or this long motor track on route to the contralateral side of the body well let's

continue it then all the way down it decussate s-- there at the pyramids and then descends all the way down we're on that contralateral side of the body synapses with the lower motor neuron in this case at l4 which innervates some lower limb muscle like your quads okay but if we then blow this up and look at the pons proper in this way and see that cortical spinal tract you now have to superimpose your knowledge on that picture there's another structure called the middle cerebellar peduncle it's just the largest of the three cerebellar peduncle and

it contains fibers that arise from the contralateral pontine nuclei and it courses to the cerebellum there'll be more on that in other tutorials there in blue is the 4th ventricle it contains cerebral spinal fluid and at this fourth ventricle communicates with the third ventricle via the cerebral aqueduct and it continues down into the medulla so there we can see that cerebral aqueduct going up into that midbrain and there's the third ventricle continuation from the cerebral aqueduct and down below you through the medulla and that fourth ventricle that whole continuation in this ventricular system within the

pons errs also the reticular formation and it's located in the pons proper and just in front you know between that and it's located between the pons proper and that fourth ventricle all right now the spinal thalamic or ALS tract there it in green it's a smaller structure no its function is to relay pain and temperature from the contralateral side of the body to the thalamus same one that we talked about in the midbrain and we find it by find the Bulge of the pons proper and then I just kind of go down to the side

like as if I'm going down the slide of a hill and then I find that middle cerebellar peduncle and it's in between that laterally within the pons and so if we take this section of the pons and then superimpose it in the schematic and then we take a pin and prick the l4 dermatome on the left side watch a first Ward comes in synapses with a second-order neuron that that deca states to the contralateral ALS anterolateral system and then that axon ascends all the way up and then right there in the ponds is this information

relay nain and temperature from the contralateral side of the body and it continues up to the thalamus and then ultimately to the cerebral cortex but again all we see is that when we look at a cross-section now the dorsal column medial lemniscus or DC ml track just like we talked about in the midbrain this is going to relay vibration and proprioception from the contralateral side of the body to the thalamus how do I find it well I see the front of the pons proper and just go in to the pons proper and find the cortical

spinal tract and then you just go a little bit more it's between the front and the it's basically right in the middle near the midline in the pons and so if we superimpose this picture and now let's take a tuning fork and hit the l4 dermatome on the left side and a primary order neuron takes that information which ascends EPSA laterally and then synapses with a second order neuron oh that spinal medullary junction in that axon decussate s' to the contralateral side and it sends up to the pons there so right there in the pons

is vibration and proprioception ascending but the information is coming from the contralateral side of the body up to the thalamus and ultimately the cerebral cortex but again when you see a cross-section all we see is that okay so the pons has the following cranial nerves cranial nerves v3 basically 5 6 7 & 8 but it's we're talking about motor and so when we really just talk about the three for the mandibular nerve at this point and so here we zoom in there's the v3 or trigeminal nerve and even though it just says mandibular nerve it's

there's all three branches of the trigeminal nerve but I wanted to focus right there because that's showing the branchial motor component that is going to be going to innervate muscles of mastication then there's the abducens that exits eventually right between the pons and medulla that goes and innervates the lateral rectus and then there's our facial nerve that exits more lateral at that junction between the pons and medulla and that innervates muscles of facial expression and then does visceral motor to your - - of your salivary glands and palatal nasal palate of glands and your Lacan

will gland and also helps with taste from the front of the tongue and then we also have the vestibular cochlear nerve cranial nerve 8 that it looks kind of like a celery stalk that's going to be providing sensory in from innervation of your hearing and balance okay so there are the four principal cranial nerves associated with the pons now the functional significance of the pons is that it's a reflex control of the respiratory system and it it's important in eye movements in the coordinated movements of the eyes and head and it's the neurological level associated

with the corneal reflex you touch the cornea with a wisp of cotton patient will blink both eyes so how can you identify the pons in cross-section we identify these structures like hey there's the fourth fentruck and see that really big it's at the back or oh there's that middle cerebellar peduncle I can see that big big thing coming off the side or oh there's the cortical spinal tract that's right in the middle of the pons proper and also when you just take a look at that pons proper kind of looks like your Uncle Bob's belly

and if you see a cross-section that looks like a big belly you know you're in the pons now let's talk about the medulla also known as the medulla oblongata this is the most caudal portion of the brainstem right there it's below the pons and it's between the pons and the spinal cord and so here are the structures the internal and external structures that we are now going to talk about with regards to the medulla here's an interview of the brainstem and the medulla and then in pink there's the pyramid and it's these paired ventral midline

bulges that course the length of a medulla and if we take a look at it in cross-section it's those pink structures right there that's the internal what the internal what the pyramids look like internally now let's take this contains the cortical spinal tract you're like that sounds familiar because we've already talked about it twice in the midbrain and pons so let's take this section put it right inside there and then we take a look at this upper motor neuron that descends down and right there is where we see this descending fiber right there in the

medulla which decussate s-- through the pyramids to the contralateral side and then descends in the cortical spinal tract in the spinal cord white matter and then it synapses with lower motor neuron which innervate some lower limb muscle like a quad muscle so let's take this section and blow it up a little bit and let's talk about some medulla jargon for a minute it's sometimes this is one of the hardest things you just have a lot of words and it's hard to associate them with the clinical aspects and just the structures in general so that is

