16. Motor systems and brain states, part 2

the following content is provided under a Creative Commons license your support will help MIT open courseware continue to offer highquality educational resources for free to make a donation or view additional materials from hundreds of MIT courses visit MIT open courseware at ocw.mit.edu I want to go over the uh homework I will post right after the class I wanted to talk talk to you about it first these are really worksheets It's homework that you should all get everything right uh I will do a separate homework that will make up for some of the bad quiz performances I know you requested that that's not what this is this is to help you review and uh I selected a bunch of pictures I'm just giving you it this will all be posted uh I guess uh do you all do you all have access to printers if you have problems printing it just uh come with us after class we'll print it for you but I'm going to show you what it is this these are the worksheets and you can see if we look at one of them here this is a pretty straightforward one that you should remember remember now uh here you have places to uh to write the names and so to just to remind you what I want here in question one I say in slide number one that refers to the number of the slide is that okay the number is actually written in the corner okay and then I list ABCDE E I just want you to write the the English and the Greek or Latin okay for each of those subdivisions that's what you do for that one okay and uh for something like this all all of these are like that here I ask you to to name the parts that the that are being pointed to here I ask you to color in the pathway like I did in class and I want a local reflex Channel okay now whereas this they're blank brain diagrams they're pretty similar to the ones I used in class but they match the text of the book uh very well so and then I ask you questions about them so but for those because you have to if you have to draw on it notice I put it put it right in those are the ones you would need printed and for this one too because I'm asking for drawing uh and then I ask the question up here here I want you to draw a primary sensor neuron I've already drawn it for you on the horizontal uh diagram there but I want you to do that here too and I want you to show the spinothalamic track and then later I do the same thing for the I column and medial liscus and then I do the same thing for the cortical spinal so you can find those figures they're all in the book they were all in the slides too and uh and I want you to draw them in but if all you're going to do is find it and then go back and forth to get every detail right you're not learning much you have to study it then put it aside and then try it try to draw it and if you hand something in that's with all kinds of things crossed out because you didn't write it that's all right I want you to use it to learn about these things some of these might be on the midterm okay or I might just ask questions about them but yeah there might be things like this on the midterm definitely okay so that'll all be posted and that is just to help you review we can have it due Monday I think and I will get another one posted where you just have because these are all very straight PR you just have to find them learn them try to do it you know some of many of them are they I give you the diagram and I want you to I've eliminated a lot of the labels you know so like in the one with the meninges and the Gia you know you should know which ones here are the as sites which is the Duro is what is the pan what is the the uh Ira noid so you need to know those things and it's good to have have it not just the words but have it in your spatial memory too so that's why we're doing it use it to to practice and review and then I will give you some questions I think mostly on the motor system because you haven't had any homework on that and I could give a little bit on development things that I know you can find and uh we'll use that as I promised to make up for bad quiz grades we'll decide exactly how we're going to do that but I think that's fine all right so let's 17 17 through the brain States chapter then we do the start sensory systems afterward afterwards after the break or wait a minute do we have a Friday I guess there's a we started start it just before the break all right so this is where we were uh it's a little bit more on the a little bit more in the introductory chapter to the motor system where we're talking about uh these uh multi-purpose movements there was a lot about Locomotion last time um we've also talked about the other movements uh all that I have what remains is I discuss a little bit about uh evolution of that ability and just because we know that the tectum is the dominant structure now in most animals except perhaps in animals like humans and even monkeys where the cortexes become so dominant over most of these functions but in most animals it is still very important and has an importance even in humans More Than People realize so I do mention a little bit about uh some of the early controls and I then I but I'm mostly emphasizing two very different functions of the tectum one involving Locomotion we talked about Escape movements you know uh but normally when animals are escaping they also Orient they don't generally Orient