Neurology | Midbrain Anatomy & Function

all right ninja nerds in this video we're going to talk about the mid brain so let's go and get started all right guys so let's go ahead and get started about talking about the midbrain so what we're going to be doing in this video is we're going to talk about the midbrain right we're going to look primarily at cross sections or transverse sections and i'll explain a little bit more about that in a second of the midbrain but we're going to look at it at two levels okay one is going to be the one over here on the left and that's going to be at the level of the inferior colliculus right the other cross section is going to be the one here on the right that we'll look at in a little bit and that's going to be the level of the superior colliculus let me explain that just a little bit so we have an idea of orientation i'm going to draw a sagittal section here right so here we're going to have the obviously the cerebrum our midbrain right so bring our midbrain down we got our pons we got our medulla and then we have a part of the spinal cord right and if you guys want for like simplicity stake we got here the cerebellum right well if you guys remember here this is going to be the anterior portion this portion here is going to be the anterior portion right of the midbrain and then back here is going to be the posterior portion of the midbrain or the dorsal so you can say ventral portion or anterior portion posterior dorsal portion of the midbrain on the dorsal portion you're going to have like these little knobbies that are just hanging out in the back here okay these are called your colliculi right so you'll have the one above here which is your superior colliculus and then the one below which is your inferior colliculus right so what we're going to be doing is we're going to be taking cross sections and we're going to take a cross section here at the inferior colliculus look at all the internal structures and then we're going to take a cross section here at the superior colliculus and that's going to be on the right here and look at all the internal structures and then after we're done with that we'll talk about some of the relative function of a lot of these internal structures okay let's go and get started on that all right so now we're looking at that cross section like we said right so this is the cross section at what level the inferior colliculus right inferior colliculus we're going to talk about all the structures and we're going to kind of annotate them right first what are their names okay and kind of their overall like anatomical uh positioning and then after we kind of get that down then we'll go through some other diagrams to give you guys different views on their function so first thing this portion here this green portion this green portion here this is going to be on the ventral portion of the membrane to give you guys some anatomical orientation back here these two bumps in the back that's your inferior colliculi that's going to be that dorsal portion of the midbrain okay so ventral dorsal on the ventral portion here we have some very important structures that i need you guys to remember here these guys here okay this whole component here in this anterior portion i'm going to kind of make it like this see this thing right there that whole chunk there of this green portion is called the cross cerebri if i were to give you kind of just one sentence kind of one simple thing of what the function of this is this is where the descending pathways are moving what's descending descending pathways are motor pathways so they're for motor movement right so muscle activity now there's three subdivisions within this crust cerebri that we have to know the most medial portion here right so the most medial portion this is consisting of what's called the corticopontine fibers remember that's coming from the cortex down to the pons but you know what part of the cortex is actually coming from the frontal lobe so we call these frontal pontine fibers frontal pontine fibers this medial portion now let's go to the the middle portion the middle portion is very important this is where the corticospinal fibers are moving through and one more corticonuclear so two fibers here cortico spinal and cortico nuclear fibers are running through this middle portion okay corticospinal simplistic way neurons from the cortex going down to the lower motor neurons in the spinal cord to go out to the muscles corticonuclear or corticobulbar is neurons in the cortex going down to the cranial nerve nuclei such as three four six so on and so forth okay so corticonuclear corticospinal is in this middle portion here the most outer or lateral portion of these crust cerebri here is going to be made up of other cortico-pontine fibers but these cortical pontine fibers are not coming from the frontal lobe they're coming from almost all the other ones so what are the other ones the temporal what else parietal what else occipital pontine fibers okay so again you have the temporal parietal occipital and pontine fibers really quick point simplest way i can make it very important clinically the corticospinal corticonuclear fibers the reason why i'm kind of emphasizing so much on this is if you guys remember you can have like a little homunculus like a little man and it kind of gives areas of the body that a certain pathway might supply based upon the region of the body i want you to remember at the most medial portion here the most medial portion of these kind of corticospinal corticonuclear fibers this is going to supply more of the head even a little bit of the front toe pontine fibers do that as you go more laterally through this middle chunk you're going to start supplying the trunk as you get down towards like the outer portion of this corticospinal and the corticonuclear pathway it'll start going more to the lower extremities okay so here's what i want you to remember this little homunculus little stick figure that i'm drawing here this kind of gives us relatively the fibers that are in this middle the medial portion of this middle chunk supplies more of the upper body the middle might support more of the trunk and then this lateral portion or outer portion of that middle chunk might supply the lower extremities so if there is a lesion for example involving only this portion here it might only involve the muscles of the head if it's involving this portion it might involve the muscles of the trunk if it's involving this portion it might involve muscles of the lower extremities that's the importance and significance i want you guys to take home all right good we got the ventral portion of the midbrain the next portion we have to talk about is we're going to cover all of this stuff between the inferior colliculus and the crust cerebri you know what that's called this whole chunk here from this point all the way forward from here all the way to this point here is called the tegmentum it's called the teg mentum and there is a bunch of stuff in the tegmentum so much stuff in the tegmentum what are some of the things that we're going to talk about okay let's first move on to this structure you see this structure almost everybody in science knows this structure this is the substantia substantia everybody knows that this is what's basically damaged it leads to parkinson's disease right well there's two components of the substantia this dark component this dark component is called the pars compacta okay so the pars compacta pars compact is the dark dopaminergic producing neurons can't stress that enough this is the ones that produce dopamine this lighter colored one this guy is called the pars reticularis and the pars reticularis is the gabergic producing neurons they release gaba gamma-aminobutric acid combined