hi ninjas in this video today we are going to talk about the cortical bullbar tracks let's get started all right engineer so when we talk about cortical bulbar tracks we have a couple goals one to discuss where they begin what's their origin then what's their destination the end point then what is the function of the cortical bulbar tracks okay and then what we'll do is we'll draw out the cortical bulbar track kind of in a step-by-step process in two views a sagittal view and then a coronal view okay so first things first what is the origin of the cortical bulbar tractor where does it begin and that is your motor cortex right the motor cortex now the motor cortex is made up of a bunch of different areas right one of those is your primary motor cortex your primary motor cortex do you guys know where the primary motor cortex is it's on your pre-central gyrus this contributes about 40 i'm sorry 30 into your cortical bulbar tracks the other one is called your motor association cortex it's called your motor association cortex and your motor association cortex is made up of two of them right your pre-motor cortex and your supplementary motor cortex and they both contribute 15 so 15 for pre-motor 15 for supplementary that's a total of 30 percent to the cortical bulbar tract and the last one is going to be your your primary somatosensory cortex and if you guys remember this is the one that's on your postcentral gyrus and it's on the parietal lobe and this accounts for approximately 40 percent okay 40 percent of the corticobulbar tracks all right so ky we have an idea of where the origin of the cortical bulbar tract is coming from motor cortex-wise but then if we dig down a little bit deeper into that primary motor cortex take a coronal section from that motor cortex where on the homunculus right so if this is our homunculus that little man that we look at the motor homunculus what portion of that homunculus would be here well here you're going to have where the legs are right so this portion right here would be your legs your lower extremities this portion right here would be the trunk this portion right here would be the upper extremities and this last portion here that we're going to circle this is where the head the neck and the tongue muscles are all supplied that's where that's going to originate so when we talk about cortical bulbar tract it's from these motor cortex areas but from the what the most lateral and inferior portion of that motor cortex is where it begins beautiful so we know the origin the next component here is talking about the destination where do these cortical bull bar tracks eventually go to they're going to go down somewhere in synapse on something what is that destination what is this point here the first point that you need to know is it's going to synapse on the trigeminal nerve nucleus so what is the trigeminal nerve nucleus this is cranial nerve 5 and cranial nerve cell 5 supplies what your muscles of mastication right so this is your trigeminal nerve okay so that's one that we're going to start with your trigeminal nucleus the next one that it's going to go down and synapse on is going to be cranial nerve seven and this is your facial nerve and what does your facial nerve supply your facial nerve is going to supply the muscles of facial expression the motor output right so that's your facial nerve the next nucleus that it comes down to is actually a big old nucleus okay we give this nucleus a special name what's called the nucleus ambiguous now you're probably like well zach i thought we were kind of getting into a trend here where we were hitting specific nerves well the nucleus ambiguous is actually the nucleus of three particular cranial nerves one is cranial nerve nine and cranial nerve nine is your glossopharyngeal nerve right the other one is cranial nerve 10 and this is going to be for the vagus nerve okay and the last one here is going to be cranial nerve 11 but particularly the cranial part of the 11th nerve which is your accessory nerve so this is called your accessory nerve so the nucleus ambiguous is the nuclei of three particular cranial nerves glossopharyngeal vegas and accessory that's another destination point the last true destination point is going to be the hypoglossal nucleus so it's going to be the hypoglossal nucleus and this is cranial nerve 12. so this is called your hypo glossy nucleus now some people might say well zack i read in textbooks that it also supplies cranium nerves 3 4 and 6. it does but not directly cortical bulbar tracks go directly from the cortex to these cranial nerves but for cranial nerves three four and six it's an indirect connection right how is it indirect well it's cortical bull bar attract to two particular structures one is called the pair median pontine reticular formation and the other one is called the media longitudinal fasciculus these interact with third nerve i'm sorry the third nerve nucleus the fourth nerve nucleus and the six nerve nucleus so when we say cortical bulbar tracts these technically are not a part of the cortical bulbar nuclei okay if we're really being specific okay that covers our destinations so we understand the origin the destination points so if we focus on the destination out to whatever