Sensory System - Online Tutor, Practice Problems & Exam Prep

The sensory system processes environmental stimuli through specialized receptors. Mechanoreceptors detect physical changes, thermoreceptors sense temperature, and nociceptors respond to pain. Photoreceptors in the retina, including rods and cones, transduce light into neural signals, enabling vision. Sound perception involves hair cells in the cochlea, while chemoreceptors mediate taste and smell. Each receptor type contributes to our perception, forming a complex representation of reality, influenced by adaptation and localization of function in the brain.

Sensory Systems

Hi. In this lesson, we'll be talking about the sensory system, which is the part of the nervous system that receives and processes sensory information. It's going to be our body's way of identifying what's out in the environment and going to give us the information necessary to construct our realities. So the first step of this is going to be sensory reception, which is just the detection of some type of stimulus by sensory receptors. A sensory receptor is a type of nerve that responds to some stimuli and transduces a response as either a graded or an action potential. And it should be noted that sensory receptors only respond to very specific stimuli. For example, temperature within a certain range, or a light of a very specific type. Now sensory transduction is the conversion of that stimulus into some internal signal like a graded or an action potential. So our sensory receptors are going to transduce the signals they get, and, during transduction these signals can actually be greatly amplified. Now, the receptor potential is essentially a type of graded potential that's generated by the activation of sensory receptors. So these graded potentials will either depolarize or hyperpolarize the membrane potential of these nerves, and that will either lead to action potentials, or in the case of hyperpolarization prevent action potentials. And these, you know, action potentials, it should be noted are, you know, action potentials only have its like an all or nothing signal. They only have one signal that they can send, so the magnitude of these receptor potentials is going to be encoded in the frequency of action potentials that are issued. And over time, sensory responses to a stimulus can change, and we actually call that sensory adaptation. Adaptation. Now here you can see a bunch of different types of sensory receptors, and they come in a wide variety of shapes and sizes. The end takeaway here is that the receptors can vary greatly in function and structure.

And what I want to point out is behind me, how, for example, a sensory receptor will either depolarize or hyperpolarize. So in the case of the pressure receptors in our skin that we use to sense different types of touch, light pressure will actually deform these nerves and physically pull open channels that allow ions through. So light pressure will slightly open the ion channel and allow just a little bit of, in this case, sodium through. Whereas a big pressure will cause a great deformation, and allow a large amount of sodium to enter the cell, and result in a greater depolarization. Not every type of sensory receptor is going to work by some type of physical deformation that opens ion channels, but I think this conveys nicely the different ways in which magnitudes can be conveyed by the literal opening of channels. I mean, that's how these things are working.

Once the information has been transduced, it has to be transmitted or sent to the central nervous system. And sensory neurons will actually carry this information to specific parts of the brain because of localization of function. There are specific areas dedicated to processing sound, dedicated to processing visual stimulation. In fact, among visual stimulation, there are different areas that process different types of visual stimulation, like edge detection or motion. Now, this all sums together into what you would call perception, which is our brain's way of taking the sensory information, processing it, and turning it into a meaningful representation of a stimulus. So, the way we often think about the world is, I'm seeing the world around me, when in actuality that's not what's happening. What's happening is light is hitting the sensory receptors in your eyes, and conveys various signals to them, and then that information is taken to the optic cortex, right, or the visual cortex, and there it's processed. And then what you see as the world around you develops during that process. So really everything that you perceive as your reality is the world around you, is more or less in your imagination when you think about it. Because it's just a construct in your mind, and what you're perceiving as the world around you could in fact be very different from what someone else perceives as the world around them. One of the greatest examples that you can give of this is that when we see images, we're actually seeing them upside down. The way that light enters our eye and stimulates our sensory receptors there, we end up with an image that's the upside-down version of what's out in the world. Our brain is actually what takes that and flips it right side up. Just a nice illustration of how our minds are actually constructing what we consider our realities. Now with that, let's go ahead and flip the page, light stuff, right?

