this lecture looks at the general and special senses however in particular we are going to focus mostly on these special senses and the reason for that is because we have covered the general census to a pretty solid degree throughout the nervous system and the five chapters that we cover there so the first thing we want to talk about is the difference between sensory information ie stimulus and then a sensation a sensation is what we determined to be conscious awareness of incoming sensory information so basically any stimulus forward should become consciously aware of what you think about consciously that is considered a sensation whereas a stimulus is merely information that has come in through the peripheral nervous system that has been detected by a receptor and it doesn't become a sensation until it actually is you're consciously aware of it and it's dealt with in your cerebral cortex now as always stimuli are still detected by receptors and we talked a great deal about this in the nervous system now there are two classes of senses the first part those general senses temperature pain touch stretch pressure these we've talked about quite a bit more broadly in the nervous system but the ones we really have not talked about other special senses gustation olfaction vision equilibrium and then finally audition now receptors can range in complexity from a single celled dendritic ending of a neuron to a complex sense organs so it can be addenda right dendritic ending of a neuron or it can be something as complex as the eye or the inner ear or the taste buds on the tongue now the idea behind receptors is that they monitor both internal and external conditions and conduct information about the stimuli that they're collecting to the central nervous system and one of the ideas that we want to kind of drive home about receptors is that there's an inverse relationship between the size of the receptive field and our ability to identify the exact location that stimulus came from so if the receptive field is small that means that precise location localization and sensitivity are very easily determined so that is that it the precision is great so if the field is small the precision is great that we can determine exactly where that that sensation care that stimulus came from however when you have a very broad receptive field then you often have only a general ability to determine where that exact stimulus came from so it's a bit more difficult to precisely determine the look the location of the initial stimulus now we have a couple of different sensory receptors and we want to talk a bit about the idea of acclamation so tonic receptors are involved in maintaining our balance they allow us to help keep our head upright so they're the one they're the receptors that if we lean too far back in the chair if we lean too far back at a chair that this that that we feel that sensation that were we're falling backward and then we respond to it by trying to make sure we write ourselves before we fall over phasic receptors are different these are things that purse a signal the increased pressure on our skin so think about the idea of pinching somebody or pinching yourself right that information is taken interphasic receptor and phasic receptors can undergo acclimation which is where we reduce we have an active reduction in the sensitivity to a continually applied stimulus so it's the idea that you can become less and less sensitive to a stimulus as it's becomes more and more frequent because again if it's more and more frequent it's little less likely to become a detriment to our survival or it's easier to ignore there could be a lot of reasons why we acclimate to it when it comes to receptors it depends upon where we find them special sense receptors are housed in those complex organs in the head so the complex complex sense organs whereas general sense receptors are just distributed throughout the skin and organs so there are continuous with a to a great extent with our an idea of the peripheral nervous system and we classify these based upon location of the stimulus or their location on the body external receptors are receptors that are found in the skin and mucous membranes and are open to the outside and these include our special our special senses inteiro receptors these are receptors located within the walls of our viscera and our monitoring sort of the internal environment within our body proprioceptors these are receptors in our skeletal muscles tendons and joint capsules and help us understand our relative position of our limbs and whatnot this stretch in our skeletal muscles the extension and whatnot in our joint capsules we can refer to these by body location as well by thinking about what they do so chemical receptors per se are obviously going to respond to specific molecules and fluid temperature response to temperature changes in temperature it's pain detects damaged tissue touch detects fine or light touches and this is something that you want to make sure you discern from pressure pressure response to mechanical pressure vibration and stretch so pressure and touch are different things I have the the idea of touch I usually like to use when we think of if you've ever had a sibling if you were do this if you ever as a kid messed with one of your siblings and you would they would fall asleep and you would take all the the hairs on their arm on the back of their neck or something that is fine touch that is life touch pressure is when you press on something that's pressure right proprioception and we just talked about changing position position tension stretch of a muscle or joint all right so let's first start talking about taste this is referred to as gustation and we find this entirely on the dorsal surface of the tongue and the gustatory receptors are housed and specialized groupings of cells that we call taste buds and taste buds lie along the sides of epithelial projections that we often refer to as papillae and a year again is this time that we see once again being used the term papillae each bud contains about 40 gustatory cells this works in combination with olfaction and i think all of us understand that from from being sick at one point in our life you had a cold that carried with it a great deal of congestion you would have recognized pretty quickly that that if you can't smell very well with your nose then also you