structure it's going to it should be relatively simple right so think about the cranial nerve five well we said that's the trigeminal nerve what does that supply i don't want to know every single muscle i just want you to tell me that muscle group it's the muscles of mastication that's your chewing muscles that's one thing that it's going to be involved in so the cortical bulbar tract is involved in that the next thing is it also innervates cranial nerve seven what is that nucleus that's your facial nerve nucleus what does the facial nerve supply that supplies the muscles of facial expression right i don't wanna know every muscle i just want to know that group so it's the muscles of facial expression a bunch of muscles in that group the next thing is the big one and that's that nucleus ambiguous which is a son of a gun dispel this guy again is a part of what three cranial nerves the cranial nerve nine which is glossopharyngeal cranial nerve 10 which is vagus and cranial nerve 11 which is particularly the cranial part of 11 which is an accessory all of these combined supply what things it supplies the soft palate muscles bunch of those it supplies the uvula thing in the punching bag in the back your throat the pharynx and the larynx and there's a bunch of muscles that are involved in that the next thing that there is involved in is the hypoglossal nucleus which is cranial nerve 12. and the hypoglossal nucleus is involved with the muscles of the tongue right so if you think about this when we talk about corticobulbar track it's involved in chewing facial expression muscles basically in your entire deglution process speech and movements of the tongue that is the function of the cortical bubble tracks now let's talk about the cortical pullbar track pathway in two views sagittal and coronal so let's start with each step if you were asked in an exam or by your attending hey tell me the step-by-step process of the critical bullbar track from beginning to end here's what you would say we're going to start with the cell bodies in the cerebral cortex the motor cortex right from here it's going to move down when it moves down it moves through this fan-like structure called the corona radiata then from the corona radiata it moves down through another structure called the internal capsule from the internal capsule it then moves down through the midbrain via the crust cerebri then from the cross cerebri in the midbrain it then moves down into the pons and then extends all the way down to the level of the medulla along the way it's going to give off its collaterals to these nuclei when it comes down and stimulates these cranial nerve nuclei what is this type of presentation or setup if you will this from the cortex to these nuclei this is kind of what's referred to as a upper motor neuron and then these nuclei here these cranial nerve nuclei all of these they're getting information from the upper motor neuron so these are technically all a part of a example of a lower motor neuron from each one of these nuclei when they're stimulated by this cortical bulbar tract it's going to activate these nerves cranial nerve five what's that going to go to muscles of mastication it's going to activate each individual nerve here what is this one the facial what is that going to go to repetition is good right muscle is a facial expression it's going to go here to the nucleus ambiguous what's the nucleus ambiguous a part of that's a part of cranial nerve 9 10 and 11 cranial part that's going to go to muscles of soft palate uvula pharynx larynx then the last one here is going to be the hypoglossal it's going to stimulate that and that's going to come out via this nerve to go and supply the muscles of the tongue that's that pathway in a sagittal view now we have to dig in a little bit deeper and talk about some ipsilateral contralateral pathways that you can't see in a sagittal view but you can see in a coronal view let's do that now all right so we talked about the sagittal view of this pathway now let's talk about the coronal view of this pathway so again where are we beginning we're beginning in that motor cortex where in the most lateral and inferior portion where the head the neck and the tongue and all those muscles are supplied so from here we're going to have all of these cell bodies in this cortex give off their axons these axons are going to fan out as a part of what was that whole fanning structure that we said here the corona radiata not the coronavirus the corona radiata and then from here it's going to move down the internal capsule now this is another discussion we didn't talk about it because you couldn't really see it in this sagittal view but you have the internal capsule right and then this portion here is the anterior limb this portion here is the posterior limb and then this portion here in the middle is the gnu right here in this gene where the bend of the internal capsule is where the cortical bull bar fibers run through then as they run through all this they come out here and then run where into the midbrain we're only following the right cortical bulbar track so this is the right cortico bullbar track that we're following the same thing is going to happen on the left we're just not showing it