Welcome to Lab 11, Sensory Organs. This is the last lab of the semester, congratulations, you've made it. Um, there's a few new concepts here that we're going to talk about when we talk about how we actually discuss sensory organs. But this is part two of our exploration of the nervous system. So there isn't too much new concepts, too much new information. Um, we're going to talk a little bit about cranial nerves again, we'll talk a little bit about the forming of the skull. So a lot of these structures are going to be familiar, um, obviously a lot of the brain structures are going to be very fresh in your brain. So, cool, here we go. And we also as- we also have an eyeball dissection this week, which is a very cool one, so great. So before we get started, let's talk about how we study sensory organs. All of your sensory organs are going to have each of the following: They're going to have a sensate molecule, or a force, or something that they respond to. They're going to have a receptor, meaning that they're going to have a peripheral nerve responsible for reacting to that sensate molecule. And then they're going to have a cortex of the brain associated with processing that. So, for each of these systems, here's what we expect you to know. What type of reception we're talking about, whether that be photo reception, mechano reception, uh, et cetera, et cetera. What type of major structures are involved, what sensory organs are involved um, and then be able to trace the signal from the sensory organ, from the actual receptor itself, to the part of the brain where that information is going to be processed. So learn the pathway is the big concept here. Learn what is going um, learn how this starts, where it starts and where it ends. So it's also worth mentioning that this is not a comprehensive list. Your body has other senses, you can, to a degree, sense barrow reception, so, response to pressure. You have proprioception, which is your body's sense of where it is in space. Um, and so we lump some of those in with other ones and we don't talk about all of them. So don't think about this as being a comprehensive list. So, cool. Our first sense of the day is going to be olfaction. Olfaction is the ability to smell, it is a type of chemoreception. Here are some of the major structures that are involved in it. The one I want to draw attention to is the thalamus, because as we talked about last week, that's one of your main sensory integration centers. And so it's going to be important for almost all of these. So, here's an image we've seen before. This is anterior to posterior the interior of the skull. That structure right there is going to be the cranial nerve responsible for your sense of smell. That is obviously your olfactory nerve. And that's going to be the olfactory bulb. That cribriform plate is a label from a few weeks ago. That is going to be um, part of the ethmoid bone. So that's one of the bones of the inner skull that we talked about. Cribriform plate of the ethmoid bone is going to be where the olfactory nerves descend from the olfactory bulb. And now let's show you that from the side. Once again, olfactory bulb, cribriform plate, olfactory nerves and they are going to uh, terminate in the nasal mucosa. So, that's how you smell in your nose. Um, olfaction is going to be processed in uh, various regions of the brain. We've talked about its connection to the Limbic System in the past. Once again, just because those structures run so close to the Limbic System, they're going to have a little bit of, I don't want to say cross talk, but they're going to uh, affect each other quite greatly. So here's how this information is going to be processed in the brain itself. Um, it is going to start in the olfactory nerve. It is going to go through the thalamus which is highlighted. Um, it is going to be processed in the caudate nucleus and the globus polytus, and then it's going to be sent to the temporal lobe. Next up, we have a type of chemoreception which is very closely related to olfaction and that is gustation. Key difference between olfaction and gustation, as we'll talk about, is that for the olfactory system to function, the sensate molecule, or the chemical that you are actually smelling, has to be dissolved within the air. It has to be aerosolized. In order for gustation to occur, it has to be dissolved in fluid, which is uh, why we have saliva, right, saliva breaks down the fluid, and then once it is solubilized, that's when we can actually taste it. And we'll show you why that is in just a second. But here we have our diagram of the tongue. We have a superior and a lateral view. Uh, the tongue has a sulcus terminus in the back. This is going to- um, you know, that term, sulcus should be familiar from our discussion of the brain last week, but a sulcus is like a, a divot or like a depression. We also have the apex, that is the head of your tongue. We also have the body, um so general landmarking terms. But then we have these structures right here. These are your circumvallate papillae, they're going to hold some of your um, some of your taste buds. Then we have