Lecture11 Central Nervous System

hi everyone this is lecture 11 central nervous system so we are gonna talk today about the central nervous system in particular the regions of the brain and the spinal cord in the end we will then bring this all together to review the sensory and motor pathways that we began to introduce in the previous lecture lecture 10 when we talked about sensation so the nervous system again is the master controlling and communication system of the body the role of the central nervous system is integration so it is taking the sensory information that comes in through the cranial nerves or through the spinal nerves of peripheral nerves through this spinal cord are directly into the brain and then processing that information we can process independently in the spinal cord or the information can travel to the brain and be processed in the different regions of the brain so overall we have nearly gone through just about every part of this diagram for the nervous system so last time we talked about sensation of stimuli through sensory receptors going through the afferent nerves either the spinal or cranial nerves today we're going to talk about the brain and the spinal cord we will finish up by talking about the efferent nervous system or motor output either to the skeletal muscles or to the organs through the autonomic nervous system so if we look at this in a very simple circuit diagram we start with a sensory receptor we go through an efferent neuron to activate a central nervous system neuron which sometimes is indicated as an inter neuron from there then with some motor commands out to the efferent neuron to have a response in an effector muscle or gland so the central nervous system tissue is very easily damaged it has to be well protected from trauma and from harmful substances so there are three ways to protect the brain and the spinal cord first are the skull and the meninges second is the cerebrospinal fluid and third special to the brain is the blood-brain barrier so first and you should have learned all of these structures in your anatomy course but just as a review there are the bones of the skull which protect and surround the brain so here you can see the skull covered by the scalp and the hair once inside the skull there are tough connective tissue membranes that wrap around both the brain and the spinal cord you can see them here around the brain so this thick white layer is the dura mater which is the outermost layer of the brain in between the dura and the innermost layer is the arachnoid layer you can't really see much here but we will zoom in in just a moment the arachnoid layer then leads to the Pia mater which is right on top of the brain tissue the cerebral spinal fluid is another way that the brain is protected so the cerebral spinal fluid is formed by the choroid plexus is in the ventricles and those are shown here where you can also again see the layers of the dura arachnoid and then the pia will be right on top of the brain these indentations here are part of the arachnoid and they are called the arachnoid villi so cerebrospinal fluid is formed by cord plexuses and it's about 125 to 150 milliliters total surrounding the brain in the spinal cord and it's replaced about three times per day serve no spinal fluid one creates a fluid cushion a the brain that will absorb sudden shock if there's any sort of jarring movement so so head trauma stopping quickly knocking your head on something so very jarring movements where the brain might jiggle in the fluid the fluid keeps it from moving too much the other way that the cerebrospinal fluid protects the brain is to have very limited exchange between the cerebral spinal fluid and the blood so the exchange of materials and fluids between the cells and the glia and the interstitial fluid is very very tightly regulated to make sure that the central nervous system has very low potassium outside the cells high sodium outside the cells and very few proteins compared to the blood this all occurs because of the blood-brain barrier so the blood-brain barrier is a highly selective network of specialised capillaries that prevents substances from entering the brain there's a layer of capillaries that have tight junctions those capillaries are surrounded by astrocytes there's a large astrocyte star-shaped glial cell here and ependymal cells so the ependymal cells protects the brain by preventing most substances from entering so it prevents blood-borne pathogens from getting in so bacteria etc certain hormones from entering in certain toxins from entering the brain it is anything that is lipid soluble or oxygen carbon dioxide alcohol and water can cross the blood-brain barrier but other substances such as glucose amino acids and ions that the brain does need will have to be actively transported by the very selective membrane carriers if there are no carriers for a particular substance then that substance cannot enter the blood-brain barrier so one of the reasons for the tight regulation of the blood-brain barrier is that neurons have a very specific metal like requirements they are reliant mostly on oxygen and glucose for their metabolism so the oxygen can diffuse across the blood-brain barrier and under normal circumstances glucose will be the only energy source for neurons the glucose is transported from the plasma into the fluid by insulin independent membrane transporter so insulin is not required for glucose to get into the brain low blood glucose or hypoglycemia can lead to confusion unconsciousness