coming here through the midbrain via the crust cerebri which is this in this area it's going to move down through the midbrain and down through the pons now as it moves through it's going to extend where does it extend down from the pons down to the medulla all the way down here right along the way it's got to give off collaterals what were those collaterals well we said it gives it to the trigeminal nerve to the facial nerve to the nucleus ambiguous and the hypoglossal nucleus here's what we didn't see in the sagittal view we only saw one nucleus in the sagittal view there's two trigeminal nuclei so this is your cranial nerve five nucleus both the right and the left and the same thing is going to apply for all the ones below this will the right cortical belt will retract you know what's cool about this it gives off axons that go to the right trigeminal nerve nucleus that makes sense right but guess what else it does it gives it off to the other one too so it gives a ipsilateral collateral an ipsilateral fiber and a contralateral fiber that's to the trigeminal guess what else would happen you know how the left cortical bulbar tract would also be coming down this way it would also be giving a collateral to the left trigeminal nucleus and the right trigeminal nucleus that's very important so remember cortical bulbar gives bilateral to right and left trigeminal nucleus now we come down to the facial nerve nucleus it's a teensy bit more complicated this is our right cranial nerve seven nucleus and this is our left cranial nerve seven nucleus there's two parts right this is the upper portion and this is the lower portion it's very simple the upper portion of this nucleus supplies the upper muscles of your face the lower portion supplies the muscles of your lower face why is this important we'll talk about a little bit more detail later because it needs a teensy bit more discussion for right now right cortical bulbar tract remember we're only following the right it's going to give off it's ipsilateral fiber to the upper facial nerve nucleus it's going to give off a contralateral fiber to the left uh facial upper part of that nucleus here's where it's just a teensy bit more complicated the right cortical bulbar tract gives a collateral only to the contralateral lower aspect of the facial nerve nucleus that is important we'll go into a little bit more detail of them the significance of that later but that's that part it does not give an ipsy lateral to the lower portion follow the corticobulbar tract down more as you follow it down further you come to this nucleus ambiguous again it's going to give a ipsilateral connection to this nucleus ambiguous and a contralateral connection to this nucleus ambiguous so in the same way it supplies the right nucleus ambiguous and it supplies the left nucleus ambiguous and what are the three nerves associated with this cranial nerve nine which is glossopharyngeal cranial nerve 10 which is vagus and cranial nerve 11 particularly the cranial part of the accessory nerve so when we talk about the right cortical bulbar tract which is the only one we're following it gives contralateral and ipsilateral supply to the corresponding nucleus ambiguous go down to the last nucleus the hypoglossal nucleus when it comes to the hypoglossal nucleus again you have two parts the upper part of the hypoglossal nucleus and the lower part of the hypoglossal nucleus the upper part supplies muscles of the tongue other than the genioglossus the lower part supplies the muscles of the tongue only for genealogists this right cortical bulbar tract which is the only one we're following right now gives off a ipsilateral fiber to the right hypoglossal nerve nucleus the upper portion and a contralateral fiber to the upper hypoglossal nucleus on the left side so again which one is this one here this is your right pink this is your right hypoglossal nucleus which is cranial nerve 12. this is your left hypoglossal nucleus citrus cranial nerve 12. the right cortical bulbar tract gave a ipsilateral supply to the right hypoglossal nucleus the upper portion and a contralateral supply to the left upper portion of the hypoglossal nucleus again here's where it's a teensy bit complicated we have this lower portion for the right cortical bulbar tract it's only going to give contralateral supply to the left hypoglossal nucleus the lower portion only going to the genioglossus muscle so to simplify this if someone were to ask you these nuclei trigeminal nucleus and the nucleus ambiguous from the right cortical bulbar tract it's getting bilateral supply it's the simplest way of explaining it for the facial nerve nucleus it's getting bilateral supply from the right corticobulbar tract to the upper portions only contralateral supply right for the lower portion same thing for the the hypoglossal nucleus it's getting bilateral supply from the right cortical bulbar tract to the upper portions of the nucleus and contralateral supply only to the lower portion of the hypoglossal nucleus why is this important that i stressed on all of this we're going to talk about that in just a second but again where the pathway is not over we've taken it down to the nuclei once this cortical bulbar tract has stimulated something