Sensory Receptors

There are many different types of sensory receptors, so let's go through some of the categories. Mechanoreceptors, or mechanical receptors, are like physical receptors. They respond to physical stimuli like pressure and physical distortion. So if I smush my finger, the sensory receptors that are picking up that information and sending it to my brain are mechanoreceptors. Now thermoreceptors respond to changes in temperature; they are temperature receptors if you want to think of them that way. Proprioceptors, kind of a weird group of sensory receptors, they actually respond to position and physical movement in the skeletal muscles and joints. And they're going to play a role in helping to maintain balance and body posture. Nociceptors, sometimes called pain receptors respond to tissue damage, and will potentially lead to pain perception, but not necessarily. Now chemoreceptors respond to various chemical stimuli, and this can come in a wide variety of forms, from the chemoreceptors in our nose responsible for our sense of smell, to receptors that sense capsaicin, which is the chemical in hot peppers that gives you that burning sensation. Now photoreceptors will actually respond to light or photons, hence their name. And you can see 2 examples of photoreceptors behind me. These are the photoreceptors found in our eyes, rods, and cones, and we'll talk more about these in just a little bit. And over here you can see some electroreceptors in these fish. These are receptors that respond to electric fields. So you can see here that the organisms use this to pick up on other organisms in their area because our bodies are electrically conductive. So here, this organism is going to sense the distortion in the electric field due to this other creature, and therefore sense its presence. Whereas an object, like a rock for example, isn't going to conduct that, and so it's not going to be alerted as it would if it picked up another organism in its area. And there's also magnetoreceptors, which, like electroreceptors that respond to electric fields, these magnetoreceptors respond to magnetic fields. Now let's actually go ahead and flip the page and take a look at a specific type of sensory receptor.

Hair Cells

Hair cells are sensory receptors used by the auditory and vestibular systems, and they'll actually respond to physical stimulation, which will result in the opening of ion channels. Surprisingly, the sensory receptors responsible for your perception of sound, your ability to hear, are actually responding to physical stimulation. Now, the reason they're called hair cells is because they have these hair-like projections called stereocilia that extend from the hair cells and are what will be physically manipulated in order to open those ion channels, which will result in a change in membrane potential. When these stereocilia are bent, there are ion channels located near their base that get pulled open due to the bending. Imagine a stereocilium like this; if it gets bent over, it will pull open this ion channel and allow some ions to go through. If we pull heavily on our stereocilia, depicted with three arrows to represent strong force, it will lead to more ions getting through, causing a greater depolarization. The actual bending, the grading of the bending, will affect the membrane.

Another interesting way these hair cells are used is in something called a statocyst. This is a balance sensory receptor used by, for example, marine invertebrates to get a sense of gravity. The ocean makes it hard to tell up from down without gravity, so this is their way of sensing gravity. The statocyst is a sac-like structure surrounded by hair cells. You can see all these hair cells each having numerous projections off of them, those are their stereocilia. Inside this sac of hair cells are what's called statoliths. These are crystals that will touch the hair cells to stimulate them. As you see here, our statolith will sink due to gravity, and wherever it touches the hair cells, it will cause stimulation, that will be transduced, and that signal will allow the organism to detect the direction of gravity's pull on the statolith and the statocyst.

Yet another fascinating way that organisms use hair cells is in the lateral line system. This system is found in some fish and amphibians and allows them to detect movements in water. The lateral line system has a canal that lets water in, and hair cells are located within. Here we have a zoomed-in version where these hair cells have a large dome over them known as a cupula. You don't need to worry about that detail; the key point is that water moving through these channels can lead to the stimulation of these hair cells, and consequently, these organisms can detect where the water is moving around them and thus have some idea of where, for example, another organism is relative to them. With that, let's actually go ahead and flip the page.

