for part two of this introduction lecture we will now transition to a discussion a brief discussion of the special senses so as you might recall from past exposures uh the cerebral cortex is made up of four different loes and going from anterior or front to posterior and back we have frontal which is in front par Bridal which is up temporal which is off to the sides or near the temples and occipital is Outback so let's talk about the primary sensory processing that occurs in each of these respective cerebral loes okay so for smell and taste these are located deep within the frontal lobe and as you can see the olfactory cortex is more anterior to align with an important structure that is important for smell processing the olfactory bulb uh which is located very close to the olfactory cortex the gustatory cortex is uh located deep within the frontal Globe again to align with the anatomy of the T and the cranial nerves that attach to the tongue so now we move on to the temporal lob so as you could see the primary auditory cortex is located in the temporal lobe and as the name suggests very important for auditory or hearing processing um and again gustatory refers to taste with old factory referring to smell now when we move to the par vital lobe we have the primary somat sensory cortex which is important for touch processing and we have the occipital lobe which is very important for primary visual processing so please do keep in mind that these primary centers are really more focused on sensory processing which is um related to you know processing based on our experience with a world that is not necessarily reflex oriented so in some instances especially for example with visual processing we will see that the reflex pathway for visual processing takes a different route compared with the longer route of primary processing of visual information from the sensory world so why might that make sense well if something is about to hit your eye you need to be able to close your eyes very quickly but in order to understand or evaluate a scene of view you really need to take your time and process that information so now let's make sure we understand what a stimulus is so a stimulus is formally defined as an external substance or energy an odorant a scent a sound pressure wave these are some examples of various stimuli or a stimulus can be something that is internal an emotional memory that produces a consequential motor or behavioral response so when we talk about sensory systems an external stimulus must be received by a structure called a receptor and then converted or transduced to electrochemical information so there are specialized cells within sensors with sensors excuse me that are known as receptors which receive and begin to process some of the properties of the sensory stimulus information for example different regions of our skin can contain mechano receptors meaning that they respond to pressure um for touch stimuli and again each of our sensory systems has unique sensory receptors right um and again unfortunately for the time limits of this course we don't get much into the discussions of The receptors um but you know there are opportunities that we may have in other coursework each type of sensory stimulus whether it's a tactile or touch stimulus for example gets converted from its original form for example for touch that would be mechanical pressure to an electrochemical signal this is known as transduction when you transue something you're changing it from one energy form to another so here basically what we're saying is that different sensory information from the external world is coming to us at all of these different energy forms but our brain doesn't talk with those energy forms or communicate with those energy forms so those get transduced or converted to electrochemical signals the way that our nervous system likes to talk or communicate reflexes versus instincts so a reflex is an involuntary meaning that you don't control it Auto automatic response to promote survival most reflexes are controlled by the spinal cord or cranial nerves that connect to the brain stem therefore they don't require processing of the cerebral cortex or past experience and there is little communication to the Brain before a reflex action occurs so lifting your finger off the hot stove you know that's really happening at the level of the spinal cord you don't need your primary somata sensory cortex involved in that however an instinct is a learned response to promote survival instincts require significant processing of past experiences by the lyic system and prefrontal cortex so here for example an instinct is automatically to position your body far away from your George Foreman Grill um as soon as you're beginning cooking because you know you have past experience ooh when I got too close I got burned that is not a good feeling so you know you also remember over time well let me just stand back from here so important philosophers and scientists associated with the study of reflexes include Renee deart and Charles sharington so a reflex arc or a defined pathway of reflex-based actions involves a stimulus a receptor or sensor the connecting sensory neuron which then either follows a spinal reflex arc with something called an interneuron in between to connect the sensory neuron with the appropriate motor neuron which connects to the affector muscle to lead to the response so for nonreflex actions we have the sensory neuron connecting to the cerebral cortex the appropriate uh Pathway to get to the primary sensory cortex which then communicates with the prefrontal cortex for conscious decision making then communicating with the primary motor cortex to then communicate with the lower motor neur uh excuse me first with the upper motor neuron then with the lower motor neuron to lead to the fector response okay so