all right so we're gonna pick up now with our second lecture video in the peripheral nervous system sensory pathways and nerves and when we left off the first lecture video we were just about ready to talk about dermatomes and as I think I mentioned at the end of that first lecture video dermatomes are think about them as regions of the body innervated by specific sensory nerves so just for recap just to kind of remind you what we've seen before sensory nerves carry information from all of these sensory cells out there in in the body at large that information then feeds into the spinal cord via spinal nerves so remember spinal nerves are mixed to a point they contain both sensory and motor function but once we get to the the root of the spinal nerves that's where we start seeing individual functions all right so these neurological impulses these Action potentials arrive at the spinal cord through the spinal nerves and from there into the dorsal nerve Roots so remember the dorsal root of a spinal nerve is the sensory part and the ventral side is the motor part all right as far as the spinal cord is concerned so what happens then is that different regions of the body are innervated by different spinal nerves and so if you suspect for example that a patient has a spinal cord injury what you might do is you would you might assess the functionality of their dermatomes to determine the extent of the injury they have both where it occurred as well as how severe it is okay so we'll we'll look at some pictures that will make a lot more sense once we do that but this is basically a clinical assessment that can be used to determine the extent to which someone has suffered a spinal cord injury um this is all also known as the Asia evaluation so Asia is an acronym that stands for the um American spinal injury Association American spinal injury Association so this again is a way to evaluate a patient for uh damage so these images aren't the greatest at least the ones on the left are not but it shows enough I think to kind of get the idea across we have the brain we have the spinal cord we have cervical thoracic lumbar sacral and spinal nerves that feed into the spinal cord at all of these levels so spinal nerve number one going to thoracic spinal nerve number one going into cervicals found there for one going into Lumbar and so on every time we reach a new region of the spinal cord we reset the numbers of the spinal nerves okay so over here um if we actually you know what let's do this if we zoom in if it lets me zoom in Far Enough we can actually see some of the evaluation that's done with this type of of test so you basically will do a series of motor function both right side and left side to determine the extent to which motor function is is functioning properly in the spinal cord and then we also have a sensory portion where we have light touch or pinprick right side left side different levels and that will also determine or help us determine how well the spinal cord is is uh receiving information from the sensory parts of the body so um specifically um over here on the left with motor function we have five different Neons here we have five different ones here with sensory we can do that for the entire body all right and so what events ends up happening eventually if we look um really hard to see some of these but like if you look uh like here right this portion of the thigh the legs this is uh L2 spinal nerve L2 which is right here and so you could you know do like a pin prick or a light touch test to see if if that information is being received here and processed from the sensory cells in this region of the body okay so that's the idea you can apply these pinpricks you can apply light touch as we'll see later on there are other ways of assessing this as well okay we'll we'll look at cranial nerve assessment as well okay so this is a map of the dermatomes um again it sort of shows you which parts of the body are innervated by which parts of the spinal cord and which spinal nerves as you might imagine C is cervical C is thoracic L islambar and S is sacral just like you'd expect but this shows us where the different regions of the body are sending sensory information thoracic um uh region number six or Seiko region number two or lumbar region number one or whatever right so we can we can assess um the functioning of the spinal cord from there so what happens if for example somebody has a sensory perception at t11 but no sensory perception at T10 so what would that mean about their functioning of the spinal cord it would probably mean that there is some sort of damage between T10 and t11. if 11 is not functioning properly but 10 is that implies that there is some type of interruption of signal happening between T10 and t11 which is preventing information from making that jump to the T10 part of the spinal cord okay we've seen the um homunculus before as well the somatosensory cortex right so part of the um cerebral cortex which is uh involved in the perception conscious perception of stimuli out there in different parts of the body um the primary cementosensory cortex we have and we've seen pictures of this we'll see another one again in a second here is organized somatotopically which means it's organized based on regionality of the body the cortex itself is organized by the different parts of the body that are sending information to the brain