can't really taste very well in your mouth either and so you have that that combinatorial effect there are four specific types of papillae that we're going to cover here the first are called filiform papillae these are found on the anterior 2/3 of the tongue these do not house tastebuds and have no sensory role they're more for friction and for drawing things into the mouth fungiform papillae are primarily primarily on the tip and the sides of the tongue and these contain only a few taste buds each avail eight or sometimes referred to as circumvallate papillae or arranged in an inverted V on the posterior of dorsal surface now the interesting thing about valeted papillae is that they're the least number in terms of papillae there at least numerous in terms of the number of papillae but they have by far the highest number of taste buds purpley and each is surrounded by a deep narrow depression last papilla is going to be the foliate papillae and these extend as ridges on the posterior lateral sides of the tongue now these hounds only a few taste buds during child childhood not well developed overall on the human tongue now there are five basic tastes sensations arguably of the potential for six but we're we're going to cover the five today so they're salty right the the taste that we associate with metal ions this is a salty taste there is sweet taste and this is often that taste that we associate with organic compounds like sugars like glucose there is the sour taste that we associate with acids so this being something of a low pH something less than seven whereas there is a bitter taste this is the taste association with alkaloids and an alkaloid is a molecule like tylenol for example with a pH of 7 or of above 7 and if you ever have a head Tylenol on your you'll I mean for those of you that have had a Tylenol on your tongue that's not coated that pill is extremely bitter and it's often these are very unpleasant taste in your mouth because of that bitterness that's because it's an alkaloid and we often respond to alkaloids as being much more toxic or dangerous umami I love this flavor I love this sensation umami this is sort of that savory flavor that savory taste and this detects amino acids and it's a pleasant taste think of like chicken soup or vegetable broth it's a broth flavor with or a it's often associated with things like that and that's because your dear you were picking up on the amino acids and this in turn is a pleasant taste to the body now there's arguably a sixth taste however this one is not necessary and known for sure yet but that is the taste of water and it's thought that we might be able to taste water in the pharynx but again that is not yet known for sure now olfaction so it's not a sense of smell the receptor cells here are used to detect odors now these are bipolar neurons that synapse with the olfactory bulbs these neural factory bulbs on the actual brains it would be cranial nerves and one these supporting cells are these so so so this is that bipolar neuron that I was talking about and here are the olfactory hairs these are actually receptors here and that the large orange or pink cells between those these are called supporting cells and these are cells that that sort of sandwich these olfactory nerves they help sustain and maintain the receptor so they're there to help provide space and protection and cushion for these very important neurons in Basel cells in the other hand these are kind of spread throughout but you see them here in purple these are stem cells and these are there to replace olfactory epithelium which is this tissue overall when as it turns out you damage it and that does happen from time to time for those of you that I've ever opened the oven and not thought about it and just took a took a smell because something smelled really good but then you forget that the heat the the initial wave of air that's coming out of that oven is going to be incredibly hot and so you burn the inside of your nose that can often initially make smell or harder to detect now the olfactory system in humans is kind of pathetic but we can recognize as many as 50 or 60 different primary odors whereas dogs can distinguish thousands of these different primary orders so ours is more basic or basal level in terms of its abilities the epithelium itself covers the inferior surface of the cribriform plate so here is that cribriform plate from the ethmoid bone everybody's favorite bone and these are the cribriform foramina through which those neurons are passing and that epithelial epithelium in this area here also covers things like the nasal Concha and the nasal septum and the glands within this epithelium secrete a thick pigmented mucous vision is the ability to visually perceive light color and movement so we have visual receptors what we call photoreceptors that allow us to actually discern from these things and there so the visual receptor itself is actually that what allows for the sense of vision but there are plenty of accessory structures on the eye that help the I do its job but are not directly involved in the ability to detect light color and movement so some of these are things like to conjunctiva the conjunctiva is an outer covering on the front of the eye that covers the cornea and a bit of the anterior portion of the sclera so it's that anterior exposed surface now all of us have had some kind of run-in with the conjunctiva we just don't think about it if you've ever had pinkeye pinkeye is also known as conjunctivitis and it's conjunctivitis is an inflammation and infection of the conjunctiva and and by this respect you would often feel that scratchy itchy feeling in the front of the eye and then the overproduction of that almost thick fluid that actually ends up gluing our eye shut if you let it go for too long dad he's kind of characteristic with pinkeye or conjunctivitis the eyebrows eyelashes and eyelids obviously do not allow you to perceive light but yet are not any less important they prevent foreign objects from coming into the eye or coming into contact with the eye they're there to help keep things away obviously the eyebrows and eyelashes are there to help keep say dirt if you have dirt on your forehead or dust in your forehead and you're sweating it helps you helps keep that dirt from flowing down with the sweat into your eye the eyelids there the obviously there to keep it help