both of the pars compacta and the pars reticularis make up the substantia okay all right so the next thing we have to do is cover some of these ascending pathways right so the ascending pathways are the sensory pathways right they're carrying fine touch discriminative touch pressure proprioception pain temperature all of that stuff and even auditory sensations they're all being carried through these purple fibers here okay so we're going to cover them each individually starting from medial and kind of working our way laterally and then dorsally right so first one here just behind the substantia this guy is called the medial liminiscus now a lot of you guys if you guys have watched a lot of our videos in the neurology playlist we've already talked about the dorsal column medial meniscus pathway we'll briefly go over that a little bit later but this is a sensory pathway right for proprioception fine and discriminative touch okay and even vibratory sensations the next one as we go a little bit more dorsally right is the trigeminal lumeniscus so this is the tri geminal lemoniscus now the trigeminal lemoniscus is important because this one is taking sensations from the face right so more of proprioceptive sensations touch sensations pressure sensations these are going to be a part of that part of this ascending system go a little bit more back this is the spinal meniscus the spinal limb meniscus is important because this one is carrying uh ascending fibers from that pain and temperature and even crude touch and pressure sensations from your anterior and lateral spinal thalamic tract and even a little bit from the spinal tectal pathway so again medial meniscus trigeminal meniscus spinal luminiscus and the most outer one or lateral portion here is the lateral lemoniscus so many luminous guys right so lateral luminiscus simple way one sentence kind of thing is it's involved with your auditory pathway so from the vestibulocochlear nerve the cochlear part though okay all right so the next thing that we got to talk about here is let's go into the middle portion of the tegmentum so we've already kind of covered some of the outer portions let's go into the middle and then kind of like work our way through all of these structures big couple structures here okay you see this guy here this pink nuclei here okay they're actually kind of around the periaqueductal gray matter and kind of a part of it but to kind of keep it separate make it more simplified we've got these pink nuclei that are a part of that periaqueductal gray matter you know what this guy is called it is called the we're going to have kind of these little key out here so we don't get our diagram all crazy but it's called the locus ceruleus locus cyrillius you guys know this locus cerulus is where most of the nor adrenergic neurons are produced so they're responsible for releasing large amounts of noroepinephrine remember this when we talked about the descending pain pathway this is involved within the descending pain modulation pathway right so they basically release norepinephrine that inhibits some specific pain pathways we'll talk about a little bit later but if you guys haven't already you guys can watch our video on that we have a video on the descending pain pathway all right go a little bit more anterior a little bit more anterior we have another group of neurons that are also involved in the descending pain pathway you see these green guys here we're going to kind of look at them right here this is called the dorsal raphe nucleus so the dorsal raphe nucleus so again i want you guys to remember both the locus cyrillius and the dorsal raphe nucleus are involved in the descending pain pathway sweet deal let's move a little bit more ventral you see these guys here these maroon colored guys these maroon colored guys here is the mesencephalic nucleus of the trigeminal nerve right so this is the mesen cephalic nucleus of cranial nerve five your trigeminal nerve you guys remember the trigeminal nucleus it extends all the way from the midbrain all the way down to the medulla well this is the portion of the trigeminal nucleus that is in the midbrain there's going to be one of the pons there's going to be one in the medulla again this guy picks up some of that proprioceptive information right from the trigeminal nerve so the proprioceptive information is the basically the position sense of our muscles and our tendons and our joints from those mastication muscles and basically sends it to these nuclei which relay that up through the trigeminal meniscus right so you see kind of the connection there all right next one we go and cover some of this structure here so we have this central structure here there's this little tube a little tube here with some actual fluid in it right that little tube with the fluid in it the cerebral spinal fluid is called the cerebral aqueduct so again we're going to kind of bring it out here so the little tube with the blue stuff in it is called the cerebral aqueduct now if you guys remember the cerebral aqueduct is the little tube that connects what above it is the third ventricle below it is the fourth ventricle so it's connecting the two fluid-filled spaces in the central nervous system which again superior is the third ventricle inferior is the fourth ventricle so cerebral aqueduct now all of this kind of like gray matter surrounding it is called the periaqueductal peri aqueductal gray matter i want you to remember that so all of this kind of stuff surrounding the super aqua duct is called the periaqueductal gray matter so we have the cerebral aqueduct and around it as the periaqueductal grain matter sweet let's move on to the next thing so now we have these next group of fibers here this next group of fibers here are located within just anterior to this periconductor gray matter and this is called the medial longitudinal fasciculus so again here we have these blue dots here this is called the medial longitudinal fasciculus you guys know this we talked about this with the vestibulocochlear nerve this is basically connecting the vestibular nuclei which is in that pons medulla junction to what three cranial nerve nuclei three four and six it's basically responsible for helping to accommodate proper eye movements based upon vestibular sensations right like whenever we're rotating our head to the left or rotating our head to the right okay so again medial longitudinal fasciculus is a ascending kind of pathway white fibers white matter right that are connecting the third fourth and sixth cranial nerve nuclei together all right move a little bit more anterior we have these blue fibers okay and again a lot of this is all ascending fibers these blue fibers here are going to be a part of your tacto spinal fibers so again this is going to be the tecto spinal fibers and we will get into a little bit more detail on what the heck the tectum is in just a second all right simplistically one sentence kind of thing tacto spinal fibers are basically taking information from your tectum and we'll talk about in a second what that is and it's taking that down and sending that information to your spinal cord to control muscle movement what kind of muscles primarily muscles of the eyes and muscles of the neck the whole purpose here is what i want you to remember is that the tectum is going to be made up of two structures here the superior colliculus and the inferior colliculus simplistic way to remember superior colliculus receives visual input okay inferior colliculus receives auditory input so whenever we're following or tracking something what are we doing if i'm following somebody moving i'm moving my head and my eyes in that direction who does that super colliculus if i hear someone yelling my name and i look towards that i fix my gaze and i move my