and in the extreme case even death so if the metabolism of the central nervous system is oxygen and glucose what type of metabolism is that think back to your metabolism lectures yeah so it's aerobic metabolism that we've studied that occurs in the mitochondria requiring oxygen and glucose okay so functions of the brain now so we are going to get into the individual regions of the brain once we finish the brain then we will talk about the spinal cord so the brain overall is regulating homeostasis it is sending commands out to the body and listening to what is happening in an outside of the body to be able to respond appropriately with the right commands it is also regulating emotion movement control sensory perception memory and cognition are what we refer to as higher thought awareness and judgment so what I want to remind you of is that the central nervous system is functioning as a circuit so even though we're gonna go through one area at a time and I'm gonna show you guys you know generally what the function of a particular region of the brain is these functions are dependent upon the whole circuit so there are connections coming in that form its input their connections going out that form its output and it's really as a whole that these areas functioning so even though we look at each area individually I want you to remember that it is only one part of many of the connections that make up an entire circuit of information flow throughout the central nervous system but before we get into that we have to review a couple of terms so the gray matter in the central nervous system we refer to as nuclei so these are mostly cell bodies synapses dendrites neuroglia so a nucleus if we talk about for example the red nucleus down in the brainstem then that is a group of cell bodies in the central nervous system of ganglion is a group of cell bodies in the peripheral nervous system when we talk about nerves we're referring to the peripheral nervous system and that's white matter or myelinated axons connecting regions of the peripheral nervous system if we talk about tracks that's myelinated axons within the central nervous system so if you take a frontal section of the brain you will see regions of gray matter that appear to be darker sometimes pinkish sometimes grayish in color and regions of white matter that are myelinated axons sometimes crossing over to different regions of the brain and connecting different regions of the brain so I am going to present the brain regions as functional brain regions the alternative is to do it as a developmental organization and I prefer not to do that so we are going to start from a top-down view from the cerebral cortex all the way down to the brainstem so we're going to go from the cerebral cortex to the basal nuclei to the thalamus then the hypothalamus cerebellum and the brain stem and go from there so if you remember your general anatomy you may remember depending on how your instructor presented it to you this outer region of the brain is the cerebrum here we have a big landmark which is a huge white matter structure of the corpus callosum there's one of your ventricles which will contain so Oh spinal fluid that is one lateral ventricle and then below that I always call this the seahorse so let's see if you guys believe me this looks like the head of the seahorse there's the nose or the cheeks of the seahorse there's the pointed nose of the seahorse here would be the neck of the seahorse belly tail do you see how this all looks like a seahorse here and then this region in the back that sort of feathery looking structure is the Thera bellum so the seahorse type structure are what we refer to as the lower areas of the brain so we have the cerebrum on the outside and then here we have the thalamus which makes up the head of the seahorse here below the thalamus is hypothalamus on this diagram it's cut off it's not shown but on other diagrams you will see that hanging down from the hypothalamus will be the pituitary it would be right around here and then the neck of the seahorse would be the midbrain the belly of the seahorses the pons and then the last structure before we get to the spinal cord it's the medulla oblongata all of those three structure structures the midbrain pons and medulla make up the brainstem so first we'll start with the cerebral cortex so the cerebral cortex is the largest outermost region of the brain if divided into four lobes that are colored here in different colors so the front of the cerebrum is the frontal lobe the side of the cerebrum right around where the ears would be is the temporal lobe the top side is the parietal lobe and then the back of the cerebrum the occipital lobe this down here is the cerebellum and there's the brainstem underneath so when we look at the lobes of the cerebrum we have some major dividing anatomical marks so right here dividing the frontal and the parietal lobe is an important division which is the central sulcus okay the cerebrum can be divided into primary and other areas so we generally refer to these as primary cortex areas so the lobes of the cerebrum have different functional regions for the integration of the information that is being processed within the cerebral cortex often the cerebrum is just shorthand referred to as cortex you'll hear that a lot so primary regions are responsible for very simple direct and conscious processing of a single type of stimulus or command so for example you will see within the occipital lobe there is an area called the primary visual