keep him something from coming into the eye so for example if you're walking into a dust cloud or driving into a dust cloud so you're driving and your windows open and you don't have enough time to actually close your window sometimes you might close one or both eyes to keep the dusty air from getting in there the lacrimal glands the lacrimal glands are there to keep the eyes moist to keep the exposed surface of the eyes moist clean and lubricated so the lacrimal glands are the same glands that allow you to cry and the fluid that they produce has a great deal of dissolving molecules in them that help keep it just generally moist but also help keep it clean help keep it from getting infected and then finally we have the extra ocular muscles and the extraocular muscles are there to actually move the eye so that we can look up or down or left or right or straight ahead just going over this real quick here the conjunctiva is going to line this inner surface here all the way along into the cornea and then back here so that's that conjunctiva eyebrows eyelids obviously in the eyelashes we've covered that material so far now to also make clear some of the other structures that we should find here the cornea is that big dome window that clear dome window in the front here that's the the part of our eye that were most often used to or associate with it the white of our eye that white layer that goes around almost the entirety of our eye - a little small portion in the back and then the area that takes up the cornea is called the sclera that is another tunic of our eye and the sclera and tunic I'm sorry the sclera and the cornea are actually continuous with one another so where the sclera ends here the cornea picks up so that we have a clear window through the front of our eye and then here where this the cornea ends the sclera will again pick back up again the choroid is this layer just deep to the actual sclera and this is a vascular layer so there's actual vascular ssin there's blood flow in this layer and then finally we have the deepest most layer here the actual retina we see the retina here and yellow all the way covering almost the entirety of the eye except for the front of the eye and this little portion of the back here other structures that are up note that will we'll talk about in lab are things like the iris this is that structure here it's often colored or pigmented the space in between the portions of the iris this is the pupil this large structure here that his cross-section is the lens these white ligaments here are the suspensory ligaments this structure here we can see the aura sirata here and we can see the ciliary body so the aura sirata is this posterior most edge it looks like a tooth or serrated margin of the ciliary bodies overall which are this whole margin of structures right here now we look back to the very posterior aspect of the I will see what we call the optic disc and this is the area where there's a gap between this portion of the retina here and this portion of the retina here this gap lacks any photo reception whatsoever and it's considered to be the blind spot so optic disc and blind spot often go hand-in-hand in terms of the name being used and the idea is that it's called the blind spot because there's no photoreceptor and thus no image forms there now here's the interesting thing so this area here is actually the blind spot and this little area here is called the macula lutea called the yellow spot and this area is a depression and it's a rounded yellowish region it's a pit and the pit deep within it is called the fovea centralis and this is the area of sharpest vision on the retina then by sharpest I mean it contains the highest proportion of cones and almost no rods now the cavities and chambers of the eye are a bit confusing so try to follow along with me here just because it's kind of a pain so first I want to take the eye and want to put it up and do it's two cavities and so we see that associated with the actual lens so here's that lens again it's a cross-sectional lens so this anterior surface of the lens all the way forward to the posterior aspect of the cornea here this area from here to here is considered to be the anterior cavity and the posterior cavity is from the posterior surface of the actual lens all the way back to the anterior surface of the retina and in the anterior cavity is a fluid that we call the aqueous humor this is a very liquid based filling fluid that occupies these areas and in the posterior cavity this fluid that is within this chamber is actually living in this cavity I should say is actually much more like a stiff jelly and it's called the vitreous humor now so let's break down the anterior cavity a little bit more into its two separate chambers because the anterior cavity has actually two legitimately different spaces from the front or that is the anterior surface of the web's to the posterior surface of the iris here this is called the posterior chamber and then from the anterior surface of the actual iris here to the posterior surface of the cornea this is now the anterior chamber so we've got two chambers within the anterior cavity the posterior cavity however is just that it's just the posterior cavity no chambers within it now the humor I'll talk about these two because they are different the vitreous humor is very thick it's very gelatinous it's there to help the eye maintain its shape and that again is seen in the posterior cavity the aqueous humor however this is aqua water fluid so it's a little very much the same consensus the consistency of water and this is meant to flush waste products and remove them from the eye it's very fluid as a result the aqueous humor is secreted into the posterior chamber it flows around the lens through the pupil and into the anterior chamber so it's going to flow in this direction and then it's going to flow outward these structures here called the canal of schlemm this is the old term canals of schlemm one of my favorite terms ever in anatomy is the canals of schlemm now they're called the scleral venous sinuses but before they were called the canal of schlemm either way it's small sinuses on the either their help meant to remove fluid from the eye and allows drain now as we talked about before when it comes visual pathways we see decussation that exists in both both eye so both the left eye and the right eye