head towards that direction who's responsible for that the inferior colliculus and guess who controls that the tectospinal fibers okay all right next one these red fibers here these red fibers are again these are descending fibers and this is via the rubra spinal pathway so the rubro spinal pathway these are going to be taking fibers from the red nucleus going down to the lower motor neurons and controlling motor movement primarily of the flexor muscles and the distal extremities so we have here the rubro spinal fibers or the tract right so the rubra spinal tract okay sweet again rubra spinal red nucleus we'll talk about that in a second that's at the level of the superior colliculus it's going to send descending fibers that are going to go to flexor muscles one more structure to cover here that covers the tegmentum and this is this little kind of like lattice crossing structure here all the way in the ventral portion this right here is called the decussation of the superior cerebellar peduncles that is one heck of a thinner site right so we have here in the front this little lattice-like structure here we have the decussation of the superior cerebellar peduncles all right sweet deal now what the heck do these things do simplest thing i want you to remember again we'll go into a little bit more detail of it later this is going to be consisting of fibers coming from the cerebellum moving through the superior cerebellar peduncles and they're going to go to two structures one is they're going to go to the red nucleus which is a level above right the superior calculus and then from the red nucleus it can go up to the thalamus which is in the diencephalon so these fibers are connecting the cerebellum to the red nucleus or cerebellum to the thalamus and eventually what that's going to lead to is it's going to send fibers up to the cortex because remember what's the cerebellum doing it's involved in kind of helping us unconsciously to play a role within coordination posture tone of the muscles all of that stuff so it sends up a motor plan to the cerebral cortex with the exact calculated way that we should move so a deca station of the superior cerebellar peduncles is going to be fibers ascending fibers that are coming from the cerebellum contralateral so they're crossing over going up to the contralateral red nucleus or contralateral thalamus to the cortex okay so last thing i want you guys to remember here when it comes to kind of just because sometimes they can ask this in exam questions if i take the crust cerebri and the tegmentum does that make up something yes the crust cerebri and the tegmentum collectively make up what's called the cerebral peduncles so again i want you to remember that what are the cerebral peduncles the cerebral peduncles are a combination of the tegmentum and the crust cerebri okay a couple more things here one of the other things that is going to be coming out of the midbrain but it's in this area of the tegmentum is a cranial nerve what is that cranial nerve that's at the inferior colliculus level this is one of the only cranial nerves that actually crosses you know what this cranial nerve is this is the trochlear nerve so the trochlear nerve or also known as cranial nerve four so cranial nerve four or the trochlear nerve is going to be a motor nerve it carries motor sensations to the extraocular muscle of the eye and what is that actual muscle called that muscle is called the superior oblique and if you guys remember we've covered all of these cranial nerves in more detail in their their separate videos but this is the muscle that kind of does opposite of what you would think so superior oblique actually causes what it causes inferior movement of the eye so it actually causes kind of depression of the eye but it also rotates the eye inward and we call that in torsion so it does inferior movement and kind of rotates the eye immediately and that causes this intorsion type of movement okay so superior oblique now last thing that we have to talk about is this posterior portion here if i were to kind of do like one of these little thingamajigs i kind of make like a little dotted line here now this is separating the tegmentum from this last structure here this last structure which is primarily only consisting of the colliculi is called the tectum but one of the components of the tectum is the inferior colliculus right so we have the inferior colliculus at this level and the inferior colliculus is a part of your tectum but again remember the tectum is made up of two colliculi and what are those two colliculi it is the superior colliculi and the inferior colliculi okay so again you have to remember posterior portion here if we were to kind of jot down what this posterior portion is called anatomically this portion is called the tactum but again you got to remember that the tectum is made up of the superior colliculus and the inferior colliculus okay that covers all of the internal structures of this part of the midbrain at the level of the inferior colliculus now let's go ahead and talk about the internal structures at the super colliculus then what we'll do is we'll kind of tie together all the kind of general functions of these internal structures all right so we covered the midbrain cross-section at the inferior colliculus what i want to do now is cover that cross-section or that transverse cut but at the superior colliculus level okay so a lot of this is going to be kind of like a recap really quick right so again what is this anterior portion yell it out guys this is the crust cerebri what does it consist of medially frontopontine right in the middle is corticospinal and cortico nuclear fibers and then the lateral portion is going to be the cortical pontine but particularly from the temporal lobe the parietal lobe the occipital lobe right and again from medial it's going to be supplying the muscles of the head towards the middle portion i'll be supplying portions of the trunk and upper extremities and the outer portion of this middle chunk here is supplying the lower extremities right here we have the substantia consisting of the pars compacta pars reticularis pars compactor releases dopamine pars reticularis releases gaba right here we have the medial meniscus the trigeminal meniscus and the spinal meniscus but what's gone do you guys notice something was missing the lateral lumeniscus and we're to explain a little bit more why later the lateral lemoniscus ends or terminates at the level of the inferior colliculus we'll explain that a little bit later when we get into another diagram so again that's gone so the level of the superior colliculus what's gone the lateral luminiscus but you still have medial trigeminal and spinal okay now let's come back towards the center what do we have here we still have that mesencephalic nucleus of the trigeminal nerve right and again that was picking up proprioceptive information from the mastication muscles we still have the cerebral aqueduct which is connecting the third ventricle to the fourth ventricle we still have the periaqueductal gray matter we still have the medial longitudinal fasciculus which is connecting the vestibular nuclei to the third fourth and sixth cranial nerve nuclei so a lot of this is recap right so what here is different in the tegmental area what's different in the tegmental area is you notice these big red nuclei structures where the crossing okay remember i told you we had the red nucleus at the level of the superior colliculus and at the level of the inferior colliculus we had those descending rubra spinal fibers so guess what this guy is this is the red nucleus that's in the tegmentum and when it crosses it crosses right away and it's crossing in the ventral part of the tegmentum right because again from here all the