with respect to the animal they're escaping from they Orient towards safe places if they're near their tunnel they head for the tunnel if they're near any Hiding Place uh any place they can crawl into to get away they head for that and they're extremely good at finding that very very rapidly and I say a little bit about the tectum and pretectum here because I go over this in the visual system later on if I were you I would just read this uh and use it it it does help prepare you for what's coming but we right now you need to know this the different major outputs the tectum okay so a little bit more about grasping we know why it's so important uh we know what muscles are involved we know that there's different kinds of grasping grasping with the hands we know in primate large primates it's largely a neocortical function but animals without neocortex can still feed themselves they still have to grasp things either with the mouth or with the hands uh so structures evolved to do that and they're in the midra so that's what those questions are about uh and we talked about this a little bit last time so I'm not going to go over it again uh but I didn't talk about the red nucleus in a little more detail there's two major parts of the red nucleus and it's quite interesting when you compare different animals there's a large cell part in the that's the coddle part of the nucleus and then there's a small cell part so we refer to the magnos cellular red part of the red nucleus it's abbreviated NR for nucleus rhar and then MC for magnos cellular or NR nucleus rubar PC for parvo cellular parvo means small okay so those are the two parts and it's really interesting if you look across uh the primates and even if you went here to primitive primates it would be like the carnivore here in humans the parvocellular part the rostal part is by far the largest part the magnos cellular part is smaller so what do these two parts do well the out outputs are very different and of course their inputs are different too let's just deal with the outputs the the rubos spinal tract okay the output to the spinal cord that comes from the large cells the magnos or part of the red nucleus so in animals where that pathway is more important more important than neocortex it'll be like this the codal part is relatively larger that's true in carnivores it's true in rodents true in most animals but animals that have really developed um more endbrain control of their hands then the powerful cellular part is more so why is that well what does IT project to first of all it IT projects forward not like the rubos spinal tract this this projects Rost paracellular nucleus uh projects to the thamus mostly to the ventral lateral thamus the part of the thalamus that projects to the primary motor cortex okay and it also projects to the precerebellar nucleo so the inputs to the cerebellum and to the neocortex depend on that for control hand movements go through that carb cellular part and this also shows a correlation with a structure in the cerebellum it's this structure they just pick that out of the cerebellum it's the lateral most deep nucleus it's the part of the cerebellum that gets input from the very large hemispheres in human cerebellum but any animal what they're not showing here is the whole cerebell or hemispheres growing bigger uh in these animals at the right in apes and humans and also monkeys whereas in other animals with less of this kind of control that lateral cerebellar output nucleus is also smaller so as the cerebellum evolves so does the cortex and the red nucleus changes also um I'm know having I animals no because animals can still be pretty dextrous without so much visual input but it there is a there is a general correspondence uh if you look there are prosimians for example that where the red nucleus is more prominent than it is even in humans uh that have incredible dexterity but it's mostly fixed action patterns they use it for grabbing bugs out of the air you know so all the animals I mentioned that have a small one are less visual you have these different types of cells in other systems too but no there's no real strict correlation animals can be very dextrous even without using vision and humans without Vision can very very dexterous sand movements all right so there's interesting there's an interesting study of of the projections of the red nucleus because they're they're in concerned with control of distal muscles well there's distal muscles in the for limbs but also in the hind limbs so the question is are those kept separate in the red nucleus so you look at the projections to the cervical enlargement and the lumbar enlargement this is just a cartoon to illustrate uh those two parts of the spinal cord and then the red nucleus projections and what this shows is neurons that project to the cervical enlargement neurons that project to the lumbar enlargement and neurons that project to both they have a an a branch to both nuclei so if you look at look at the osum you'll see that there is some inter mixture here the topographic separation of the represent presentation for hand control and foot control is is not all that good in the rat it's a little better and in the cadets the separation is really good and of course in primates it is too just an interesting thing about how you find these correspondences with function and Anatomy