cortex the primary visual cortex takes in vision information from the eyes and have simple processing of light on and off is there light or is there no light and simple patterns of light entering the eyes the primary visual cortex is going to respond very simply to light stimuli and then you will see other names for cortical areas within the cerebrum so we have the primary auditory cortex that will respond to simple sounds so different pitches of different tones of sounds coming in through the ears the primary olfactory cortex is going to respond simply to smell the primary somatosensory cortex will respond simply to touch stimuli in different areas of the skin sensations general senses and then the primary motor cortex is going to be a simple motor command out to skeletal muscle so these are simple processing areas that have one singular function either vision or auditory oral factory etc and they will be then the first to stop for cortical integration after that information will then get processed to higher and higher areas before it ends up becoming a response so we have higher sensory areas so that would be more elaboration and processing of sensory input and then Association areas it will be even further integration of sensory input so in general we refer to these as complex cortical association areas so these are regions that are next to or near the primary cortical areas that will integrate multiple sensory stimuli multiple motor stimuli at memory and emotional stimuli integration so the best example I can give you is if the primary Association area is going to give you a pattern of information a pattern of lights then the Association area visual Association area will be the actual recognition of the image that you see so the primary Association area will be the light of primary Association air the primary visual area will be the lights and the different patterns that you're looking at and then the visual Association area will be the processing of that image say that is my grandmother that is a picture of my grandmother you'll also have auditory associations or factory association areas where you're going to bring in all of the other sensory and emotional and memory stimuli and put it together with that basic primary information to say oh that's my grandmother and now I'm going to associate it with all of the other wonderful things that are associated with my grandma you know the smell of her spaghetti sauce of the cookies that she makes all of that kind of thing so we have visual association areas auditory association areas olfactory somatosensory then we also have association areas or specialized areas for motor and these are generally sort of planning decision-making areas for movement so we have premotor cortex which is planning and deciding what movements we'll be sent out the primary motor cortex we also have emotional areas that have complex emotional and social processing so there's an area called the prefrontal cortex that will be higher-order emotional processing in the front of the brain then we have language areas which are more complicated sensory and motor areas some 4 movements to speak some for listening to speech and some for looking at or reading speech so there are some diagrams this is from a different textbook but I love this image and it's nice that it's color coded that will actually show you where these different areas are you may be wondering how do we know what these areas do so the way that this is actually done is that various different recording can be done of the cells in these regions particularly from human epilepsy patients or patients that have tumors they have done human surgical recording because they need to identify areas for tumors where they'll go in and they'll put an electrode in a certain region of the brain and they'll map it out and when they stimulate here the patient will say oh I see flickers of light and so that's going to be primary visual cortex or when they stimulate here and the patient will say hmm I hear a song that I remember and so that would be an auditory Association area so one by one let's go through the lobes and I'll show you the major areas in each of the lobes of the cerebral cortex so the occipital lobe this area in the back has the primary visual cortex which will be based at division and light it's going to receive sensory input from the retina which contains the photoreceptors in the eye its function is the perception and processing of light and then this area nearby will be the visual Association areas which will be more complex processing of visual information for example once I see that light I can then process the pattern of that and say oh that's a cat or that's my grandma the temporal lobe is the lobe here it's been pulled back to show another lobe the insula but the temporal lobe is here and the the main regions in the temporal lobe are auditory areas so there's a primary auditory area here and then auditory Association area nearby so the primary auditory area is going to be the basic sensory input from the ears so the tones of the sound waves that are coming in and then the auditory Association area will be the more complex Association of interpreting that sound into context that's my favorite song or that's a dog barking or or something like that in the frontal lobe then we have some major motor areas so if you find the central sulcus here which divides the red and blue regions of this diagram the central sulcus and forward all of this is the frontal lobe so the first region or this