Hearing

Hearing is the perception that results from our ears transducing sound. Sound is a type of vibration that propagates as pressure waves moving through air or water. Now, waves have what's known as frequency. This is, the cycles per second of a wave. Here you can see a model of a wave, and one cycle would be one complete revolution if you want to think of that, of the wave. So if we start at this point on the wave and go all the way till we get to that same point again, that is one full cycle. Now technically, I should point out that this wave we're looking at here is a different type of wave from a pressure wave. A pressure wave is a longitudinal wave; this is a transverse wave. That's just for the physics people out there. For our purposes, it doesn't really matter because this is actually a much easier visual representation than what a pressure wave looks like. So, just know that one cycle is essentially one revolution of the wave if you want to think of it that way, and that perception of frequency, which is the number of cycles per second, comes in as pitch. That's basically like the notes of music you hear. Right? The different types of sound, the different scales of sound that you hear. That's just our perception of frequency.

Now the amplitude of these waves, which you can see here, this amplitude, is what we hear as volume. So the higher the amplitude of the wave the louder we perceive the sound to be. And our ear is the organ that will take in this sound and turn it into something meaningful for our brains. So, how does that happen? Well, the ear actually has 3 different parts to it: the outer, middle, and inner ear. The outer ear is basically just the cup that sits on the side of our head that is shaped to best gather sound and filter it into this tube. Now, this tube will end at what's called the tympanic membrane, this is the eardrum. It's a thin membrane that separates the outer ear from the inner ear and is going to essentially represent the first step of sound being carried into the body and turned into a meaningful signal.

In the middle ear, we have these bones, and these bones are going to be responsible for amplifying sounds that come from the environment. These bones are called ossicles, and there are actually 3 of them, and you can see them here. We have 1, 2, and 3, and these ossicles will move based on sound waves hitting the tympanic membrane, causing them to move, and basically, they're going to act like a kick pedal on a drum almost, and hammer against this structure, the oval window. Now, the oval window is a membrane-covered opening that leads from the middle ear to the inner ear. So we have these two membrane-covered openings. One that, you know, hits the ossicles and then the one that the ossicles pound on to essentially transmit sound. Now the ossicle that's actually hitting on the oval window is called the stapes. And I also want to briefly mention the Eustachian tube, that's actually what connects your middle ear to your nose and throat region, the nasopharynx. And whenever, if you've ever flown on a plane or had your ears plugged up before, that's from your Eustachian tubes. That's from pressure changes in the Eustachian tubes causing that sensation. So let's actually go ahead and flip the page and move on into the inner ear.

Inner Ear

The inner ear is the portion that actually contains the sensory receptors that are responsible for the detection of sound and are going to be involved in balance. Now, the balance-detecting system is called the vestibular system, and it's basically attached to the sound-detecting system. The vestibular system is made up of these semicircular canals, these three fluid-filled cavities that you can see here, on the inner ear structure. And essentially, fluid is going to move through these canals and stimulate hair cells in them, and that's how we're going to be able to detect rotational motion and get a general sense of balance. This is why, for example, as a kid, you know, when you spin around a lot and you get dizzy, it's because the fluid is still moving through your semicircular canals due to inertia, so you're still getting that perception that you're moving even though you've stopped. Now, the cochlea, this structure is what's going to be responsible for the detection of sound, and it's a spiral-shaped cavity, and it kind of looks like a cone that got coiled up. Now you can see, sort of, a modified version of the cochlea here, which is made to look like what the cochlea would appear as if it were uncoiled. That's why it's all straightened out. However, in reality, its structure is all curled up. So imagine, you know, taking this and then rolling it up like a fruit roll-up or something. Now, the cochlea has a bunch of different structures in it. You don't need to worry about all of this, but I'm just going to give you a general sense of what's going on in there so that we can talk about the part that you do need to understand. So the cochlea actually has three ducts in it, or three fluid-filled tubes. There's this one on top, we call the vestibular duct, there's the tympanic duct on the bottom, and then in the middle we have the cochlear duct. Now, the hair cells in the cochlea that are going to be responsible for detecting sound sit on something called the basilar membrane. This is the membrane, kind of in the middle of the cochlea, that's going to be underneath the cochlear duct and above this tympanic duct. But, really you only need to know about the basilar membrane because that's what the organ of Corti sits on. This is the structure that contains many hair cells. As you can see here, we have our organ of Corti, and all these little projections on top are our hair cells. And, these are the hair cells that are going to be stimulated to perceive sound. Now, it's worth noting that the basilar membrane is different in different regions of the cochlea. It will actually have different regions that vibrate at different frequencies of sound waves. And in this way, we're able to better perceive a wider range of sound frequencies. Now, how these hair cells in the organ of Corti are actually stimulated has to do in part with something called the tectorial membrane. This is going to be a little membrane, you can see it here, that sits above our hair cells, which are here in the organ of Corti. Now basically, when the stapes hits the oval window, it's going to send a wave through the fluid of the cochlea, and that fluid moving is going to vibrate those membranes, and those membranes are going to move when they vibrate. Right? It's kind of what vibrating means. But, that vibration of the basilar membrane is going to cause those hair cells to bend due to their connection with the tectorial membrane. Although, it's worth noting that not all hair cells are connected to the tectorial membrane. And I should point out that this process is not super well understood. So you know, in 10 years' time or something maybe what I'm saying will no longer be held as the standard of the day. So, you know, not totally well understood, but there is an interaction between those hair cells and the tectorial membrane, and it's those hair cells being stimulated that's going to lead to the perception of sound. And again, remember that the amplitude of the wave translates into volume, and the frequency of the vibrations translates into pitch. Now, I also want to point out that there's this structure called the round window, that's kind of all the way at the other end of the cochlea, and its job, it's a membrane-covered opening like the oval window, but its job is to dampen waves and prevent reverberation. Essentially, this is going to allow the waves to sort of diffuse their energy out of the cochlea, and make sure that they're not just reverberating or echoing around inside there. So, with that let's actually go ahead and flip the page.