way to here is the tegmentum this is the ventral portion of the midbrain dorsal portion of the midbrain so the red nucleus when it crosses at that level of the superior colliculus it forms a decussation what is that decussation called it is called the ventral tegmental decussation all right and that's going to help us to understand that once this deca states and moves down through the area of the inferior colliculus what is it going to move into those rubra spinal fibers beautiful let's move a little bit back now back here you have these blue fibers here what was that in the other diagram at the inferior colliculus level that was the tactospinal fibers now remember tactospinal fibers what is the tectum made up of superior colliculus and inferior colliculus the tactospinal fibers technically start at the level of the superior colliculus so what happens is this is our superior colliculus here the superior colliculus gives fibers and what it does is it moves ventrally so from the dorsal part of the midbrain it moves ventrally and as it moves ventrally it crosses okay and when it crosses it then moves downwards so then it's going to start moving downwards towards the inferior colliculus level when it moves downwards it forms those tactospinal fibers so here's what i want you to remember this portion here of the the actual midbrain where the tectospinal fibers are just starting to originate and then cross that is called the dorsal tegmental decussation so let's write that over here let's write it right here so again we're going to have our superior colliculus here and then what happens with those superior colliculi what do they do again they cross and then they move down as the tectospinal fibers or tectospinal tract this portion here where they decasate is called the dorsal tegmental decussation and then they will move down as the tactospinal fibers are tracked which we saw on the inferior colliculus level sweet deal okay so we've covered a lot of these structures so far so we hit this one we hit this one we already talked about the medial longitudinal fasciculus in the other video we got this brown neuron here what is this guy okay this guy here this brown neuron is a cranial nerve you guys remember what cranial nerve is at the superior colliculus level it is the oculomotor nerve so this nerve here this is the oculomotor nerve what cranial nerve is that you guys got to remember that that's cranial nerve three this is really important to remember a lot of lesions that are involved can involve this level of the colliculus i'm sorry i'd list this level of the midbrain the superior colliculus so again oculomotor nerve oculomotor nerve you guys remember from the video that we covered this this carries motor fibers but it's sematic motor fibers so that's only controlling skeletal muscle so this carries what's called general somatic efferent fibers okay there's a nucleus that's also really important which is associated with this oculomotor nerve and it's these green fibers you see these green fibers that are this nuclei here and it's moving with the oculomotor nerve this guy has one heck of a name so these green ones up here this is called the edinger westfall nucleus and this is going to be primarily carrying what kind of fibers parasympathetic fibers can't stress that enough so parasympathetic nervous system fibers but these can go to visceral components they can go to smooth muscle okay they can go to other different structures glands so because of that this is general visceral efferent fibers so again these fibers are general visceral efferent fibers so we have the edinger westfall nucleus and the oculomotor nerve okay these are going to be controlling a lot of the eye movements as well as pupil constriction with the eddinger westfall nucleus and a combination of the lens for near vision all right sweet deal we covered that guy one more thing that's a little bit different here and this this baby blue kind of guy here this baby blue guy we talked about in the visual pathway and the pupillary light reflex video and this guy is called the pre-tactile nucleus that should make perfect sense because again if i were to draw that imaginary line back here what is this portion back here the tectum right consisting of the supercaliculus at this level and then below at the inferior colliculus just in front of it pre is the pre-tectal nuclei the pre-tectal nuclei are important in the the actual pupillary light reflex so this is the pre-tectal nucleus and what do they do again what happens is they receive sensory information from the eyeball right from the optic nerve and what happens is from the optic nerve you get this structure called the lateral geniculate nucleus or the lateral geniculate body and from that fibers can go into the supercolliculus and go to this pre-tactile nuclei and what it does is is it provides stimulation to bilateral edinger westfall nucleus and then these eddinger westfall nuclei will stimulate these axons to go out to the ciliary ganglion and control pupillary movement what kind of things if you shine a light in somebody's eye what happens that pupil constricts right but because in the edinger westfall nucleus it stimulates both sides so if i stimulate the right and the left pupil by shining a light and let's say someone's right eye they're going to constrict the right pupil and the left pupil so that gives you direct and your consensual light response so that's the job of the pre-tactile nucleus it allows for that direct consensual light response beautiful okay we covered that last portion here so again we covered the cross cerebri we call it covered all the parts of the tegmentum last thing is a part of the tactum which is the we already should know this the superior colliculus so right back here in the tactum is your superior colliculus now the superior colliculus we already kind of described a very simple thing about it remember this receives visual information from the retina from parts of the cortex like your frontal eye field and your actual visual cortex in the occipital lobe it receives that information guess what else it receives information from from your sensory system right and it basically coordinates that to help us to play a role with what do we say tracking a moving object or something of that nature right so moving our head and our eyes with the object that we're following okay so that is the job of the superior colliculus now we covered all the internal structures what i want to talk about now is just the basic function of all of these internal structures we've already covered all of these things in great detail in separate videos let's get a general overview we talked about all these internal structures and it's good to just know these things obviously it's important to know these structures their names and their location but it's also really important to just have a general overview of what these things do and we've already talked a lot about some of these pathways in more detail that you guys can talk about we'll actually i'll refer to that as we go along so let's kind of get a general overview not going to go into crazy detail in every single thing just an overall function of all of these different structures okay let's start here with this diagram this diagram we're going to cover the lateral lemoniscus we already talked about that within the cochlear nerve pathway right so the auditory pathway but just to give you guys a little bit of information about it if you guys remember we have the vestibulocochlear nerve right and it's picking up sensations from the inner ear right from the spiral organ of corti if you guys remember and what happens is that information comes via the vestibulocochlear nerve to the level of the pons medulla junction and at that kind of like pons with