this first part over here is all related to reflex and this part over here is related to conscious decision-making thoughts which may also include instincts contralateral so when you hear this word you want to think of the prefix contra being like contrasting so cont Lateral with lateral meaning off to the side refers to sensory processing that occurs on the contrasting or opposite side of the central nervous processing system so that means H if I touch something with my left hand that means the right hemisphere of the brain the right somata sensory cortex is going to be processing it and hm if I touch something with my right hand the left hemisphere your somata sensory cortex is going to be processing that information so most sensory motor processing is primarily considered controlateral with key exceptions right so there's always exceptions and it's always important to have more than one Pathway to promote survival in the event of injury right so we want to keep all those things in mind however the way that our bodies were anatomically developed they developed in such a way that it made sense to have primary contralateral processing so ipsilateral ipsilateral refers to the sensory processing occurring on the same side of the nervous system okay so for example certain proprioception so our awareness of our body relative to internal space without you know visual inputs that is proprioception right so um that is a sense that is processed in an ipsilateral manner it is very related to our ability to maintain balance so instead of having these complex connections with this uh cerebral cortex it has a ipsilateral or same side processing to the cerebellum of the brain a little bit different pathway there so now when we start talking about you know Paths of information flow in the brain you may very well come across these terms aarant and eent an aarant pathway is moving away from something right so you're starting somewhere and you're moving away whereas an e e faren pathway is moving toward something in other words it's preparing to exert an effect now let's describe ascending and descending so ascending which we usually think of as going up and that's correct but in biopsychology it's very important for us to carefully distinguish ascending versus descending Pathways so the most basic starting point for an ascending path way is the sensory receptor or brain stem working up to the prefrontal cortex the highest brain center right so the most basic brain Center is the brain stem and then we work up to the highest point the top the Apex the prefrontal cortex so globally sensory processing pathways are largely considered ascending you're moving up that information descending descending means to go down and in biopsychology and learning we talk about descending brain Pathways the most basic starting point for a descending brain pathway is from the prefrontal cortex or the highest brain Center down to the final response output so the brain's evaluation and motor actions in response to sensory signals are referred to as descending so here in this context uh we're not going to get too much really involved in the kind of sub distinctions of ascending and descending this is the um the extent that you need to understand ascending and descending um but you know in more advanced courses we will have some further distinctions so here in this figure where is it the information coming from so that would really relate to sensory information and what should move that would relate to motor action so what you really see here in this figure is really and again we will review brain anatomy in more detail but for right now you should recognize this blue region over here this motor cortex is basically sliced out and presented right over here and uh also the somat sensory cortex which is right over here is basically sliced out and presented over here okay so what divides the motor cortex from the somato sensory cortex the central sulcus so the frontal cortex contains the motor cortex and what whenever we think motor we think movement right and when we think somato sensory sensation of the body we think touch sensation right and again you know we'll get into all of the different names for these structures in some detail um you know over time but what I want everyone to recognize is that the both the primary motor cortex and the primary somata sensory cortex are really organized as a sensory or motor homunculus a map that really kind of designates different body sites and what you really should be noticing is that the face regions are going to have more motor cortex and somatic sensory cortex respectively devoted to processing information from the external world that is being sensed by the face and the motor output that is important for the face right so and if we think about it that makes sense because our face our lips our tongues our eyes um you know and nose are really interacting with the external World in such a um you know extensive way right and so it makes sense that you know a large proportion of those respective brain regions would be devoted to processing sensory or mortar information for the face so now what I would like to do is just give you a brief overview of the major sensory systems so again this course is not really focused on sensation and perception but this is just to give you an overall awareness of um some of the primary sensory system systems so what you see over here is you want to really play close attention to this figure so this figure over here and this figure over here are showing the respective areas of the path but the idea is is that when we have an odorant from the external world right so those odorants come in contact with the olfactory receptors connected to to the olfactory nerve okay and this is connected to the olfactory bulb which is the primary structure that connects along