whereby information from the left eye goes to both the left and the right hemisphere and vice versa with the right eye now at the optic chiasm some of those axons are actually going decayed and you see that here left eye being all blue axons some go to the right some go to the left and same thing with the right they're all in red red axons some are going to go to the left so we're going to go to the right so in essence the optic tract which is either here or here contains axons from both eyes and visual stimuli is going to be processed by the hypothalamus and then interpreted by the visual Association areas of the cerebrum we see those back here at the occipital lobes hearing equilibrium so we're gonna move past the eye now and into our ability to hear that's audition and then I equilibrium which our ability to maintain balance and know where we are in the world in terms of we have set down right set up or whatnot compared to the way we're supposed to be now the external ear itself is this area here and this is largely just meant to be a funnel this is located mostly outside the body and the middle and interior is middle here and then the inner here are housed within the petrous portion of the temporal bone so for those who neither remember the petrous portion of the temporal bone that is in fact the middle and inner ear now sound is meant to be collected here by the oracle and then funneled through the external auditory canal onto the actual temp Anik membrane and the idea here is to convert these sound waves into mechanical movement and this whole system is based upon movements in the inner ear fluid so sound waves will come in this direction so through the external auditory canal though vibrate the actual tympanic membrane which will in turn vibrate each of the three your inner ear ossicles right here we have the Mei leus the incus and then finally the stay piece that is attached to the inner ear and that will then register movements those vibrations will then in turn register through the actual inner ear and the changes to the fluid inside the chambers within that inner ear are actually what is then sent off to the brain for interpretation so those are the sensations okay to go through these things again the external auditory canal or me Attis is this region right here the Oracle is the overall ear I'm the flap on the outside of the skull right here that that soft tissue portion of the ear that we often think of being the ear now we have a helix and an anti helix heat-ray it's an anti tragus none of which i've seen really great here you'll see them much better on the models and lab the tympanic membrane i've referred to already once or twice is this white membrane here that is meant to register those sound waves coming through the external auditory canal and the function of this system overall is to funnel sounds in this direction the middle ear contains an air-filled tympanic cavity so this whole area here is all filled with air which is why we feel such changes in pressure and an airplane as we're climbing an altitude now you've got a bony wall all the way around this structure here almost all the way around but we do maintain an open passage where an open connection to the atmosphere through the auditory tube which connects to the pharynx here nasal pharynx specifically and we call this the auditory tube with the eustachian tube and so the reason why you can drink fluids or chew swallow during ascending in atmosphere within a plane and help regulate that pressure in your ear and make your ears pop is because of this open passageway here the auditory tube right here now the middle ear is what houses the auditory ossicles the mailee is here the incus here and then finally the stay piece here now that your station tube is that open connection into the nasal Frank's that we see all the way here and it's that air fluent air air movement through this tube that results from the following movements that allows pressure to equalize on both sides of the tympanic membrane so that way when we increase in altitude the pressure doesn't actually burst or tympanic membrane now within the inner ear there's a lot of structures here not all of them were going to cover all that particularly well or in any kind of detail what I do want you to recognize it that that all these passageways in here are actually right here are actually fluid filled chambers or tubes and we've got a couple of different labyrinths within this system we've got the membranous labyrinth here you can see it's surrounded by a pink membrane and within that we've got a fluid that we call the endolymph and then you've got all these blue lymph areas and the actual spaces within them and these are called the bony labyrinth and the blue fluid within them is actually called perryland the major area where initially sound comes into or so I should say vibrations come into you is called the vestibule and this information is then going to pass pass into the actual cochlea we see here for interpretation the semicircular canals here here and here are kind of a three-dimensional axis and they allow us to deal with equilibrium so this is that equilibrium system for the special senses and the idea that I want you to keep track of is that if you look here in this slide you see these purple extensions of a cell that we call the hair cell they're sticking out into the fluid and we noticed that when the woman has her head upright like this like any of us would the fluid is held in a certain position and thereby so are the actual hair cells and this is interpreted by the body as a upright head whereas when she tilts her head forward or downward I should say then gravity takes hold of this fluid and pulls the fluid downward and thereby we see a response by the hair cells in kind these hair cells actually begin to fold forward as well and that response the this stimulus is going to be interpreted by our brain as our body or our head tilting downward and forward and we have to do something about that potentially now equilibrium just as we're talking about here is rotation of the head that causes the endolymph within the circular canals to push against a structure we call the cupola which is covering the hair cells and so this is that this is that cubular and when it moves the hair salesmen and when the hair cells move this in turn that registers is a certain stimulus to the actual brain