Vision

Photoreception is the detection of light, and this is carried out by many different organisms. From us humans with our very complex eyes, to nematodes, you know, little roundworms in the soil that have photoreceptors that can detect the presence or absence of light. Now we're going to take a look at some more sophisticated systems that carry out photoreception, namely we're going to look at eyes. Now, insects and arthropods in general have an interesting eye called the compound eye. This is an eye composed of many little repeating units called ommatidia. And hopefully, you can see here all these little repeating units all over the eye. I mean, I can't even begin to dot them all. Those are all ommatidia, which are basically structures that contain clusters of photoreceptors.

Here we have what you could think of as a cross-section of the compound eye. So if we cut a slice into our compound eye, this stuff at the top represents the surface of the eye and these are all those subsurface structures. And, each one of these is an ommatidium.

And if we go over here, you can see a zoomed-in version of the ommatidia, and it's going to contain a cluster of photoreceptors, and that is how these eyes are going to detect light.

Now, the simple eye, which is just a single lens eye, is what we have. And this is going to operate similar to a camera, with its single lens. Now, the human eye can only perceive light in what's called the visible spectrum, which is just a small portion of the electromagnetic spectrum of electromagnetic radiation, which you can see down here. In fact, this visible light is not even close to proportional in this chart. The visible light is just a teeny little sliver on this huge range of different types of electromagnetic radiation.

Now looking at the eye, the white of the eye is known as the sclera. And this is basically a protective structure and it's going to be composed in part of collagen and elastic fibers to give it a tough resilient structure that can take a little squishing and motion.

Now, the cornea is basically the fluid-filled transparent cover over the iris and the pupil. It's kind of hard to see in a head-on image, but here you can see it as this area above the lens right here. Now, the iris is the colored area around the pupil, the pupil being this dark center of the eye, the iris is this region that I'm just kind of pointing out here. The iris is not just there to make our eyes look pretty and give them some color, it's actually there to control pupil diameter and lens shape, which is going to be very important for focusing light so that we can perceive a clear image.

Clearly, my eyes are incapable of that as I wear corrective lenses. I actually need a little assistance because my eyes can't quite focus the light properly.

Now, the pupil is that black hole as I said, and it's going to be the thing that allows the light to pass through the lens. So if you look over here, this structure is our lens and this opening here, that is on top of it, that is our pupil. It appears black because light is getting sucked in there, and black is of course what we see when there's an absence of light.

Now, the lens is going to actually change its shape to focus light from the cornea. However, the cornea itself has some strong refractive capabilities; we'll get into that in just a little bit. And essentially light is going to move through the cornea, through the lens, and then get focused onto the retina, which is the back of the eye that contains photoreceptors.