the olfactory tract as it's moving towards the brain and the olfactory bulb Targets in a flat way like these four major regions so what is unique about the olfactory bulb and olfactory processing or smell processing is that unlike other sensory processing there isn't this primary directed path directly to the thalamus as like for other types of sensory processing so why might that be well if you think about Al faction or smell processing and how it developed evolutionarily right well you know most basic species they rely on old factory processing to navigate the external world to maximize their survival much more than humans do and again when we think about the development of our old factory system based on an evolutionary perspective this would kind of align with that reasoning okay so now these olfactory bulb targets the purform cortex olfactory tubercle amydala and ENT rinal cortex are really kind of the basic structures involved in identifying this particular odorant right so our our ability to properly understand what odorant we are experiencing uh the amydala kind of processing the emotional context that is relevant for the presence of that particular odorant and the entor rinal cortex kind of linking um the the memory of what that odor is and what the emotional context is however that being said as our brain evolutionarily developed later on we also have these very important connections of the old factory bulb targets with some other key brain structures okay so let's talk about some of those key brain structures um so the ENT rinal cortex and the hippocampal formation really kind of align closely together in the human brain especially for memory and so it makes sense that the endoral cortex would have some connections with the hipocampal for ration for olfactory based memories so now it's also important to note that the pform cortex has connections with the orbital frontal cortex to really help us understand the honic value or the desirable value of whatever we're smelling right and important to note that the amydala has key connections with the hypothalamus and Thalamus to really kind of then further evaluate the processing of the different odorant and kind of um you know dictate and influence kind of responses okay so now let's move on to the study of the human taste system so when we talk about taste we talk about gustation right so it's important to note that the sense of taste is heavily influenced by the sense of Al faction but again for the scope of our work here we're just talking about the basic Pathways and again um some of those more elaborate topics are discussed in more advanced courses but let's talk about the primary Pathways um that really are focused on processing taste so as you can see there are um taste buds on the tongue and the taste buds on the tongue connect with different cranial nerves so as you can see the pallet and the anterior 2/3 of the tongue connect with cranial nerve 7 which is formally known as the facial nerve okay so taste buds on on the posterior third of the tongue are connecting with the cranial nerve nine which is the glosso Fingal nerve okay and taste buds on the fairings and the upper esophagus are really connecting with cranial nerve 10 which is the vagus nerve okay so um now what I want everyone to see is that the cranial nerve MMS they connect via their respective ganglia to the nucleus of the solitary tract okay and the nucleus of the solitary tract connects to the thalamus which is a major sensory processing center but the nucleus of the solitary tract also directly connects to the H hypothalamus and the amygdala okay and the amydala and frontal gustatory cortices the primary um you know region where taste is processed has important directional connections with the amydala so why might this be important well you know again as we were talking um you know when we want to promote survival sometimes people might taste and ingest or intake a dangerous substance and if you you know eat something that is poisonous right you don't want to wait for extensive processing by the thalamus before you have the consequential response of a gag reflex right so there is some preliminary processing independent of the thalamus to kind of directly pres protect your survival with um you know having some taste processing be independent of the thalamus right but it is very important that you know um the insular and frontal gustatory cortices in their communication with the amydala influence our disgust response when we eat something that tastes horrible right okay so now we're going to move on to the very basics of a tactile sensory pathway so what I want everyone to recognize is that there are many many pads from the spinal cord to the brain for touchbased sensory processing but we are primarily going to focus on the dorsal column system this is the primary processing path for fine touch and some proprio Sensations uh from the body okay so you know there is also the spinothalamic tract which is really focused on on pain and temperature Sensations from the body but when we talk about the dorsal column system okay dorsal refers to the backside so when we are talking at the level of the spinal cord the dorsal side or back side is very sensory focused the ventral side or belly side is more motor out output focused anatomically speaking okay so now that we established we're in the dorsal column system we're really focused on touchbased processing let's talk about the path of information flow from the spinal cord to the brain okay so what we're doing is at the level of the spinal cord we're saying H you know the sensors The receptors receive CE the sensory information and sent it to the dorsal root gangli of the spinal cord okay that information is going to travel along these two tracks and so I don't expect you to memorize these particular two tracks but I do