uh in these descending projections okay so now I want to talk about the outputs and I'm I want to start with the motor neurons uh so then we can talk about the pathways that connect to those motor neurons and how the pathways save from the cortex and brain stem connect to the motor neurons the spinal cord and the we're talking here about sematic motor neurons okay we talked earlier about autonomic and we've said a little bit about Nur endocrine control through the hypothalamus we talk a lot more about that when we talk specifically about hypothalamus we're just talking about the sematic system with synaptic connections to muscles not paracrine as in the autonomic system and not endocrine as in the endocrine system so this is Lor Swanson's ha ation of the entire motor system he says the three motor systems this is the sematic number three here number one is the endocrine and he shows this the dash line indicates connections there's no synapse at all they're just through the bloodstream and then the paracrine intervation of the autonomic system parap sympathetic and sympathetic that's motor system 2 and motor system 3 and when he discussed is that it's interesting he says we don't know what are the uh what are the pattern generators that are coordinating these three systems and my comment about that is just that we don't know if there is very much direct coordination centrally of these systems but there probably is some but it's not then specifically we know a lot less about that than we know about control of pattern movements okay and this just distribution of sematic motor neurons uh I've had that in other pictures that I showed you early on that you probably didn't pay much attention except I always showed the motor neurons ventrally so I asked this question here this is a horizontal view it doesn't indicate anything about dorsal and ventral so I say where are these neurons located in frontal sections so well here this is all spinal cord where most of those neurons are and you can see most of them are in the enlargements because there's many more muscles to control in the limbs and we need finer control so we've got more motor neurons controlling them they're always in the ventral horn and that's what we're going to talk about uh next but these are the groups of neurons in these columns that aren't directly connected with each other that we talked about when we talked about hindbrain and midbrain and notice the most rostal ones are in the midbrain that came up did it did come up a couple times in the class if you didn't remember fine but with the help of the quiz you'll probably remember it now the most rostal sematic motor neurons if you include the endocrine system as motor and like Swanson does then you could say well there's another kind of motor n in the hypothalamus and even even further forward okay secretory cells we're not talking about secretory cells now at all just control of sematic motor neurons all right so I want to talk about it's a chapter centered on the studies of descending Pathways they the anatomy and their function and these are the ones we just saw I want to answer this question now what's the basic spatial layout of motor neurons at one of the spinal cord enlargements how is it organized and then we'll talk about what connects to those motor neurons and the main type of neuron that connects to them is interneurons in their intermediate layers of the spinal Court yes there are some coming directly from cortex 2o and we'll talk about those uh those connections connect mainly to those interneurons okay and this this is a kind of figure you often will see in a medical school book what does that mean is that Atlas holding the world up no it's he's holding a spinal cord up but why do they have him pictured like that with his arms like this because it's showing that the motor neurons in the ventral horns here the motor neurons controlling the axial muscles so the muscles of the neck or the along the back those are the axial muscles control very important in postural control and uh they're most medial and then we talk about the girdle muscles the muscles that control shoulders or hips okay separate from the muscles controlling the limbs uh you find those next moving laterally and then the arms and finally the hands and feet depending on whether you're in the cervical or lumbar enlargement okay so this is the picture from the Lawrence and pyer study that I use in the book it shows a a section of the spinal cord and it it just by just putting in a few neurons they're showing you groups of neurons that are located medially and then more and more laterally and uh so axial muscles medially then the girdle muscles and then the distal muscles and there is some separation that you see in that other picture of the flexors and extensors as well okay you don't need to worry about flexor and extensor extensor separation because it is fairly complex there's no need to memorize it okay but you need to know about the relation of the topography in the chord and the control of different muscles in the body okay so now we know about prox IND distal represent in the cord the next question we'll go back to this one is the interneurons and yes they are radially arranged so the inter neurons way out laterally here do connect to the lateral most motor neurons where's the ones located imediately connect to