on these nuclei what does it do let's just take for example the nucleus ambiguous it stimulates the nucleus ambiguous activates the cranial nerves which one glossopharyngeal vagus accessory and they go out and stimulate what the muscles of the soft palate the uvula the pharynx and larynx same thing stimulate the hypoglossal this goes to muscles of the tongue facial muscles a facial expression trigeminal muscles of mastication so we followed the pathway all the way from the cortex down to the destination from these nuclear destinations what's the overall function now because these can be a teensy bit complicated we're just going to zoom in on a little bit and just talk about why it's so significant we know this bilateral contralateral supply for facial and hypoglossal alright so to finish up again i wanted to just kind of zoom in on the facial nucleus and hypoglossal nucleus because it was pretty easy for all the other nuclear they were getting bilateral supply from one cortical bulbar tract and they would get bilateral supply from the other cortical bulbar tract except for the facial hypoglossal they get kind of a bilateral and a little bit of contralateral so i wanted to discuss that so again kind of expanding here we have this facial nerve nucleus right here this is this is the cranial nerve seven nucleus this upper portion of the nucleus is going to the upper facial muscles this lower portion is going to the lower facial muscles that's the first thing i want us to understand when we look at this diagram this black part here is designed to represent the cortex okay so this is our cortex this portion here is meant to represent the nuclei so the facial nerve the facial nuclei and then here is meant to represent obviously the face so what's the step-by-step process we really kind of zoom in on it let's take for example the right cortex and then the left cortex and go step by step right cortical bulbar tract what do we say it's going to come down and it's going to do what it's going to give an ipsilateral supply to the upper facial nerve nucleus on the right side and it's also going to give contralateral supply to the left upper facial nerve nucleus but it only gives contralateral supply to the lower left facial nerve nucleus same concept follow from the left from the left cerebral cortex the left cortical bulbar tract is going to come down what's it going to do it's going to give ipsilateral supply to the left upper facial nerve nucleus contralateral supply to the right upper facial nerve nucleus and then only contralateral supply to the right lower facial nerve nucleus why is this important we're almost there from let's just follow the right side in this case from this right upper facial nerve nucleus this is going to go and supply the right half of the upper aspect of the face from the left this is going to only come down and supply the right half on the lower aspect of the face now if you damage you have a lesion that develops here in the left corticobulbar tract for example you have less supply going to these upper nuclei right because they're going bilateral but what is compensating for that loss of supply to the upper nuclei on the right and left of the facial nucleus the right cortical bulbar tract your right critical bulbar tract is still intact so it's still able to stimulate the contralateral upper facial nucleus and the ipsilateral facial nerve nucleus so this can still fire in other words this can still fire and send action potentials to the upper aspect of the right side of the face even though there may be damage to this tract that's important but here's what's interesting this tract we already covered the upper aspect but what about the lower aspect this left cortical bulbar tract is only going to the contralateral facial nerve nucleus on the lower aspect do you have the right cortical bulbar tract giving any supply to that no so because this black fibers are only going to the contralateral side on the of the lower facial nucleus on the other side you have no ipsilateral supply so therefore this is not this lower aspect of the right facial nerve nucleus is going to be inhibited it doesn't have any supply so because of that this will not be sending action potentials to the right lower half of the face so all of these muscles on the right lower half of the face are going to undergo either complete paralysis or weakness what does that mean the face will start drooping on the right side but the upper aspect of the face on the right side they'll be able to use those muscles and wrinkle their forehead because that tract going to the upper aspect of the face is intact because they have a contralateral supply so because of that why is this so important if a patient comes into the hospital and they have a drooping of the face what's your immediate concern a stroke well it's they're going to have drooping of this this face but you have to determine is this a stroke or is this bell's palsy how do you do that well in bell's palsy you take out the entire facial nerve nucleus that means the upper part of the face isn't getting supply and the lower part of the face is not getting supply and a stroke where you take out this upper motor neuron the critical bulbar tracks you still have the