want you to recognize that these two tracks really are representing information that is originating from the lower body for the gillus and the ER body for the catus okay so as you can see here it's traveling along these two paths and you can see here at the level of the brain region of the Medela so we started out in the spinal cord and uh from the dorsal root ganglia we end up in the medulla region of the brain okay so this is called called our first order neuron because it started out in the spinal cord the dorsal root ganglia and it's synapsing with the Medela right neuron number one so now we move on to the next neuron that synapses this is known as the second order neuron so from the medala we have this situation that occurs that now we're crossing over sides okay okay so now we're crossing over sides and then we're moving up the midbrain region all the way until our second order neuron reaches the thalamus okay whoa now the thalamus is a major Center for sensory information processing so now we definitely have to have another neuron a third order neuron synapse over here and send information from the thalamus to that primary somato sensory cortex and which its other name is known as post Central gyrus okay so for the purposes of our course I will just ask that you focus on the dorsal column system you don't have to worry so much about the spinothalamic tract okay so now let's move on to the auditory path way okay so before I get to this kind of summary path let's go through the figure in a little bit of detail okay so here we start out at the level of information from the ear traveling along the auditory nerve okay and we see then it goes to the clear nucleus and then it hits the superior olary nucleus right and so what these distinctions are just illustrating is that we have to process information from both ears right okay so now after the information flows from the superior olivary nucleus we have to move on to the inferior calculus so the inferior culus is a very important structure in the midbrain that is involved in the reflex actions uh especially auditory startle right so from the inferior calculus we have the information arriving to the medial geniculate nucleus of the thalamus okay so the thalamus again is a very important sensory processing structure so the thalamus has a lot of different substructures when you see medial that means it's more auditory focused region lateral means it's more visual focused I'm not going to expect you to remember the medial versus lateral distinction right now okay so so from the medial geniculate nucleus we then have neurons that synapse to then send this information to the primary auditory cortex right so as you can see here we have the different synapsing neurons at each particular location but when we talk about just the brain structures alone when we talk about the path we say auditory nerve to ponds ponds to midbrain midbrain to Thalamus and Thalamus to Cor Vortex okay now let's move on to the visual pathway so the visual pathway has a little bit more involved um kind of processing um and I just want everyone to kind of follow with me carefully so in order to really not get lost with visual processing it is very important to keep track of these color designations and keep track of the concept that what appears on the back of our eye which is known as the retina is upside down and inverted from what we see in the real world okay so what does that mean so whatever we see on the left side of the world which is shown in red for each of these eyes eyes is going to end up on the back and right side of each respective eye so whatever we see on the right side of the world which is shown in blue is going to end up on the um backa that is to the left of the retina okay so as you can see when we're starting out at the level of the back of the eye we are taking information from both fields of view what do I mean by field of view when we look out into the world straight again what's to our left is the left field of view and what's to our right is the right field of view right so you can see at the level of the eye the retina that's already kind of crossed over right so now when the information is leaving the eye it is going to follow along a tra optic nerve okay and it's going to travel along the same direction as it started from the retina not from the field of view right so from the retina it's following the exact same path right and then what is very important to recognize is that the optic nerve hits a point called the optic kaym so this is a crossover Point okay so now as we originally observed right so both the left eye and the right eye are obtaining information from the right field of view but what you can see here what happens is at the level of the optic kaym all of the information from the right field of view is now going to travel along the left optic tract to then end up at the left visual cortex eventually okay and vice versa everything from the left field of view at the point of the optic kaym is going to cross over to the right optic tract and respectively end up at the right visual cortex so when we're talking about primary visual processing right before the optic tract reaches the visual cortex there's the lateral geniculate nucleus that region of the thalamus important for visual processing and then we have these structures that you know kind of come out called optic radiations that are then going to send it forward to the primary visual cortex all the way back here okay this is how primary information is processed but when we have a reflex action we don't have to travel all that far we just just travel on a more direct path across the optic kaym to directly into the midbrain here right so instead of going all this way like this and like this we just start out like this this and then come down a little bit over here and have a