showing a cross-section of the medulla and that is showing a cross-section of the c1 spinal cord and the space in between is called the spinal medullary junction spino for spinal cord medullary for the medulla oblongata the spinal medullary junction and then we talk about this upper motor these upper motor neurons and they're called upper motor neurons because they start way up in the cerebral cortex and then they descend and what happens is this upper motor neuron courses in the pyramids of the medulla but then somewhere near the bottom medulla into the spinal medullary Junction this

decussation occurs the decussation means a crossing over so this cortical spinal tract are these upper motor neurons of course down the pyramid decussate in the spina medullary junction and then descend in continuing this tract the tract of upper motor neurons that go from the cerebral cortex to the contralateral spinal cord called the corticospinal tract I'm hoping that might be helpful and taking all these terms and trying to understand them alright some other structures in the medulla is called the Olive there in yellow these paired in tier lateral bulges that are just lateral to the pyramids

and let's take a cross-section and see what this looks like these paired anterior lateral bulges contain the inferior Oliveri nucleus very very characteristic of the module if you ever see that that squiggly dentate looking nucleus you know aha there we've got I sound like a pirate there know where that came from there we got a cross-section through the medulla more on that on this functions but right now it's basically so you can identify one of the features that identifies the medulla at the back of the medulla is this fourth ventricle which contains cerebral spinal fluid

and the fourth ventricle is where the CSF communicates with the subarachnoid space via the medial and lateral apertures of Magendie and Luca okay now in orange there is the reticular formation which you've noticed we talked about in midbrain and pons and I medulla which plays a key role in cardiovascular and respiratory systems all right in green is the spinal thalamic tract or the ALS tract and this is relaying pain and temperature from the contralateral side of the body to the thalamus you're like hey this sounds familiar this is like a broken record but it's always

repetition I'm hoping is helpful so how do we find that in this cross-section the spinal cord I use friendly faces I take a look and say pyramids I can identify that oh and just lateral to that is the UM in fear Oliveri nucleus so I know it's that so if I just keep laterally on the periphery right behind that is where you're gonna find the spinal phlegm attractor okay and so if we now take that section and place it in the schematic and then we take a pin in pricks skin and the left side of

the l4 dermatome we're gonna see that information comes around and ascends and then right there again is pain and temperature coming from the contralateral side of the body ascending going to the thalamus and then watch it goes through that part of the pons and midbrain thalamus up to the cerebral cortex okay so there we have the spinal Fleming tract in the medulla now the dorsal column medial lemniscus tract is a relaying vibration and proprioception from the contralateral side of the body to the thalamus and so they're how I find as I find the the pyramid

and then this DC ml tract is just immediately dorsal to the pyramids and it spreads a good chunk I and through the mid portion of the medulla and so if we now in place that within our schematic there we have a tuning fork that hits the skin in the l4 left side of the l4 dermatome that information ascends itzá laterally synapses with a second order neuron that decussate s' to the contralateral side and ascends up there so there in that part of the medulla is vibration and proprioception ascending to the thalamus but it's taking information

from the contralateral side of the body up to the thalamus and ultimately cerebral cortex and there we have the DC ml tract DC ml tract in the medulla in fact right here it's really just called the medial lemniscus because it looks kind of like a ribbon the way it ascends up through the brainstem and the dorsal column is for the spinal cord but for the whole tract we just call it the DC ml tract alright know the cranial nerves associated medulla or cranial nerves 9 10 11 and 12 and so there's the glossopharyngeal nerve cranial

nerve nine that innervates stylopharyngeus muscle clinically not so significant does the taste of the posterior third of the tongue and oral pharynx kind of general sensory to the posterior third of the tongue and oral pharynx so it's important for the gag reflex and then it also innovates the parotid gland then there's our vagus nerve that is cranial nerve number 10 and that's the Vagabond that's the one that goes and provides parasympathetic innervation to the heart lungs and foregut mid gut and associated organs but it also does branchial motor to your palatal fringy and laryngeal muscles

which is very important especially for swallowing and speaking and then there's our spinal accessory nerve that ascent that kind of arises from the more rostral part of the cervical spinal cord at a sin's up through the frame and magnum and then descends through the jugular foramen with cranial nerves 9:10 on route to innervate the traps and sternocleidomastoid and then there's our hypoglossal nerve cranial nerve number 12 that innervates all the tongues of the muscles of the tongue helps you move your tongue out of your mouth and it exits the medulla between the all of in

pyramids very easy to find on a brain all right so there are our four cranial nerves associated with medulla now what is the functional significance of the medulla oblongata well it has a reflex control of cardiovascular and respiratory systems and also reflex control of swallowing and vomiting and it's important information phonation control of the tongue and movement of the laryngeal muscles and fringe' muscles now how do you identify the medulla in cross-section well you can see Hey look there's a fourth ventricle I can recognize that or oh there's the pyramid I can recognize that near

the midline oh there is that cool inferior ovary nucleus I can definitely tell that or you take a look and say you know what that looks like that looks like a plumber's crack if you ever take a look at a cross-section in the brainstem and it looks like a plumber's crack you're in the medulla and so let's now in review talk about the brainstem in a nutshell so here we have an interview the brainstem and it's um comprised of the midbrain pons and medulla and in cross-section the midbrain looks like this and there's all the

structures associated internally and externally and the pons there's a cross-section and there's all the structures that are internal and external in the pons and there's a cross-section in medulla and all the structures that you need to know for internal and external and they're my friends is the brainstem in a nutshell [Music]