muscles of the upper face on the contralateral side still intact but this lower part is damaged so you'll droop but then what you what do you tell them wrinkle your foreheads ma'am or sir they'll be able to do that and that could be a sign of a cortical bulbar track lesion rather than bell's palsy that's why this is so important to know all right so we covered the facial nucleus now let's cover the hypoglossal nucleus because the same concept occurs so it should be quick look at the hypoglossal nucleus right this is going to be the nucleus of cranial nerve 12. the upper portion supplies the tongue muscles right but which tongue muscles the tongue muscles other than the genioglossus so not genioglossus so supplies all the tongue muscles except not the genioglossus the lower portion of the hypoglossal nucleus supplies only the genioglossus that's the first thing that we have to establish upper all the tongue muscles except genoglossus lower just the genioglossus now let's take the same example here here is your right cortex here is your left motor cortex here is the hypoglossal nucleus this is your right hypoglossal nucleus this is your left hypoglossal nucleus this is the right half of the tongue this is the left half of the tongue okay if we follow this step by step right cortical bulbar tract comes from the right cortex right makes its way down as it comes down what did we say before it gives bilateral supply to the upper portions of the hypoglossal nucleus but gives only contralateral to the lower aspect of the hypoglossal nucleus the same concept would apply for the left cortical bulbar tract which we're going to do here in blue it would come down it would give what ipsilateral supply to the upper portion of the hypoglossal contralateral supply to the upper and then only contralateral supply to the lower hypoglossal nucleus same concept you whack out that left cortical bullbar tract you take it out it's done now follow this through if the left cortical bulbar tract is injured it's not going to be able to give enough supply to the right upper hypoglossal and the left upper hypoglossal nucleus right via this thing one and two you're not going to get enough supply so this right cortical bulbar tract thank the lord it's still intact and it's still able to fire and still stimulate the left hypoglossal nucleus the upper portion and the right hypoglossal nucleus the upper portion so even though this left cortical bulbar tract is damaged your right cortical bulbar tract can still supply the upper portions of the hypoglossal nucleus due to the bilateral supply but this third part here this left corticobulbar tract again it's damaged it's not going to be able to stimulate the right lower hypoglossal nucleus this will be inhibited right do you have a supply coming from the right corticobulbar tract to compensate let's follow it no because it also goes to the contralateral so there's no black fibers coming to this hypoglossal nucleus on the lower portion so therefore if we follow this through only this part only this hypoglossal nucleus here which is going to the genealogist muscle we'll just say right here and then you have same thing coming over here from this left genioglossus muscle okay if this genioglossus nucleus isn't getting enough supply because you damage the left cortical bulbar tract it's not going to be able to fire its action potentials and because it's not able to fire its action potentials it's not going to be able to stimulate your right genial glosses this left genioglossus nucleus right or the left hypoglossal nucleus the lower portion it's intact because there's no problem with the right cortical bulbar tract it's still firing so because that it's still going to be stimulated it's still going to be sending action potentials and your left genioglossus muscle is still going to be getting some stimulus here's what's really interesting your genioglossus muscles when they contract they protrude your tongue out but your right genioglossus when it protrudes it protrudes it a little bit towards the opposite side and then your left geniogloss is when it contracts it protrudes it a little bit forward but also towards the right side if i knock out the lower hypoglossal nucleus i mean if i knock out my left cortical bulbar tract which means i don't stimulate my right lower hypoglossal nucleus i don't stimulate the right genioglossus that means that this movement here is gone i can't move the right genome i can't stimulate it to move the tongue forward and to the left now the left genioglossus is the only one firing and because it's the only one firing when it protrudes the tongue it's going to protrude it more in its direction because this muscle is weak or paralyzed so now look at the deviation if it's moving this way what way would the tongue be deviating with respect to the lesion the contralateral side so that's important so if you see someone who has contralateral tongue deviation you want to think a corticobulbar track lesion all right so that covers that and that covers the cortical bullbar tract in general ironers so in this video we talk about the critical bull bar tracks i hope it made sense ninjas we love you we thank you as always you know what to do until next time [Music] you