precentral gyrus contains the primary motor cortex and this is basic voluntary control of skeletal muscles these neurons cross over before they head down to the muscle aren't down the spinal cord to the final motor neurons controlling the muscles because of that this left side of the brain will control the muscles on the right side of the body and the right side of the brain will control the muscles on the left side of the body so we call that contralateral control where if a patient has a stroke that is affecting the left side of the primary motor cortex that patient will have paralysis or lack of movement in the right side of his or her body in front of the primary motor cortex we have some more complex Association areas we have the supplementary motor area what chops with sequences of movement so maybe ballet dancers might have a very good stuff limb injury motor area the premotor cortex which does a lot of learned and planned movements then behind the central sulcus or in the post central gyrus we have the primary somatosensory cortex which now were in this blue region in the parietal lobe so all of this is parietal lobe and the first part of the parietal lobe is primary somatosensory soso Maddow for body and sensory sensation so these are your general senses so general processing and perception of body sensations and proprioceptive input from your skin joints and muscles behind that area we have the somatosensory association area which will be more complex pattern so the primary somatosensory cortex might be there's a touched felt on my finger the association of the somatosensory association areas might be oh that is something soft or that is something rough or I feel a blanket that might be more of the association or attributing the texture and shape of something that you're holding for example so to look at it from the top view I wanted to show you guys again here's our dividing area which is the central sulcus and that divides the frontal from the parietal lobe the pre central gyrus is your primary motor cortex and your post central gyrus is your somatosensory cortex in the parietal lobe if you take a little cross section of these areas what is super cool is that as the information it's coming in to the somatosensory cortex from different areas of the body it will have these labelled lines that we talked about when we talked about sensation so the fingers the hands the arm information is all going to travel up particular nerves to go to a particular area of the somatosensory cortex your feet legs so they're all going to travel up particular areas to in particular parts of the somatosensory cortex so if we take a little piece of the somatosensory cortex here and we record along it or ask what does this area respond to then we find what's called a homunculus so here in blue there's your parietal lobe again and if we march through the parietal lobe with different stimulation electrodes or different recording electrodes and find out what each each area responds to we find a little map where the inner regions of the somatosensory cortex our feet ankles legs the outer regions are gonna go more towards face nose lips the middle region will be hand fingers etc and this looks like a tiny little human when you mapped it all out because it's mapping out the whole body and that's why it's called a homunculus or a tiny human we have the same kind of mapping that happens for the motor commands that are sent out to different control of skeletal muscles and it's interesting it's very similar matching on the other side but these will be nerves that are going to be excuse me tracts and the nerves that will be exiting out of the body but we have a similar map on the side where we have toes feet on the inner part of the primary motor cortex and or excuse me hands neck I face on the outer parts of the motor cortex and areas that are larger tend to have more brain space dedicated to them and so these areas will be more sensitive so you know that your lips are very sensitive your fingertips are very sensitive your forearm not so much and we're actually going to test this in lab so here's a closer view of the somatosensory homunculus if you're curious there and here's another closer view of the motor homunculus or the tiny map in the motor region of the brain also in the frontal lobe in addition to the motor areas we have what's called the prefrontal cortex right in the very front of the brain I hadn't pointed out to you already this diagram is a patient facing to the left so the eyes would be here the ears approximately here this would be the back of the head this would be the front of the head so the prefrontal cortex is right in the front of the brain so um this is an area that's involved in social and emotional planning and integration now that's something that's very difficult to test but we know from patients that have damaged to the prefrontal cortex that they have very strange and unusual emotional and social behavior so it's very interesting case studies about patients with damage to their prefrontal cortex so this area is involved with intellect reasoning judgment concern for others personality traits and management of emotions it develops much later in life and it's impacted very much by social environment it's very tightly linked to emotions and the limbic system which I'll show you guys in a bit another specialized group of areas in the cerebral cortex are the language areas so these are near and dear to my heart because what I studied for my PhD were similar areas for