dual junction if you guys remember you have a bunch of different nuclei okay called cochlear nuclei and what happens is these vestibulocochlear nerve it kind of synapses on some of these cochlear nuclei and then what happens is they end up kind of crossing into the other side right and whenever they cross to the other side they move up via this structure called the lateral laminiscus and this lateral limb meniscus guess what it does it eventually can synapse on the inferior colliculus which we said was right here so remember you have that lateral meniscus guess what it sends its fibers to terminate at the level of the inferior colliculus that inferior colliculus guess what it does after it receives this auditory information it sends this all the way up to the structure just outside of the thalamus you guys remember this from the auditory video this guy is called the medial geniculate nucleus or the medial geniculate body and then what happens is from here that'll then get kind of relayed to a part of the thalamus and then that will go to the temporal lobe right where the primary auditory cortex is you guys remember that that transverse gyrus of hessel right so that is kind of the overall point of this is that the lateral luminisk is carrying this sensory auditory pathway to the inferior colliculus and from the inferior colliculus that goes up into the medial geniculate nucleus and you actually kind of might want to know what this little connection is between the inferior colliculus and the medial geniculate nucleus this is called the brachium so they call this the brachium of the inferior colliculus okay so simple thing not a lot of detail i just want you guys to get an understanding of what this thing is okay next thing i want you guys to understand here is remember we said that you have that tactospinal fibers right well remember we said here that the inferior colliculus i want you guys to remember guess what it can do not only can it connect via the brachium of the inferior colliculus to the medial geniculate nucleus but it can also send information to your superior colliculus guess what your superior colliculus can do then if you hear something your superior colliculus activates that tactospinal pathway and it goes to the motor neurons that supply muscles of your head and your neck and it also can stimulate cranial nerve nuclei that can help with moving your eyes so someone yells stimulates your inferior colliculus he tells your superior colliculus guess what the superior colliculus does moves his your neck and your head and your eyes towards that auditory stimulus isn't that so cool so that's the job of this inferior colliculus kind of process all right so we talked about the inferior colliculus kind of a part of that right and we talked about this lateral lemoniscus let's kind of go back here we're going to take a step here and talk about these corticospinal corticopontine corticonuclear fibers and again we've already covered all of this in our descending pathways video but to give you guys a little bit of information remember you're going to have these upper motor neurons and they're going to be kind of situated with different parts of the cortex frontal lobe parietal lobe occipital lobe temporal lobe all of these things are basically going to be your upper motor neurons and they're going to send these fibers down all right and so it's going to move obviously through the internal capsule and then as it moves down through the internal capsule it's going to go through your midbrain right and remember what we said is these descending fibers will run through the midbrain and we kind of gave a clinical uh or a clinical correlation to that right so as these fibers move through the midbrain you guys remember that what happens as it moves through the midbrain it kind of goes down here to the level of the pons and in the ponds you guys remember we talked about this in that video you have a bunch of pontine nuclei okay a bunch of ponte nuclei located here and what happens is some of these cortical fibers may synapse on these corticopontine nuclei but some of them may scatter around that that pond new ponte nuclei and then move re kind of reconnect and then move back down through the medulla where they will decastate at the level of the pyramids and then move into the lateral columns of the spinal cord to go down and you guys remember that it'll stimulate the anterior gray horn right and from the anterior gray horn you'll have these lower motor neurons that will go to your muscles to cause contraction so what i want you guys to remember is the fibers that are going down all the way to your spinal cord these are the corticospinal fibers the fibers that may stop along the way and give stimulation to nuclei within the brain stem maybe it's a cranial nerve nuclei right so maybe this is a cranial nerve maybe it's like the the red nucleus maybe it is the uh another nucleus within the actual uh the brain stem but the fibers that are branching off and giving stimulation to nuclei within the brain stem those are your corticonuclear or corticobulbar fibers and then the fibers that are synapsing at the pons are called the cortical pontine fibers and just a very simplistic thing we talked about it a little bit in that video but these cortico-pontine fibers what do they do they decasate and they go via the you guys remember that structure that's between the pons and the cerebellum middle cerebellar peduncles and it connects to the cerebellum right so it'll connect to the cerebellum and tell the cerebellum here's the motor plane that the cortex set up can you receive all the information from the proprioceptors information from the proprioceptors from there information from the cortex information from the basal nuclear all these things and make sure that this movement is perfectly coordinated that's pretty cool right so again corticospinal going to the spinal cord the neurons at that level corticonuclear nuclei within the brainstem cortical pontine going to the pawns which will decasate and go to the contralateral cerebellum to make sure that the movement is properly coordinated and perfectly calculated okay all right so we covered this cross cerebri right and again i want you guys don't forget don't forget that anatomical orientation or that kind of like homunculus thing okay next thing we gotta talk about is the next part of the tegmentum that's substantia remember the substantia again we've already kind of covered this a little bit in the parkinson's disease video and we'll have another video discussing more of the basal ganglia but if you guys remember what happens is that the substantia has what's called the nigrostriatal pathway right so it has fibers that come up here and connect to the striatum and if you guys remember what that does is it helps to play a role within making sure that the motor movement is properly fine-tuned it's it's coordinated perfectly in such a way and so if you guys remember it's connected to a structure here within the actual uh the central next to the cerebrum and this guy is called the lentiform nucleus so you guys remember the lenti form nucleus the linty form nucleus is made up of you guys remember the putamen and then the globus politus externus and the globus politus internus right and then these structures are connected to your thalamus and there's also interconnections between all of these things and the caudate nucleus and there's even another structure involved here called the subthalamus well what the substantia niagara does is and we're not going to go into all date all the details in this but it's involved in two pathways the direct pathway in the indirect pathway remember the direct pathway will basically go to the cortex and help to stimulate motor movement and the indirect