processing there so the figure illustrates key areas for visual field alterations assoc associated with octop nerve or kaym damage so the idea here is that why is it important to study these different types of sensory Pathways and there's many many reasons to study the sensory Pathways right but here I'm just highlighting an example of well you know some forms of um anopia which mean blindness um are really due to um you know lesion of different areas along this pathway and that doesn't mean that every form of blindness is due to this but there are many forms of blindness that can occur as a consequence of damage along this pathway right so it's of Great Value to try to understand you know what's going on okay so as you can see over here figure number one is showing total blindness of the right eye because this optic nerve was completely damaged right so this is the right eye this is the left eye right and so it's also important to understand these words nasal and temporal so when people talk about the nasal side they're talking about the part of the eye that's closest to the nose when they're talking about the temporal side they're talking about the side that's closer to the temporal loes near the forehead so now let's take a look at what happens when you kind of hit that crossover point over here so when you directly hit that optic kaym that's situation number three but let's just look at Situation Number Two where you're just kind of doing a partial leion so remember that the right eye and the left eye the information that hits the retina is crossed over right so when we have that information flowing straight down like this it's coming from the left field of view so it makes sense that if you Legion number two you're going to have um the right nasal hemianopia where this area is blind the left field of view right okay very good so now let's move on to situation number three so here the entire optic ASM is getting damaged right so here we have what is called a bipolar Hemi anopia because you have this midline lesion right and so if we think about the information that is following along this track right so we have you know over here information um for the left field of view from this eye and then over here information um you know coming along and impacting the right field of view so again you know hence the you know um bipolar Hemi anopia so now what happens at the level of number four right so as we know from the previous slide we had complete crossover of the field of view right so that means if you Legion all of number four that is all related to the left field of view right so as that such that makes sense that here when you leion number four the left field of view for both eyes is you know having the blindness which is known as left homonymous Hemi anopia right meaning both left same side field of view right so then let's look at what happens when you leion parts of these optic radiations or the full optic radiation so because the optic tract is then later leading to the full optic radiations if you leion all of the optic radiations it's going to look very similar to number four when you leion the optic tract so that's why number four and number seven lead to the same final result which makes sense but let's take a look at what happens when you leion number five the upper Optic radiations versus number six the lower optic radiations so remember the information from the external world is coming um you know in the opposite direction upside down and inverted um which is then reversed by the brain so it makes sense that when you lesion area number five that you're going to have a you know quadrant Opia one quadrant that is below that is blind right cuz whatever is on top here is going to influence the bottom field of view and here number six which is the bottom optic radiation is going to impact the top field of view okay so now I want to move on to a brief discussion of you know motor processing so when we talk about motor processing in general there are two major processing tracks so the primary processing tract is called the pamal tract so that is really connecting with the primary motor cortex okay and that's where our focus is going to lie so when you also have other tracks that are outside of the primary motor track extra means outside so when you think of the extra parameter tracks you know that they're not focused on the primary motor cortex they're originating from other brain regions that are very important for other actions such as reflex and balance and so on okay so again our focus is going to be centered around the paramal or primary motor tract okay so as you can see here the numbers here 1 2 3 4 represent the motor cortex midbrain Medela and spinal cord and we can see 1 2 3 4 respectively over here so this particular tract is called the corticospinal tract because of um you know how it originates okay and we're going to see this particular primary uh paramal tract in great detail or some detail so now this is the more detailed view of the cortical spinal tract okay and so what you see up here is the primary motor cortex so remember this motor homunculus which shows who there's a lot of pro processing over here so the information from the primary motor cortex okay is going to you know um follow major tracks okay and as you can see here there is the cortical spinal tract and the cortical bu uh bulber tract and so these tracks are really carrying the information that is coming from the face and also the information that's uh going or actually going to be directing the face movements and information that's going to be directing the extremity or you know uh limb movements okay so once the information is you know traveling we see that it's going to you know go through the midbrain and through the cerebral peduncles to and and again this is a processing tract to the Medela and