birds so birds in addition to having birds just like us have little speech areas but they have singing areas not speech areas so leaves for humans are the speech areas and we have one here which is between the temporal lobe and the frontal lobe this is Broca's area and this is for speech production so it's near the regular motor area and this is for actually doing the muscle coordination of tongue mouth lips vocal cords required for speaking and then here is an area called Wernicke's area and I remember this one could actually sometimes when you look at it in the diagrams it looks like a little ear and it's here on the back of the temporal lobe here and it is involved in actually listening to or processing the speech and language so in order to speak properly we have to both hear and process the speech and we have to then send out the appropriate commands and I studied this really similarly in birds so birds don't have Broca's area and for an acute area but they have singing areas that take up a good portion of their brain so that's what I if anybody is curious about what I did in my research I studied singing areas of the third brain so I think the language processing areas are a great example of thinking about something from a circuit view so here we have primary auditory cortex which is important for hearing words and then that will combine with primary visual cortex which will send vision so seeing words both of those primary areas will send information to Verna keys for speech processing so Verna cues is kind of like an association area but because we know very tightly what it does we can give it a special name for speech processing so once we listen to and read words we can then respond to them through Broca's area so Verna cues will send information to Broca's area which we can then use to send commands to the primary motor cortex which will send commands out to the muscles tongue and facial muscles to actually speak so we can summarize the areas of the cerebral cortex in this diagram and since we went through each one very very carefully I'm just gonna leave this diagram in the powerpoints for you guys to refer to later alright so from the cerebrum then let's get into the other areas of the brain so just below the cerebrum are the basal nuclei sometimes also referred to as the basal ganglia this is gray matter deep in the cerebrum and the basal nuclei are important for integration and fine tuning of motor sensory and emotional input so many functions the basal nuclei and and their research is continuing on the basal nuclei but we know a lot about the basal nuclei because they are affected in Parkinson's disease if you know anybody who has Parkinson's disease they generally have it tremor and they have a tremor when they stop and start movements so if they're going to reach for something a typical Parkinson's tremor will be they have really hard time initiating a movement so I have a tremor as they're initiating but once they start the movement they're good and if you think they then try to stop the movement they'll have a tremor or difficulty stopping the movement so Parkinson's effect this coordination which is to stopping starting in intensity of movements that would be coordinated by the basal nuclei between the basal nuclei in the cerebral cortex there's a lot of sensory motor processing in addition in the basal nuclei and some new research is looking at a region of the basal nuclei called the amygdala for emotional processing particularly in the fear response some autism research some PTSD post-traumatic stress disorder research thorough looking at the amygdala now for emotional processing so in behind and below the cerebrum is the cerebellum cerebellum kind of means a tiny brain so it looks like this tiny little brain behind the cerebrum so the cerebellum is also important for movement and what it is important for is balanced movement planning and movement execution so if you're ever watched the way of baby walks you will see that babies don't have a well-developed cerebellum takes a couple of years for the cerebellum to really learn all of the appropriate things that needs to learn so if you think about the way that a baby wobbles and it's out of balance that is all because the cerebellum is not fully developed yet so the cerebellum is important for balance and movement planning and execution it's very highly folded region just below here's your occipital lobe back here in the back of the brain to do this it has to receive visual body where your body is in space and cortical input and it is subconscious we don't we don't have any voluntary control of the cerebellum so the cerebellum will take sensory input from proprioceptive and vestibular or equilibrium pathways and put that together with information from the motor cortex or what movement planning is is being created in the cerebrum and it will coordinate what movement you want to do with where your body is in space and put that all together to create fluid coordinated movements so people with cerebellar problems will also have tremors but they will have different tremors and Parkinson patients they will have constant tremors okay um now we get into the lower regions of the brain so we did cerebrum there's a little piece of it there there's cerebellum there basal ganglia you can't see in this diagram you need a different section to see the basal ganglia but they would be sort of gray matter deep to the cerebrum and now we're gonna go below this corpus callosum or this big white matter structure into