pathway will go up to the cortex and help to inhibit a particular motor movement what the substantia does is it releases dopamine onto neurons that are involved in the direct pathway and neurons that are involved in the indirect pathway and helps to kind of speed up the intensity of that motor activity so if you damage these neurons what happens you lose that kind of increased kick to the muscles and that can lead to parkinson's disease okay so again substantia has a connection via the nigrostriatal pathway to this lentiform nuclei which is involved in helping you to play a role within very meticulous fine-tuned kind of motor movements all right so we covered again the basal ganglia and it's very simplistic we're going to go into more detail in that in another video and we'll go into way more detail on the direct pathway and indirect pathway and all the glutaminergic and gabaergic neurons and all of stuff like that but fine and i just want you guys to get the basic point that the dopamine is released to help to kind of increase that actual motor activity so next thing let's talk about here is that decussation so now what we're going to talk about is that decision and we talked about a little bit i wanted to kind of make sure i clear you guys minds up on this completely the decussation of the superior cerebellar peduncle so again get your anatomy here situated right so we have midbrain pons medulla cerebellum and then we have our spinal cord right well in the actual cerebellum you have some nuclei we talked about this in the cerebellum video if you guys remember that mnemonic don't eat greasy food it's a dentate nucleus your emboliform nucleus your globose nucleus your vestigial nucleus primarily the ones that are involved in this these deep cerebellar nuclei is that dentate the globose and the emboli form and what do they do they send fibers here right remember what we said they sends from the cerebellum to what thing to the contralateral red nucleus so from here we'll have all of these deep cerebellar nuclei send their motor plan to the contralateral red nucleus what is the name of these fibers this is called the cerebello rubral fibers now what can happen is some of these uh fibers from the red nucleus will move up to the thalamus or some of the fibers may go directly from the cerebellum right cross over and move to the thalamus and this would be called cerebellophthalmic fibers so again you can have cerebellum rubra phthalic fibers cerebellar rubral fibers or cerebellothalamic fibers and all i want you to remember out of this is that from the deep cerebellar nuclei and again cerebellum is important for tone for coordination for posture all of these things it sends up your kind of like blueprint of the appropriate defined motor movement how does it get it up to the cortex though it sends it up via the red nucleus to the thalamus and then from the thalamus you can send this up to your motor cortex or it can go via the cerebellum to the thalamus and then from the thalamus up to the cortex so that is what's forming that decussation of the superior about cerebellar peduncles two primary pathways again cerebellorubral and cerebelothalamic all right so that is important thing to remember for this pathway another thing that can happen though is this is actually really cool not only can the red nucleus send things upwards but guess what else it can do it can send things down and it can send it to a nucleus kind of in the medulla region here called the inferior olives and if you guys remember the inferior olives what can they do they can send these fibers back into the cerebellum right so they can send these fibers into the cerebellum and when they send these fibers into the cerebellum they come in via the climbing fibers remember the climbing fibers and the mossy fibers and again this helps to play a role with really helping to coordinate proper motor movement okay so pretty cool here again that decussation is made up of cerebellum rubra or cerebello thalamic fibers all right guys so now let's talk about some other stuff let's talk about these luminous guy okay so the luminous guy if you guys remember we have the medial luminiscus and the trigeminal the spinal and we already talked about the the lateral luminiscus again we're not going to go into ton of detail here but i want you guys to just have an understanding basic understanding of what this is remember that dorsal column it's picking up sensations right from the periphery from proprioceptors which play a role within position of joints and tendons and muscles it's picking up vibratory sensations find a discriminative touch and it's sending it down this unipolar neuron into the dorsal gray horn and what does it do it moves ipsilateral into that dorsal column and then ascends up right and if you guys remember it eventually it comes here to about the medulla and you have those nuclei again we're not going to talk crazy about this but you have the nucleus cuneitus and the nucleus gracilis and what happens is these fibers eventually will cross right and then move upwards okay so again you have the dorsal column which is bringing up sensations right and when it comes up through the midbrain it's coming sensations from the contralateral side actually because it crosses at the level of the medulla right so again sensorations from proprioceptors from finding a discriminative touch and from vibrations are coming up via the dorsal column right and then synapsing on that nucleus cuniatus and nucleus or cells and then coming up via the medial meniscus through the midbrain and eventually this will go up to the thalamus and then to the cortex right so that's that job so that's coming up through that midbrain the other one which we'll do here let's just do this one in green for simplicity sake remember we have that trigeminal nucleus here remember that trigeminal nucleus here we have again the part in the midbrain which we already talked about which was the mesencephalic nucleus and then we have a part in the pons and then we have a part in the actual medulla well remember that this guy picks up sensations right from the trigeminal nerve so sensory sensations will come in via the trigeminal nerve and go to this nucleus right so there'll be sensations from the face this will come to this nucleus and what this nucleus will do is it'll give off fibers that are coming from the medulla portion of the trigeminal nucleus from the pons portion of the trigeminal nucleus and the midbrain portion of the trigeminal nucleus and it'll move up as an ascending tract and do you guys know what this little green tract is that's moving upwards this is the trigeminal lumeniscus so again trigeminal luminiscus so this is basically picking up sensations from the face right so the light touch pain temperature proprioception from the mastication muscles and coming into this trigeminal nuclei from the trigeminal nuclei it gives off these fibers that ascend upwards as this sensory tract called the trigeminal meniscus or the trigeminal phthalate tract and it'll go to the thalamus the last one that i want you to remember here let's do this one in red and we're going to bring it on this side here this guy is going to be a part of the spinal meniscus spinal meniscus picks up pain and temperature sensations right and it also can pick up light touch and pressure and what it does is it moves in via the dorsal gray horn synapses on that neuron there in the dorsal gray horn and then what does it do if it's the pain and temperature sensations what happens they cross over right and then when they cross over they move up via the lateral and if it's that kind of crude touch and pressure sensations that moves into the ventral and eventually kind of comes up but eventually these two fibers will kind of fuse