your fungiform and filiform papillae, which are going to be on the body of the tongue. Those are also going to house taste buds. Then we have your foliate papillae, which are going to be on the side. And as we'll see here, come on, there we go. As we see here, each of those different types of papillae are going to hold taste buds, which respond to different types of taste. And that's why you can get this map of your tongue where different regions correspond to different tastes. So, circumvallate papillae are going to be in the back, they're going to be responsible for bitterness. Um, and fungiform papillae are going to be responsible for umami, sweet and salty, and then- salty. And then uh, foliate papillae are going to be responsible for sour. I also want to show you very quick um, just that diagram on the right. Your sensory nerve fibers and your basal cells are going to be the site where the actual uh, synapses are. You also have support cells which are going to assist in taste, and that's why these are going to be able to taste different molecules. Um, that's also why these are buds as opposed to just nerves by themselves. So, hopefully that makes sense. You have these gustatory hairs that are going to reach out and are going to react to very very specific molecules. And that's why you can taste uh, very specific things. Cool. So, the signal transduction, I'm going to keep this very simple. It's the nerve fibers at the taste buds, then the cranial nerves associated with the tongue. That's the facial, the glossopharyngeal and the vagus uh, glossopharyngeal, makes sense, right? Um, I know that we've talked about the, the facial and the vagus before, but I'll throw that one in, draw special attention to it. That information is routed through the brain stem and then it is uh, finally prote- finally processed in the gustatory cortex. [Silence] Alright, now let's move on to one of the two biggest systems that we're going to talk about this week, that being the auditory system. The auditory system is the first type that we're going to talk about that is not a uh, chemoreceptor, this is a mechanoreceptor. Uh, and by recan- excuse me, by mechanoreceptor, what I mean is that it is going to be dependent on the action of a physical force. In this case the deformation of hair cells in the cochlea by changes in pressure caused by a signal transduction pathway that we'll show you in just a sec. Also associated with it is the vestibular system, which um, is your ability to orient yourself in 3D space. And yeah, let's jump in. So sound, by the way, before we get started is the um, change in pressure over time. It can be described with amplitude, length, and frequency. Um, we don't necessarily talk about the physics of it in this class, but hopefully these are things that are familiar to you. So cool. Here we have the frontal view of the skull. Here we can see the organs of the inner ear. Now let's zoom into those. Starting off with the uh, outermost, we have the tympanic membrane. This is what is going to separate your outer from your inner ear. The tympanic membrane is that thing that you've definitely injured with a Q tip at least once. It is your eardrum. Then you have these three structures right here, the incus, the malleus, and the stapes. These are going to be your ossicles. These are the smallest bones of the body. The purpose of these is to take a uh- the purpose of these is to deform in response to activation or stimulation or pounding on the tympanic membrane, and then passing that movement onto the oval window. The oval window is going to lead to the inner ear, to the cochlea and the vestibule. So, quick thought, going back about the ossicles, the ossicles evolutionarily are actually your modified gill bones. So your very very early ancestors, hundreds of millions of years ago, when they first left the ocean and got onto dry land, the bones that were originally for the gills uh, turned into your ossicles with descent through modification. So, that's a cool fact, I really enjoy that. Um, but the cochlea is going to be the site of the hair cells, is what it is going to um, be responsible for sound, the vestibule is going to be responsible for orienting yourself in 3D space. So you have your cochlear nerve associated with the cochlea. And then what do you think the vestibule is going to be associated with? Well, it's going to be associated with the vestibular nerves. So you also have the semicircular ducts or canals, they're going to work kind of like a craftsman's level. There's going to be, um, things that are going to orient them. You can see here you have three of them, they're going to be on the X, Y, and Z axis. And so fluid is going to move around within those, allowing you to orient yourself on all three of those axises. Now let's talk a little bit more about the cochlea itself. Oh- [audio cuts] Alright, now let's take a look inside the actual cochlea. The cochlea is kind of a conch-shaped organ, it's kind of a shell-shaped organ. And so here, let's take a cross section of that and take a minute to really appreciate what that looks like. So, you have three scalas, you