the medial ones controlling axial muscles and there's another difference that's quite important some of those inter neurons that connect to the medial motor neurons project both sides of the cord because when you control axial muscles you're always dealing with movements that are never they always involve both sides of the body so both sides of the cord tend to be involved okay and the same thing is true for descending connections connections that go to those that are for the control of axial muscles tend to be bilateral that's a very important point if you're studying studying doing lesion studies the function okay so then in this study by it's a classic study by uh henriquez tyers a very well-known neuroanatomist a Dutch neuroanatomist a colleague of Na um and his student Lawrence that did this study back in the 60s published it in brain and everything they found applies pretty much to humans as well and corresponds to many findings in the clinic okay but what this the upper section show here are the patterns of termination of first of all at the left the cortical spinal tract or the part of the cortical spinal tract coming from precentral gyrus the motor cortex okay and it shows that it goes everywhere if we include the post Central gyrus then you'll see it goes to the dorsal horn too so pretty much everything and it also crosses the midline this is just the left cortical spinal track it goes to both sides but only in that ventromedial area the part that controls the axial muscle muscles okay so then he's got Pathways that travel through the come from the lateral brain stem including the red nocus the midbrain and they travel laterally through the hindbrain they're joined by axons from lateral reticular formation cells okay and they terminate in this dorsal lateral part of the interneuronal group they tend to spare the ventral medial area for the most part and they generally don't cross the midline then if you look at the medial Pathways medial Rin stem I'm calling ventromedial here because they're terminating ventromedially in the cord they that's where You' the tectospinal pathway terminating the vestibulospinal the ones from the cerebellum the pigos spinal and medial reticular spinals a lot of lot of different groups of axons send their axons always down in these medial regions of the vental column and they terminate in that pattern again if you just look at projections from the left side here they terminate more on the left than the right but they terminate bilaterally okay so now we can we can draw pictures like this to represent these three descending Pathways from cortex from the lateral brain stem and from the medial brain stem okay and I have this in color in the book so a little easier but all I do is show an a monkey brain with the enlarged spinal cord so we can see it a little better just separate the ones coming from the representation in the motor cortex of the body axis that is the back and neck and then representation of the limbs these are not this is a common mistake that most of your compatriots that don't take this class will make these are not motor neurons remember the defin how do we Define a motor neuron an axon that leaves the central nervous system and terminates on an eector organ usually a muscle okay those are the true motor neurons these are Pathways that among other things connect with motor neurons but most of them go to inter okay and if it's motor cortex they're usually concerned with movement but they go other places too they go to the cerebellum they go to the part of the inter neuronal um the great network but but now to describe okay so I separate them on these two diagrams and you just notice the ones controlling distal muscles which I've drawn in solid line here uh I show show them I show them in blue and book they they're terminating mainly in the enlargements so in the two enlargements you see them here too and see the color helps a lot you don't it's a little harder to separate here but it's the concept is very simple okay and then we I show here the position of those corticospinal axons here they are throughout the paramal tract in the hindbrain here in the midbrain they're in the middle portion of the Cal pet unle the other ones are going to terminate before they get to spinal cord a lot of them in the the pontine gray all right so here I showed the rub the tech the rubrospinal axons which cross and travel then they move laterally as they descend and here they are in the hind R right out here at the lateral lateral Edge so now the axon's controlling the more distal muscles if the anatomy is giving us the right idea can be found in those two places here and here coming from the except if I want these to correspond I have to say here and here because these haven't crossed yet these have crossed okay that's just that's a detail to keep in mind okay so and then here for the medial Pathways I show The tectospinal Crossing and then the vestibulospinal are uncrossed okay because they're hindra okay and I could have added the the ones from cerebellum I do show a few from reticular formation here that are joining that pathway and those are the ones that go down through the cord and terminate the ne intermedial region and here I show them in the cross-sections tectospinal I just showed the tectospinal and and the reticul spinal Origins here the disbo spinal is only