the lower areas so this region here is the thalamus this is what I was calling the the head of the seahorse so the thalamus you will see a lot because all of the sensory information not all but most of the sensory information that comes into the has to first be gated by the thalamus so we call the thalamus the gatekeeper it is going to filter process and decide whether sensory information is important enough to send up to the conscious processing regions of the cerebral cortex so there is a lot that we are unconsciously filtering out that we don't pay attention to because the thalamus is not sending it up to the cerebral cortex so it is filtering processing and relaying sensory information to the cortical regions it's basically screening or it's if the gatekeeper for sensory information deciding what should be passed on to the cortex and where what areas should it go to visual or auditory regions of the brain the hypothalamus is a tiny but very important area of the brain that is below the thalamus it controls in general homeostasis and of course that is a huge function but the way it does that is linking the nervous system to the endocrine system and to the organs so there's endocrine and organ or autonomic input directly to the hypothalamus to regulate the internal body environment so these are all the functions of the hypothalamus it is the autonomic or the organ control center in the brain so it is going to send the autonomic input through the brainstem and the spinal cord out to the organs it also has some basic emotional functions it can regulate body temperature sleep-wake cycles hunger water balance and thirst and secrete various hormones to the pituitary so we get into the endocrine system I think you guys will have an even greater appreciation of just how important this tiny area of the brain is and and we're just beginning to scratch the surface now okay we also have a system in the brain the limbic system that is an emotional processing part of the brain so it is a circuit of several regions including the basal nuclei the thalamus particularly the amygdala and the hypothalamus there is also association cortex that seems to have a general emotional region within the cortex so the limbic system is a sort of newer research system that we are currently seeing more and more research going on because of the interest in autism and PTSD and and other emotional emotionally or social related disorders and what we believe the limbic system is doing is affecting motivation basic emotions social behaviors sexual behavioral patterns basic survival and instinctual behaviors for example if you stimulate this part of the limbic system or the amygdala the patient experiences sensations that they will report as fear sensations so really fascinating area the limbic the limbic system okay so below the hypothalamus now I can get into the the last region of the brain before we get into the spinal cord so this is the brainstem which is made up of the midbrain the pons and the medulla oblongata within the brainstem we have something called the reticular activating system this is the fascinating part of the brain that is basically another filtering area so this reticular formation region is important for attention and arousal of the cerebral cortex there's some control also of sleep-wake cycles so what the reticular system or the reticular formation is doing within the brainstem is sending impulses out generally to the cerebral cortex to increase attention and increase arousal states the midbrain then is the superior portion of the brainstem and it contains a couple of structures that you may remember from your anatomy course on the back of the midbrain called the superior and inferior colliculi the superior colliculus is an important region of visual reflexes the inferior colliculus is an important region of auditory reflexes also within the membrane many many white matter tracts of axons going to and from through other regions of the brain the pons is this bulging region then between the midbrain and the medulla this anterior or in front of the cerebellum sits this region here so within the pons there are many areas but one of the most important areas we will hear about is the pneumo toxic respiratory Center which works with the medulla to maintain rhythmic breathing then the last bit is the medulla so last but not least the medulla is a very important region of the brain which is the base of the brainstem so it contains large motor tracts so large white matter that will cross over before they continue down the spinal cord both initially came from the primary motor cortex so there's going to be information traveling through the medulla to control skeletal muscle there are also the olives the medullary olives which will send information to the cerebrum and cerebellum so you'll see those in some of the pathways between the cerebrum and cerebellum and then they're very important organ or autonomic controlling nuclei or regions within the medulla you will hear about the cardiovascular center which adjusts heart rate and blood pressure and you'll hear about the respiratory center which controls the rate and the deaf the breathing and works with the pons together for rhythm there are other regions of the medulla that have other important reflexes for example the vomiting reflex the swallowing reflex coughing sneezing hiccups all of those reflexes are controlled by different regions within the medulla so we did a top-down view and we can work our way up now so from the medulla pons