have your scala vestibula, scala tympani, and then the one in the middle is going to be your scala media. So the idea behind having three scala here, three compartments, is that by having three, you can increase pressure and thus increase the sensitivity of the scala media, and the tympanic membranes we'll talk about in a second. Um, we can increase their sensitivity to changes in pressure. So, um they're all going to be filled with something called paralymph, paralymph is essentially just interstitial fluid. The scala media is going to be filled with endolymph, which is going to be similar, but it's going to have um, a higher concentration of electrolytes, specifically potassium. And now why do you think that might be? Well, the reason why is because the scala media is going to be the site of the actual hair cells and so having a lot of potassium there is going to facilitate their activation in response to stimuli. So um, the site of activation is something called the organ of Corti. You can see it there. Uh, the organ of Corti is going to consist of the hair cells, the basement membrane, and the tectorial membrane. The tectorial membrane is going to be pushed down when there is a change in pressure and that is going to push on the hair cells, the sertoli cells you might see them as, I'll get rid of that, that's going to push down on the hair cells, and that actual deformation is going to indicate to the nerve that it's time to activate and send that signal forward. So the actual sending of that signal is accomplished by a change in the shape of the hair cell, or a pushing on the hair cell. And that's what we mean by mechanoreceptor. It's going to be a change in response to um, a mechanical change in the environment around it. So let's show you what that histology looks like. Here we have our three scala. Here we have our hair cells, which are going to be on the basement membrane. Then we have our neural ganglion right over here. So, these are the labels that you'll probably have to know. I just wanted to show you a histology slide just because this tends to throw people for a little bit of a loop. Um, the area around these scala is going to be a dense connective tissue, but it doesn't necessarily look like connective tissue. So, I just wanted to show you that just so that it's a little bit more clear. So let's trace that signal through the- through the brain. So we have our vestibule in your- and our cochlea in the inner ear. Those are going to be associated with the cochlear and the vestibular nerve. Um, those you might see as one structure, you might see it as vestibulocochlear nerve. You might see it as two, but I keep it as two just because I think that's simpler. Um, it's going to be routed through the brain stem, through the caliculus, and then it's going to be processed in the temporal lobe. That's also going to be the site of um, uh that's also going to be the site of the language center of the brain as we've talked about, so that's how that signal is going to move. Cool- [audio cuts] Last one, big one, one that we've seen a little bit before. This is going to be vision. Vision is a type of photoreception, meaning that the nerves, the um, receptors are going to be activated by uh, light. They have photoreceptive proteins called rhodopsins, which are going to allow you to respond to light. There's also a few associated cranial nerves. We've talked about these before but bears repeating. The optic nerve is going to be right there. You're also going to have your trochlear nerve which is going to be highlighted. Trochlear nerve is going to be responsible for helping to move some of the muscles of the inner eye. Then we have our abducens, which is not going to be shown, but it's going to be associated with those muscles. Now, you don't have to know the individual muscles, but I put them here just so that you can see them. Cool. So uh, the structure of the eye, there's a few major structures here. If you can know this diagram, you know the eye well enough for this class. So starting at the anterior and moving to the posterior, we have the cornea. The cornea is going to be the outer cover of the eye. Um, inside of that, we're going to have the pupil. The pupil is not a structure in and of itself, the pupil is actually just an opening in the iris. The iris is the colored muscle that um, is going to be in the anterior. So this is what gives your eye color. It's going to expand and contract in response to light. I don't imagine that's terribly shocking to anyone at this point. I know that most people have seen at least a basic anatomy of the eye before. You're also going to have your ciliary bodies which are going to hold your lens in place. It shouldn't come as a shock that you have a lens. But it's actually kind of interesting what this looks like on the actual dissections. It's a lot harder than you might think. It's a lot more um, it's a lot tougher than you might think it is. And so all of those structures are going to be in the aqueous humor. The aqueous or water like humor of the brain. Moving back to the vitreous humor, we're going to have um, the vitreous