um this is going to pertain to Sensations that we are conscious of it does not relate to uh subconscious things like uh blood pH or body temperature or those kinds of things um if you walk into a warm room and you feel that it's warm that's the type of nervous function we're talking about is conscious awareness of sensation wow this room feels warm that would be a somatosensory type um of I guess statement um we also have broadman's areas uh one two and three again we're not going to be responsible for specific areas but I do want to mention those um and then broadman's five and seven are for associative somatosensory areas so um sort of relaying the information in a sensory stimulus to some previous experiment or experience that may have involved a similar kind of stimulus so it's it's associating a particular stimulus with previous exposure to stimuli that produce the same type of result uh a stereo stereognosis a stereognosis um is a situation where you are unable to identify objects by touch so if you were to um so many blindfolded you and handed you a banana there's a really good chance you would be able to like feel your way through that and determine what object you're actually holding if you use take away the banana and give them a football there's a really good chance they're going to be able to you know feel the the shape and the surface features of the football and know more or less probably what it is if someone is suffering from a stereoagnosis then they're unable to identify those objects simply by touch they would have to see them or involve some other kind of of sensory input to identify those particular objects stereognosis okay so here is our homunculus um representing the primary somatosensory cortex so again they're blue wrinkly foldy stuff is dealing with information that we are consciously aware of especially as it pertains to sensory information so as we have seen before as well the larger the body part is on this picture the more sensory cells we have devoted to perceiving sensory stimuli in that part of the body okay so um hands a lot of sensory stimuli lots of sensory receptors so they're going to be relatively large on this um the nose not so much uh so it's going to be a bit smaller right so you get the idea that's that's kind of uh how this works lips um lots of sensory cells that's what allows us to speak and form words and also to chew and detect the tactile nature of the food that we're eating and those kinds of things notice how digestive tract not so much all right so we don't really have a whole lot of um conscious sensory input coming from the GI tract there just aren't sensory cells there at least of this type so we don't really get too much of feedback as far as what our GI tract is doing at any given point in time all right so that's our primary somatosensory cortex once again the size of the body part is representative of how many sensory cells are associated with that body part all right so from there we're going to go into the motor lights and primary tracks okay so we're gonna look at a few of these and these are gonna seem kind of complicated at first but we're gonna walk our way through them I'll give you kind of the tour the rundown and then once we've done that I think you'll be you'll be in good shape all right so we're going to start off um different modalities here different Pathways uh so let's take a look at the um lstt first so lateral spinothalamic tract okay the lstt is primarily involved with the detection and transmission of information relating to pain and temperature as you might expect this is going to involve the nociceptors which are free nerve endings it could also involve kraus's bulb which if you recall is a type of cold receptor so if you've ever had like um uh like your hands especially or your toes get really really cold and then when you start to warm them up they start to hurt that would be krause's bulb doing that producing that sensation for you most likely we also have a ventral spinothalamic tract the stt this one is concerned more so with crude touch pressure in other words and so we have free nerve endings we also have Pakistanian corpuscles they are located out there in the skin to detect those types of stimuli and then we also have a dorsal column medial Le meniscus dcml which is going to help us to perceive and deal with information relating to vibration um two-point touch discrimination means if you take like two pins and put them in two locations on the skin can you actually feel that there are two pins or does it feel just like one pin and so the closer you can bring those pins together and still discriminate them as being just one pin the the greater or the more finer scale um tactile ability you have at that point in time also proprioception here is is also going to play um a role in dcml okay so let's see what they look like um first thing I want to do Point your attention to the top of the slide um spinal thalamic refers to the spine and the thalamus spinothalamic starts in the spinal cord and eventually goes through the thalamus at which point the information is then distributed to the appropriate parts of the brain to process and handle that information so it's gonna look something like this so like I said we're going to go through these and talk about what all these abbreviations are and you'll get a better sense for what we're um what we're dealing