midbrain up to the thalamus hypothalamus with the cerebellum off to the back of the brain the basal nuclei would not be shown but they are pulled out here so you guys can see them in the diagram and then the largest region of the brain that the part that gets the most press because it's the conscious or the part of the brain that we have awareness of is the cerebral cortex I'm going to leave this here for you guys as a summary figure that summarizes the major functions of each of these regions of the brain so this is from your textbook table 5 to page 145 so the last thing I'll say about the brain before you move on to the spinal cord is that it can exhibit plasticity so the architecture of the cerebral cortex or the organization of the cortex so like the mapping that I showed you where the different areas are is determined by genetic and developmental processes but there are some really fascinating research going on right now that shows that the organization of the cortex can be modified due to how much activity if in a particular area so we call this use dependent competition so for example there's some really interesting research in blind patients that are obviously not using the primary visual cortex because they cannot see so there's no retinal input to the visual cortex the brain doesn't just get rid of that area the brain uses that area and other areas will creep in on the vigil area so for example they've found in some research studies that auditory information will be found in the visual cortex of blind patients so really fascinating reorganization that can happen based on how the brain is being used there can also be formation of new pathways and connections between existing neurons and some regions of the brain can be remodeled throughout life this research is ongoing we don't know how strong the remodeling can be yet or how often new area or new cells can actually stay within the brain but their research is very cool so if you guys are interested in that something you might want to check out ok so the brain is one part of the central nervous system the other part of the central nervous system is the spinal cord so the spinal cord is the pathway between the body and the brain and we already discussed this in our sensation lecture it contains the ascending and descending nerve tracts of the central nervous system relaying information to and from the brain it can also on its own initiate basic reflexes completely independent of the brain so just like the brain within the spinal cord there are maps of information and a cross-section of the spinal cord has many functional areas some going up to the brain which would be a sending and some going down from the brain or descending so we could talk about these pathways for a very long time there are many of them the mapping of the spinal cord is something that if you get into for example in your health sciences career if you get more into spinal health the mapping of the spinal cord is fascinating we're not going to get into every tiny region the spinal cord but I am gonna show you some examples so in general what we talked about in the sensation lecture is that sensations come in through the dorsal spinal cord so here is a muscle stretch receptor sending information to the dorsal spinal cord that information is in traveling up the spinal cord through the brainstem to the cerebellum or up the spinal cord through the brainstem and then up to the thalamus to the cerebral cortex so now you know that the sensory information can be gated by the thalamus or it can be gated by the brainstem where the medulla and then that information then depending on how strong it is can be related to the cerebellum to help with movement coordination or it can be related to the cerebrum to be aware of the sensation and then further decide whether we should have a response and then the primary motor cortex will send out commands descending down through the brainstem they will cross over to control the opposite side of the body and then go out of the ventral root of the spinal cord to control skeletal muscle so the gray matter and the white matter regions of the spinal cord can be very carefully mapped based on these sorts of pathways where we have the sensory information coming in to the dorsal part of the spinal cord the motor information coming out of the ventral part of the spinal cord and then in turn neurons within the gray matter and then tracts ascending or descending tracts within the white matter of the spinal cord so the dorsal horn contains the cell bodies of sensory neurons the excuse me contains the cell bodies of interneurons on which the sensory neurons will terminate the lateral horn will contain the cell bodies of autonomic and efferent nerve fibers and the ventral horn will contain your efferent or motor nerve fibers so in areas of the spinal cord we see a large lateral horn that's where you have a lot of input going to the organs this mapping I'm going to leave for your curiosity but I'm not going to test you guys on every tiny region of the spinal cord I just find that some students really want to know if you have a spinal injury that's this deep what would you effect if you have a spinal injury that's this deep what would you effect what if you were to section the entire spinal cord or have a damage to the entire spinal cord what kind of injuries could you expect so these are the kinds of pathways that you see throughout the spinal cord ultimately the spinal nerves will exit out of the spinal cord through the intervertebral