humor itself is going to be a jelly-like substance. But then the big, big area here, the two big things that I hope you can uh, understand about the vitreous humor, first is going to be the retina. The retina is going to be that lighter colored material that is pushed to the back of the eye. It's going to have blood vessels, it's going to have photoreceptors, et cetera, et cetera. And then you're going to have an optic disc, which is going to be the site with the optic nerve. Or it's going to be near the site where the optic nerve actually attaches to uh, the eyeball itself. So, we talked about this before. Um, aqueous humor is water-like, vitreous humor is glass-like, here they are, um, they're both going to be transparent to allow light to come through, cool. That fovea is going to be the blind spot of the eye. Once again, it's not exactly where the optic nerve is going to attach, but um, the optic disc is going to be right in front of it, cool. So moving on to rods and cones. These are the actual photoreceptors themselves, you have two types. Rods are going to resolve for total density of light. You have approximately 130 million per eye. Cones are going to resolve for wave length or quote-on-quote "color." This is what allows for color vision. And you have less of them, but you still have a good amount. Um, they are going to be um, found in the retina. The retina is probably the most important structure of the posterior of the eye. It is a thin, delicate membrane. It's a very light color. You'll be able to bisect it from the rest of the eye during today's lab. It's actually only kept in place by back pressure from the vitreous humor. And so for that reason, it'll begin to fall apart and it'll begin to detach from the back of the eye as you remove that vitreous humor so, cool. So, before we move on to the dissection, let's talk very briefly about the signal transduction from the eye to the visual cortex. So, we have rod cells and cone cells in the eye that's going to go to the optic nerve, the big structure there is the optic chiasm, that is where the cross linking is going to occur. Cross linking, by the way, means that information taken from the left eye is going to be processed on the right side of the brain and vice versa, so, that's where that occurs. Then we have the thalamus which is going to be deep to this area. But once again, just keep in mind you don't need to know the individual nucleus, just know that it's the thalamus. Then the superior caliculus, which is going to be uh, one of those structures that we talked about last week, talked about it again this week. Um, we're going to see it on the actual dissection in a sec, you can run your finger across it and feel the actual texture of it. And then it is going to finally be processed in the primary auditor- excuse me, primary visual cortex of the occipital lobe, cool. So um, we don't have as much of a clear structure, like a clear list of structures we want you guys to know. But here is um, here is what I think is useful so, cool. Here's a full list, I'll use that as our review for this week. And with that, let's move on to the dissection. [Silence] Alright, and now we uh, have this week's dissection. This is the eye. Uh, this is the eye, once again, of a sheep. Um, you can see that it has some, some, uh, superorbital fat right here, some uh, orbital fascia. Here's the eyeball itself. Here's just some of the tissue that surrounds it. Um, these are going to be a little bit different shaped than they would be in the living organism. As you can see, this one is kind of crushed to the side. Uh, that's just because they lose pressure and then some of the proteins will harden in a position that doesn't necessarily reflect how it would look when it's alive. But what we can see here is we can see the aqueous humor upfront and the vitreous humor we'll see in just a second. But we can see the cornea, that's going to be this area right here. Um, the iris is not going to be visible. Um, these are going to be a little bit cloudier than they would be when the animal was alive. Just because these proteins have once again degraded, it hardened so, cool, let's uh, let's pop them open. So, once again the two major humors of the eye are going to be the aqueous humor, which is going to be anterior, and the vitreous humor, which is going to be in the back. The first cut that we're going to do is going to be to separate the two. And before you do that, when you have your eye in front of you, it may benefit you to trim away some of this extra fat, it may uh, benefit you to trim- excuse me, may benefit you to trim away uh, some of this hair, these are the eyelashes right there, but for this eye, it looks pretty good, so we will just go ahead and cut it open. The way that I like to do this, once again, is uh, make sure not to cut towards yourself, make sure you're not pointing the scalpel towards anything you care about. So I will hold the eye sideways and I will make that first incision. It's again, little strokes like this, right? [Silence] And you should feel a change in pressure. And if you look very closely, you can actually