on this one all right so so then what are the three lesions that lawren and kypers made let's just go through the logic of lawren and Kyper study very straightforward they did try just eliminating the medial hindbrain Pathways or the lateral Pathways and otherwise intact monkeys they didn't get long lasting effects at all so they reason that the re that probably that's because the cortex is so dominant and they had spared the whole cortical spinal pathway so they always started by eliminating Pathways from cortex they cut the paramal tract yes you have to talk Lou this this ventilation is pretty lck the type yeah you do get some recovery but remember there's a lot of different Pathways involved here and it's very difficult to get all of them you know and also there so there's various ways the brain can compensate but it's remarkable how little the compensation is when they do a really good leion and then I ask uh the functions of these three major Pathways well when I I introduced it with the outputs you can pretty much predict the function so we're going to go through through that uh and I want to know why would diis effects of lesions of one of the descending Pathways in the study be greater in humans than in monkeys so we'll come back to that when we talk about these these functional effects of the lesions this is their logic you eliminate the cortical clinal projections they did that at the hindbrain L by coming in through the roof of the mouth I've done this also in hamsters with a student cine C who's been at the University of Wisconsin now for many years I don't know if anybody else has attempted that in these little animals but we did and we succeeded to do it at least unilaterally but we you can see you see this in the Sheep Ranger section you can see the paranal track if the problem is you also see this huge artery called the Basler artery so what we do and also there's other problems when you're doing that kind of surgery you tend to stretch nerves in the neck and that can cause them to pull their breath in and hold it because you're eliminating normal Pathways involved in breathing so what we found is if we just flood the whole area with ice cold sailing we reduce the conduction so much in those nerves that they they keep breathing just fine and then then we take a little spatula nudge the Basler artery over and we have a little spatula like knife very sharp we know exactly how deep to go and we can do what Lawrence and kypers did here here's their lesions cut the paramal track this is the level they cut it they're making a cut from the ventral side just cutting the parameter tracks and usually just above the paramet tract is the medial medial liscus so they often did cut damage medial liscus fibers so because of that they had to have controls where they had lesions for example the dorsal column nuclei so they didn't they got rid of the medial miniscus fiber so they could see that the functional effects they were seeing in their monkeys weren't caused by the medial liscus damage okay and then they allowed them to recover from that lesion as much as they could and then they did one of these two lesions either they cut the lateral pathways on one side and remember that doesn't it stays on one side so you can compare the two sides of the animal or they they did the medial Pathways they tried it unilaterally didn't get much effect but if they did it bilaterally then they got drastic effects so this is what they're doing they'll going right through the damaged paramal track and it's already degenerating remember from the earlier lesion and they cut all those medial Pathways they all descend right near the midline yes yeah that's a good question there's there's a little a little bit and it's somewhat variable it's not as much as in humans but there is some lateral dominas there is some asymmetry in the brains too the most drastic asymmetry they found though in animals is in fish in the haban OR nuclei and they don't still don't know a whole lot about why that is okay so here's what happens you start with the Pam paramid aomy you get rid of those cortical spinal fibers you do it bilaterally initially they seem almost paralyzed and if you do this I here the question refers to this is the diasis effect because they recover a lot from it but why is that effect so much greater in humans remember it's just quantitative the pathway is bigger in humans the motor cortex is even more important in humans so humans after a paramal track section you know lose even their spinal reflexes for a well clear that's just like spinal shock transction to spinal cord but the monkeys lose speed and strength and they never completely recover normal speed and normal strength uh but they do recover a lot okay humans recover their strength they never recover full coordination uh but strength they do pretty well in fact sometimes the reflexes become overactive stronger than normal because of sprouting that happens in the spinal cord but the one thing they do lose that's that's a qualitative difference from normals is they can't do that anymore they can't pick something up with single digits they have to use their whole hand together so apparently those latal brainstem pathways are quite capable of controlling fairly organized hand movements but when it involves separation separate control of the digits they never really