together and as they come up they will come up as a tract and guess what this tract is called this is called the spinal luminiscus so you have the spinal meniscus you have the trigeminal lemoniscus and you have the medial luminiscus so this is just giving you guys a little bit of information again about how these tracks are working what they're carrying okay and again if you guys want more detail on these tracks go watch our video on these descending tracks all right so now we talked about the kind of the ascending fibers let's talk about some other things here i want to talk about those another descending remember the locus aurelius and the dorsal raphe nucleus remember we had those guys here kind of situated within the periaqueductal gray matter remember these we kind of drew these a little bit a while ago we named those right remember that we have that pain pathway so here let's draw that same thing here let's draw that same thing here you're going to have the these pain fibers right they're picking up pains and temperature sensations moving into the dorsal gray horn crossing over and when they cross over they move upwards via that spinal meniscus right what happens is you are going to have these structures here and this is going to be your locus ceruleus right and you have your dorsal rophae nucleus and what happens is these guys are going to send down their serotonergic and norepinephrine or noradrenergic fibers downwards and they're going to synapse at that area okay within the dorsal gray horn if you guys remember back from that video i'm not going to write the whole name out here now what the heck guys remember that substantia gelatinosa of rolando who comes up with these names but that's in that rex lamina right the rex laminate number three and the dorsal gray horn that's where that substance p is released right in that actual that space remember the substance p is important for that pain pathway their substance being glutamate which is for your slow and fast pain pathways remember the locus cyrillius and the dorsal raphae nucleus come down to this area and they release things like norepinephrine so they release things like norepinephrine and serotonin or 5-hydroxytryptamine which helps to stimulate specific little neurons in that area to inhibit this pain pathway so whenever there is a painful stimulus right so this guy is going to lead to a painful stimulus to send this up via the spinal meniscus this locus aurelius and dorsal raphae will send down descending fibers to inhibit this pain pathway so it's like our analgesic system our endogenous analgesic system isn't that so cool so again putting a little bit of uh background behind these structures here so again that's the purpose of the locus cyrillius and the dorsal raphae nucleus all right so let's talk about the next thing so we kind of finish a lot of the structures pretty much at that inferior colliculus level okay we'll talk about we'll talk about a couple other ones that are pretty much at both levels but now we're going to do is we're going to talk about this red nucleus which is at the level of the superior colliculus right okay so again superior colliculus level will have this red nucleus now if you guys remember the red nucleus gets stimulation from a bunch of different areas right you can get stimulation from the cortex and it can get stimulation from the cerebellum but basically what happens is when it receives this stimulation remember what we said it decasates at that level all right and it's in the dorsal part i'm sorry the ventral part of the tegmentum so what do we call that decussation ventral tegmental decussation and then what happens is is it descends downwards and it goes into the columns here right so and then what happens is when it goes into kind of your lateral white columns it gives off axons to the ventral gray horn and these ventral gray horn neurons will go out to muscles what muscles the muscles that are involved in flexion primarily of the upper extremities so again red nucleus to give you guys some context at the level of superior calculus it crosses ventral tegmental decussation moves its way downwards through the rest of the midbrain pons medulla goes into the spinal cord and the lateral white columns and then gives off axons it terminates on the upper the lower motor neurons in the spinal cord that are primarily serving the muscles of the upper extremities for flexion that's the rubra spinal tract okay next thing that we have to talk about here so another really important structure that is involved here is going to be the oculomotor nerve now if you guys remember we went into so much detail in an individual video about the oculomotor nerve or the cranial nerve three what i want you guys to remember is just because this is a lot of questions that they can ask on exams and it's also important clinically when we talk about midbrain lesions the third cranial nerve if you remember it supplies it has its general somatic efferent fibers those general somatic efferent fibers are supplying the skeletal muscles of the eye and if you guys remember that mnemonic right or they had like a little thing lr6 so4 pretty much and then all the rest three that's kind of the easiest way to remember the muscles that are supplied all right so we cover the super erections we cover the inferior rectus what else it got it's got that medial rectus baby right so we got the medial rectus remember that medial rectus helps with adduction of the eyeball so like like one of these things so it helps with that kind of motion adduction then you got the inferior oblique and remember the obliques pretty much tell you like opposite of what they you would think that they would do so they help to elevate the eyeball and they help to extort so kind of move the eyeball like this so extortion remember superior oblique was depression and in torsion inferior oblique is elevation extortion the last one is the eyelid you know the the levator palpebra superioris i'm not writing all that down so we're going to put levator palpabra superioris okay and that helps to just elevate the upper eyelid so these are the extraocular skeletal muscles that's supplied by the general somatic efference of the oculomotor nerve the general visceral efferents supplied by the edinger westfall nucleus which are those parasympathetic fibers are supplying the sphincter pupillae right so it's going to supply the pupil and when it supplies that pupil it supplies the sphincter pupillai which helps to play a role within constriction of the pupil so plays a role in pupillary constriction it also supplies this muscle here so we supply the pupil the sphincter pupilite and then we're going to supply these silliers and remember the ciliaris pulls on those ciliary zonials or the suspensory ligaments which helps to change the shape of the lens to accommodate it now remember what does the ciliaris do it pulls on those ciliary zonules or the suspensory ligaments which helps to change the shape of the lens which we call accommodation but what does it accommodate for near vision or far vision it accommodates for near vision okay so these are the things that i want you guys to know primarily when it comes to that third cranial nerve so we got that let's move on to the next thing which is the medial longitudinal fasciculus all right so the next structure i want to talk about just overall function is the medial longitudinal fasciculus okay all right so we guys remember that structure okay remember we had we talked about that with the vestibular cochlear nerve remember the vestibular cochlear nerve picks up sensations right from the inner ear primarily from the what structure remember we have the cristae ampuleris right which is in that semicircular canals the ampulla semicircular canals they come up