foramen and there are 31 pairs of those if you want to review of these you'll want to return to your Anatomy and go back to the sensations lecture there are dermatomes are specific regions of the body that are intimated by specific spinal nerves though these are important clinically and damaged which particular spinal nerve or a dorsal root ganglion in a particular region of the spinal cord will produce a specific pattern loss because of this mapping that's maintained throughout the spinal cord so for example if you have a patient that is complaining of pain in the pinky ring and middle finger that's radiating up the wrist then you can generally excuse me that the ring finger and the middle finger that is radiating up the wrist and you can say that they may have damage to a nerve in the c8 region if they have damaged she's a pinky finger that is radiating up the elbow then you can look at the spinal t1 spinal nerve so these maps here's the front of the body here's the back of the body can ultimately show us how the the mapping of the spinal cord then is created by the mapping of the nerves we also the cranial nerves which connect directly to the brain rather than through the spinal cord and if you want to review these go back to your sensory lecture or your Anatomy slides so overall we have sensory motor and reflex pathways that are involving the integration of the central central nervous system so a sensory pathway is sensory input to the spinal cord and brain it's going to provide information on internal and external changes in the stimuli it is an efferent and a sending pathway motor pathways are motor responses based on a central nervous system decision so what is happening within the cerebrum which can be voluntary or involuntary meaning we don't know that it's happening to change activity in the skeletal muscle organ or gland these are efferent and descending pathways finally a reflex is a simple pathway that involves only the brain are only the spinal cord and this involuntary it's a very fast predictable motor response to a simple sensory stimulus so let's go back to our sensory and motor pathway example and draw them out so that we can see how you guys are following our overall circuits ok so we will start first with the sensory pathway so what you will have is in this example where we say a thumbtack right so there's this dark thumbtack that pierces your skin so here's your stimulus and that causes pain that pain is going to travel through the spinal nerve through the dorsal root ganglion and into the dorsal Horn of the spinal cord so there's your dorsal Horn there's your ventral horn one side of the spinal cord there's the other side of the spinal cord there let's draw the whole spinal cord around it so through the dorsal root ganglion and then into the dorsal Horn of the spinal cord and that information is then going to be sent up the a ferrant sensory pathway in this case is going to travel up the brainstem up through the medulla cross over and then head to the thalamus from the thalamus it will then be sent to the primary somatosensory cortex and that is where we had that homunculus within the postcentral gyrus of the parietal lobe so we have a painful stimulus travel through a sensory receptor through the dorsal root ganglion through the dorsal horn and then up the spinal cord through the brainstem to the thalamus and then ultimately end in the somatosensory cortex from there we will send out a motor command in response to this painful stimulus so you'll be aware of the painful stimulus in the somatosensory cortex and then the brain will decide whether to respond to that stimulus so right next to the somatosensory cortex then we'll send information to the primary motor cortex the primary motor cortex will send axons down through the brainstem they will cross over to the other side to control the opposite side of the body because it's contralateral control so if this was the left side of the brain this you think this was the right side of the brain they'd be controlling the left side of the body if this was the left side of the brain it'd be controlling the right side of the body and that information is going to travel through the spinal cord through the descending pathways of the spinal cord and then out the ventral root and then you can respond appropriately for example you may want to walk away from the painful stimulus you're gonna go sit down on a bench to get away from it we also talked about sending information out cranial nerves to say ouch so these will be going to the facial and tongue muscles to seek information out the ventral root would be going to skeletal muscle lower down in the body so that's why I'm saying walk away etc okay so hopefully hopefully you guys at this point have seen enough regions of the brain enough regions of the spinal cord and enough pathways to get a good feeling for how the sensory information comes into the central nervous system where it can be processed through different areas of the brain how then the areas of the brain can send out motor commands to control skeletal muscles and we're going to talk next time about the overall control of the skeletal muscle and the efferent nervous system so not just skeletal muscle but also organs so we will see you in a bit

Channel: Physiology for Students

Views: 148,045

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Keywords: brain, spinal cord, central nervous system, anatomy, physiology

Id: dHURMD4v8Kk

Length: 58min 7sec (3487 seconds)

Published: Tue Jun 14 2016