recover all right I mention here a question that I think I should give as a homework but you will just see a discussion in the the book I'll try to remember this since I'm telling it to you now there is a discussion of fixed action patterns of it's comes the only study I know of is I did with a student Katherine Cayla the woman I mentioned uh we found that they need the paramal track coming from cortex to do their fixed action patterns of seed shell so read about that and you can answer this question this the corrium for any kind of learned movements yes but in this hamster study we were looking at unlearned movements the first time they ever see I we raised them in the lab so you can they never they only see food pallets they never see seeds and yet the first time I give a hamster a seed I can let him become an adult and I can give them a seed and they can pick it up and shell it faster than you can because it's a fix it's inborn there are aspects of the sequence that are learned but most grooming is unlearned and uh so you don't get a permanent disruption uh there's some very good Studies by John Fentress if you look his name up he said El Housey University he's done many studies of grooming in mice uh genetic effects as well as lesion effects and showing that they are fixed action patterns this second question number seven here it refers to a study of motor system by The Beat Lab here at MIT so U read that and uh see if you can figure out I think I make it clear there in the book and this one we can deal with right now you should know what best cells are does anybody remember and I want to know how it's related to discovery of frit and H who are they 1870 the first guys to study motor cortex by electrical stimulation they defined it as the area which when stimulated it was a horrible time in Neuroscience because they didn't have good anesthesia at all okay so it's very difficult to do these experiments they actually did some of it on humans men in the Frank oppression War who had had their skulls blown off and so they were dying soldiers they still did some of this work that you know they were their first purpose was Medical but then they were able to do a little bit of this at the same time but most of the work was done on dogs and they were able to uh map out the motor cortex it's where with the smallest electrical currents you can get movement it doesn't mean you can't get movement from other places in the cortex you can they're descending connections from visual cortex too they don't all go to motor cortex most of them they don't go at all the motor cortex but they do go to the brain stem they go to the tectum for example so they control our anti movements directly from visual cortex by projecting to detect them so that's a type of motor cortex too but what we call the motor cortex is the specialized somat sensory area rostal to the primary sensory cortex in mammals okay B cells are the giant paramal cells that you find in that area that sh hitc mapped out as the motor cortex it was just four years later 187 1874 that bets described these giant cells they are the cells that give rise to the very long aons that go all the way down the spinal cord and they no doubt include neurons that project directly to motor neurons no no they're just the really big ones some of them are much bigger than others you see bed cells even in the hamster when we did those sections of the parameter tract and we looked at the motor cortex we wanted to know if the bet the the big cells or any cells degenerated and they didn't degenerate they just lose weight they get smaller they don't look as much like bet cells but we did cell count so we know that all the cells are still there they just get smaller when they don't support a long accent anymore okay just very quickly the medial lesions and this is described in the book you've got to do the lesion bilaterally remember the reason is because they cross over many accents do cross over but you get drastic effects on writing they did get some recovery why do you think they recovered you asked me this earlier even after as much as 40 days because there's other ways to write just with spinal reflexes the the input from the somat sensory system and from the joints can support some writing okay but the vestibular spinal tract is gone so they can't use do the normal means or tectus spinal also so they can't use Visual and they can't use C sens the distributor input to write anymore so when they walk they stumble around they don't know which way to go it's not I shouldn't say that they know which way to go because they still control our eye movements and you can see where they're looking you can see where they're trying to get to but yet they can't make their body do it it's a very interesting kind of you don't really call it a paralysis but they clearly can't control those movements well at all okay and then the lateral Pathways they lose we'll talk we'll come back to this and talk a little bit next time the way the way they did it I actually have films of this but it's I I need to see if we can find something online and so I could show it in class the video the the films take forever to set up and show in the classroom that was a very nice study sorry ocular M they're both true because the ocular motor the most rostal ocular motor nuclei are in the mid brain so either one is correct