and provide stimulation to what structures they provide stimulation to the vestibular nuclei within the kind of like that medulla pons junction okay what happens here is when they stimulate these vestibular nuclei you guys remember what happens is as they come up and they stimulate the six cranial nerve right so they're going to stimulate that sixth cranial nerve once they stimulate the six cranial nerve what happens is the six cranial nerve will then do what it'll kind of cross over here right and move upwards so it'll kind of move upwards and give a stimulation to the third cranial nerve so again vestibular cochlear nerve will lead to stimulation to the vestibular nuclei the vestibular nuclei will give off stimulation to the sixth cranial nerve the sixth cranial nerve will then give off its axon some of the axons will then move upwards on the contralateral side to the third cranial nerve same thing on this side your vestibular nucleus is going to stimulate this side of the six cranial nerve from that six cranial nerve it's gonna give off it's some axons that are going to ascend upwards and these are gonna give stimulation to the contralateral third nerve nucleus okay so now we have again we have the stimulation from the vestibulocochlear nerve to the vestibular nuclei to the sixth cranial nerve who will cross over and supply the contralateral third nerve and for vertical psychotic movement it can also supply the trochlear nerve so this is what i want you to remember whenever you're kind of moving your head to the right your vestibular nuclei will help to coordinate movements of the eyes appropriately so if i move my head to the right my eyes are going to kind of beat to the left in order to do that i might need the lateral rectus on one side to move in a specific way while the medial rectus of the other eye moves in the opposite direction right so whenever i move my head to the right when i do that my eyes are going to be to the left so the left lateral rectus will have to contract and the right medial rectus will have to contract okay so that's kind of how this all plays a role so again what is this blue structure here moving up through the midbrain to connect the trochlear third nerve and six nerve this whole thing right here is called the medial longitudinal fasciculus this would be the left medial longitudinal fasciculus and this one would be the right medial longitudinal fasciculus okay so it helps to control what's called the vestibulo ocular reflex or coordinated movement of third fourth and sixth nerve nucleus okay so that covers that guy let's move on to the next thing all right so the last thing i want to talk about since we've pretty much talked about everything else and again we already kind of went into a decent amount of detail on the pretecta nucleus if you guys want more detail on that one go watch our video on the pupillary light reflex it gives more information on that but again just wanted you to know kind of the overall direct and consensual response that it's involved in last thing that i want to talk about is the superior colliculus and we've already kind of talked a little bit about this one but again to give you guys a little bit of orientation here is a kind of like a little a frontal section or coronal sectioning of the kind of the brain stem and spinal cord so again here you have the midbrain pons medulla spinal cord and if you guys remember here's our cerebellum right so this is obviously superior colliculus and this is inferior colliculus and again if you guys want they might sometimes ask questions about this on like in exams what is the name of all four of these collectively called together and they call this here we'll write it down here it's called the copora quadra gemina okay but again the most posterior portion again of that midbrain like we said right here that's our tectum okay but again all four of these little structures are called the copora quadrigemina now if you guys remember we said that the inferior colliculi are getting stimulation from the ears so we'll just write down ears right so they're getting information from the auditory pathway and what happens is we already said that the inferior colliculus will send information to the superior colliculus well where else does the superior colliculus get information we said that the superior colliculus has come up to this diagram here on the sagittal section against supercolliculus inferior colliculus we said the superior colliculus gets information from the visual system so if you have a visual stimulus from the retina these fibers can connect to the superior colliculus guess what that is called whenever you have a connection from the retina as well as other structures so you'll have stimulation from the visual cortex and you can have stimulation from the frontal eye fields so again you'll have frontal eye field visual cortex and even stimulation from the retina and these things will converge onto the superior colliculus that connection between these to the superior colliculus is called the brachium of the superior colliculus now once the superior colliculus is stimulated guess what it can do again guys it can send its descending fibers to nuclei within the brain stem to control movement of the eye so your third your fourth or sixth nerve nuclei to control movement of the eyes and then it can also send axons down to the spinal cord which will go to muscles of the head and the neck so to give you guys a little bit of information from this again superior colliculus receives a visual stimulus so if kate upton's kind of walking down the street and you're like you're moving your head and your eyes in that direction okay that's what it's responding to then let's say her boyfriend's yelling hey you then look in his direction right because the inferior colliculus is stimulated when he's stimulated he tells the superior colliculus and says hey move your eyes now in the direction of where that auditory stimulus is coming from okay so that is kind of the whole function of this superior colliculus it helps with reflexive movements of the head and the eyes in response to a visual inferior colliculus movement of the head and the eyes with response to a auditory sensation okay and again it sends these fibers down as what remember what happens here supercaliculus will send across and i'll descend downwards into the axons here and go out to the muscles what is this tract here as it remember they have the dorsal tegmental decussation and then descends downwards as the tectospinal tract okay so guys we covered every single structure here that we can talk about within the midbrain that is more clinically relevant all right engineers in this video we talked about the midbrain and we covered a ton of information we talked about the anatomy we talked about a lot of the physiology and functions related to the midbrain okay and i know it was a lot of stuff i know it was very long and very detailed but i hope it made sense i hope you guys did enjoy it i hope you guys learned a lot from it in another video we'll get into more detail on the midbrain lesions like weber and benedict and claudette and even paranal syndrome because now that we got the foundation down we should be able to completely understand the pathophysiology so guys i hope you guys like this video if you guys did hit that like button subscribe comment on the comment sections go check out in the description box we have links to our facebook our instagram our patreon everything that you guys would want to connect with us we would appreciate it we love you ninja nerds and as always until next time [Music] you

Channel: Ninja Nerd

Views: 444,423

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Id: -3Pj5sNqf-Y

Length: 67min 20sec (4040 seconds)

Published: Tue Sep 01 2020