in the Medela there are pyramids and there is a process called decoation that just means that this information is going to cross over from one side of the body to the other side of the body the um you know if we're starting over here um at the left m cortex right at the level of the pyramids then we're going to cross over to the right side of the body okay and then move along the lateral corticospinal tract right um to then lead to the skeletal muscles where we have the affectors the muscles that will produce the response okay and as you can see here you have for the cortical bulber tract you're going to directly move to the skeletal muscles for the facial movement so the bulber tract is focused on the facial muscle movement whereas the cortical spinal tract is focused on the extremity movement okay but I just want you to see the sequence of how this information moves right so as you can imagine with the cortical bulber tract you don't have to go down through all of this process to get you know to the muscles right right so you go along the cortical you know bul or tract and then connect you know via different kind of cranial nerves to the respective muscles of the face okay however it is important to note at the crossover points right so we have pre crossover the neuron that is originating from the primary motor cortex the upper motor neuron that's the first neuron okay so from the primary cor cortex to the pyramids we call that the upper motor neuron okay so from the pyramids to the spinal cord that is the lower motor neuron okay so this particular figure is showing the topographic map movement in the primary motor CeX but here I want us to take a look and see that we have you know the designation of the cortical spinal tract and the cortical bulber tract right so it makes sense that topographically we keep all of the cortical spinal tract you know processing on one side of the Hocus and the face on the other side of the homunculus so this particular figure is an integration um in the control of movement right and and notably let's talk about how sensory inputs are really important um you know especially before a movement is generated but sometimes when we talk at the level of spinal cord and brain stem circuits the sensory inputs really might be more involved in producing a reflex response so at the level of a reflex response we really focus on the spinal cord and brain St as described here and we really wouldn't involve a lot of these upper systems that are involved in more conscious directed movement right so here where it says local circuit neurons so this is really kind of sensory motor integration um and just you know producing a pattern and then the motor neuron pools are the lower motor neurons and again this kind of path is really more aligned with a reflex arc okay however um there is also the upper motor neurons and the descending system that we described that is more complex in terms of planning initiating and directing voluntary movements right so that primary motor cortex is really involved in all of those functions and the premotor region that's directly anterior to that is going to be involved in the memory of executing planning initiating voluntary movements so the brain stem centers are really more focused on postural control and gain adjustments and balance so um you know because of those important connections there okay so now we see that there are two key brain regions that are providing significant input to the motor primary mortar cortex brain stem path and that's the basil ganglia and and so um uh although the name implies that it's outside of the central nervous system the basil ganglia is a sub region of the brain so that's a bit of a misnomer um but the basil ganglia is a structure that is important for the initiation of intended movement and suppression of unwanted movement okay and so this provides significant input to the motor cortex the cerebellum has an important role for coord ation of ongoing movement and um you know when we think about the brain development so some basic motor learning and motor memory is very um influenced by the cerebellum especially when we talk about things at the level of like classical conditioning um just because historically like our brain cerebellum developed before our primary motor cortex okay um and then you know with all of these these inputs the descending system the motor cortex can then send signals to the motor neuron pools to the lower motor neurons right so remember all of this is upper motor neuron and then here the lower motor neurons are going to connect to the affectors which are the skeletal muscles so now let's move on to this figure which is now taking this sensor motor integration a step further and saying H you know what when we really are involved in the control of movement you know we have what we talked about um with everything of this descending system but in addition to that we have a lot of important sensory information that is really being processed by the visual cortex the visual guidance of movement the entoron Ral cortex which is very important for spatial navigation um and the parial cortex um which is the superior parietal lobu and the post Central gyrus right so the post Central gyus being this important for those mechanos sensory signals right those Sensations and the integration of visual and proprioceptive signals is an important function of the superior parial lobules so really understanding our internal awareness and linking it with the visual awareness of where we are in space is really critical for Effective movement as we might imagine right and then we get our awareness feedback of the external World from muscle spindles and GGI tendon organs so again this figure is just integrating that sensor uh additional sensory components that really influence uh motion um as previously described