see the fluid leaking out. That is going to be the aqueous humor. Cool, cool. Once we have a good, uh cut, good place that we can grab onto, I think it's generally safer to switch to the scissors. So I will cut these guys open a little bit more. [Silence] Get some more aqueous humor coming out. Good, good, good. Cool. Once again, these do pop when you first cut into them, so be sure to do it gently. Um, you don't want to get fluid in your eyes or on your face or anything like that. It is not formaldehyde, it's a safer version, but it is still extremely gross and I don't want to put that through you. Also, once again, just make sure that you're not cutting towards yourself because we haven't had any accidents with scalpels yet. And I would like to keep it that way. Cool. [Instruments shuffling] I'll probably end up cutting this. I- I think you get the idea. [Scissors snipping] Actually as we cut into it now, you can start to see uh, this structure right here, this hard round structure, I'll bring this a little closer. This hard round structure that I have just kind of dissociated, That's going to be the lens, so you can see the ciliary bodies that are attached to it right there. But that is indeed the lens. Cool, cool. [Scissors snipping] I'm gonna cut this down. [Scissors snipping] Holy shit, that was such a choppy job. [Instruments shuffling] There we go. And I'll probably cut the video there just so that we can uh, save a little bit on time. So now we have disarticulated the front from the back of the eye. We can see the lens is going to be this guy right here. And it will pop out now that we have sort of uh, destroyed those ciliary bodies. We can see where the iris would be, it's going to be this- I'll hold that a little closer, iris would be uh, this area right here, right, these structures, it has kind of a wavy pattern to it. I don't know if that's focusing correctly, but iris is going to be right here and then the pupil is going to be that area right there. The cornea is going to be this clear substance. It's going to be a little foggy on your eyes because these have obviously been um- these, the proteins will no longer be how they would when they were alive. Once again, because of protein degradation and protein accumulation, The iris is going to be a little bit cloudier- or, I'm sorry, the um, the cornea is going to be a little bit cloudier than it would have been. But moving back down, we can see this jelly-like substance. I don't know if you can see that on my pointer. Oh, there it is and I'll put it right there. That is going to be part of the vitreous humor. So this is the glass-like humor, the jelly-like humor. So once again, front of the eye, we can see it there. We have our ciliary bodies, our lens is right here. Uh, iris is right there, pupil is right there, and then the cornea is on the outside. Moving on to the back, we actually have a few interesting structures here. We have the retina, which you can see is going to be able to be peeled away. And then there's going to be one spot where the retina is not going to be freely dissociated, and that is going to be uh, the optic disc. So we can see this guy right here where my pointer is. This is the part of the retina that will not freely dissociate and now I will pull it off and you can see optic di- Jesus, optic disc is right there. Cool cool, so this little dot right here is going to be your optic disc. Once again, there's another layer here, uh, humans don't have that. That just helps nocturnal animals see at night. We once again don't have that layer, but then we can see the back of the eye right there. Another cool thing to do, another interesting cut that you can make, I don't know if this one is going to be the best example, but if you're feeling ambitious, you can try and bisect the back of the eye. [Silence] And you should be able to find- I believe there's a little bit of it on this one, you can find the optic nerve. Optic nerve is going to be right here on this guy, it is going to be right behind the optic disc. So if you bisect the optic disc, which uh, looks like it's going to be once again, right here on this fragment. If you bisect this optic disc, so cut right down that line, you should be able to find the optic nerve. Here we can see the end of it, so it kind of curves back towards the side. Um, you can find the optic nerve and then that is uh, the main sensory nerve. So that's a fun challenge to see if you can find that optic nerve. But otherwise, that is the whole dissection. Just want to bring you back before I go to this guy right here again, this is the lens. You'll notice that the lens is actually quite hard, so it takes a lot of force to deform this guy. It almost kind of feels like a hockey puck, and that's that. Cool, cool. And with that, I'd just like to say- and with that, I'd just like to say thank you guys so much for your attention and your hard work this semester. You still have the final to get through, but it tends to help people's grades rather than hurt them. You should have study materials for it available online. Good luck with everything and I will see you in 202.