with here okay so we're gonna start all the way on the left actually with all these pictures we're gonna start on the left and on the left we have a sensory receptor which is picking up information from the environment like we said on the previous slide this information is going to be primarily relating to pain and temperature because we're dealing with lstt here lateral spinal thalamic tract all right so our sensory receptor is activated by a painful or cold stimulus that is going to eventually the axon from this receptor is going to join up with some peripheral nerve and work its way toward the spinal cord eventually this peripheral nerve is going to join up with a spinal nerve right so we've seen those before as well as spinal nerve which is going to have its cell body or its Soma in the dorsal root ganglion all right so this represents like the Axon of the spinal nerve this is the cell body sorry these are dendrites these are dendrites this is cell body this is axon okay so dendrites cell body axon uh this sends information via the dorsal horn into the spinal cord um we can help a couple turns we'll talk about here in a second and now we have an ascending lateral column of nervous tissue so it's going up the spinal cord but on the sides of the spinal cord okay so that specifically is where this information is being transmitted is laterally or in the sides of the spinal cord as it ascends toward the brain okay um the anterior white commissure is essentially a tract of nervous tissue which runs up and down the spinal cord okay decussation refers to a situation where the signal crosses over to the other side so if you have a signal traveling on the right side that jumps over to the left side we would say it is decasated at that point in time all right so we have our um spinal cord here we're going to feed that into the thalamus which is a part of the brain the thalamus can then send the information on to the appropriate capsule where the information is processed and from there we can now start thinking about sending perhaps motor signals back in the opposite direction all right so that's the first one here's the second one all right so now we have our receptor our peripheral nerve our spinal nerve our dorsal reganglion cell body our dorsal root so everything the same so far but now for this one for the ventral spinothalamic tract now we have a split that occurs we have a backup actually so the ascending Branch feeds into the spinal cord approximately 10 levels up from where it's actually oriented relative to its own spinal nerve so this is a backup for sensory input um we have again the the axon of the spinal nerve feeding into the dorsal side of the spinal cord um it goes up the ventral column now not the door not the lateral but the ventral side now of the spinal cord eventually it reaches the thalamus and from the thalamus goes to the internal capsule okay so that's the same that doesn't change from above either it's the really the main thing here is the decussation that occurs and the Redundant sensory circuit so bottom line here is if you have a sensory stimulus on the right side of the body we're going to feel that as if it's coming from the right side of the body but we also have some signal traveling over to the other side and that's traveling um of the other side of the spinal cord so if the right side were damaged the left side could still provide you some information about sensory input on or into the spinal cord and then our last one dcml this one goes through the dorsal column of the spinal cord eventually through the brain as the medial Le meniscus okay so again starts off the same receptor peripheral nerve spinal nerve dorsal root ganglia dorsal root dorsal horn dorsal column so now we're going up the spinal cord now we reach the medulla from the medulla the information goes to the thalamus the thalamus it goes the internal capsule that's where the sensory information is processed the medullary nuclei um the gracil itates um essentially these deal with the upper half and lower half of the body all right so these are these are going to be medullary nuclei in the medulla oblongata there are groups of cells that are dealing with sensory information either from the upper or lower half of the body so we'll see those as well um all right so let's do this one and we'll wrap up this section uh this is a this is a situation where um it's possible that someone may have experienced um a spinal nerve or actually in this case a cranial nerve injury this is cranial nerve now not spinal nerve but we have a suspected cranial nerve injury um Cradle number five which is a trigeminal ganglion which innervates regions of the face in this case now the information is coming right to left so we have our no I'm sorry this one is left to right as well this is this is sensory over here so this is sensory feeding into the trigeminal ganglion which then goes to the pons from the pawns to the brain stem from the brainstem to the thalamus from Thalamus to the again internal capsule so this one is one again where um it's a fairly similar Pathway to the other ones that we saw but it's also different because this one does not involve spinal nerves it involves cranial nerves which we're going to see in our our third video in this uh in this lecture all right so we're going to skip that slide and we'll pick up with cranial nerves in the next section