Let me jump out of the way here. So this area at the back of the eye is the retina, and light is going to enter cornea, get refracted through the lens, and project some image onto the retina. And that is where our photoreceptors are, and they will take it from there. So with that let's flip the page and actually see how those photoreceptors work.

Photoreceptors

These light signals are transduced in our photoreceptors in the retina, and we actually have 2 types in the human eye, rods and these other types called cones that we'll get to in just a moment. Now, rods are photoreceptors that are capable of detecting lower levels of light. However, they're not capable of detecting the color of light. So these are sort of like our black and white receptors. They're usually found around the outer edges of the retina, and make up more of our peripheral vision. But that's not the case with all organisms. For example, cats tend to have lots of rods in their retinas, and not just on the outer edges, so that they can see better in the dark. Since, you know, they are, or they tend to be nocturnal hunters. Now, rhodopsin is the light-sensitive receptor protein that's actually going to, you know, do the phototransduction in rods, and it's composed of 2 components, retinol and opsin. Retinol is a light-absorbing molecule, it's actually a form of vitamin A, that's why. Another reason it's important to take your vitamins, and opsin is a light-sensitive protein. Now, what's going to happen is retinol will absorb light, and this is going to rearrange its structure and cause a conformational change in opsin. And, basically, it's going to act as a G protein receptor that will lead to the opening of sodium ion channels, and you can see a little model of that here. So, if light, and I'm just gonna use a sort of lightning bolt arrow, if light strikes rhodopsin it's going to cause, retinol to absorb it, and that's going to cause a change in the structure, and here you see they'll actually split, and the opsin will go and, you know ultimately act as a G protein to open this ion channel, and you can see what a rod looks like, sort of big picture wise over here. You know it's not your typical looking nerve cell, it has some weird structures. It does have, you know, a synaptic body, and you know, cell body with the nucleus that's kind of normal looking, but you know, then this stuff all up here is just bonkers. And the rhodopsin is going to actually be stored in this outer segment that has these, enfolded membranes all through here. That's what that pink line is, these enfolded membranes, and that's going to contain the rhodopsin and have it ready to go when light strikes. Now, cones are the photoreceptors that we use for color vision, and unlike rods that can pick up low levels of light, these really function best in bright light. And, they use different pigments to absorb different wavelengths of light. You can actually see a really nice chart right here that shows you the absorption of blue cones, green cones, and red cones, the 3 types of cones we have in our eyes, and you know, maybe if you've ever seen, a projector with the 3 different colored bulbs in it, you might have noticed that those are actually blue, green, and red bulbs. Now, you can also see rods absorption here, kind of in the middle, in the middle of all these. However, I do want you to note that it's going to be, you know picking up light in, you know, a range that has a decent amount of energy. That's the only thing I want to convey there. Now, the fovea is a special part of the retina. It's a little pit in the back, sort of in the center of the retina, and it's going to be packed with cones. And this is so that as light enters the eye, the center of our, you know our field of photoreceptors is going to have tons of these cones, and that's going to be the central point for light to be focused on, and so that's going to give us the clearest possible image, you know, when we translate all those signals in our brain. And you can see a cone structure here. It's not terribly similar to a rod's, but it has that same component of the outer segment with the enfolded membrane that's going to contain the photo pigment, or rather the pigment used for photoreception. However, of course its outer segment is shaped more like a cone, whereas the rod's outer segment is shaped more like a rod, and scientists just aren't very creative when it comes to naming most of the time. So with that, let's go ahead and turn the page.

The Retina

Our retinas have 3 types of nerve cells: photoreceptors, bipolar cells, and ganglion cells. They're arranged in 3 layers, kind of like a stack. So here we have the back of our retina, and here is the front where the light is going to be coming from. Now, you'd probably expect the photoreceptors to be right up at the front to greet these waves of light coming in, but you'd be wrong. Evolution is not perfect, remember. So our photoreceptors are actually found all the way at the back. I'm just going to jump out of the way here so you can see what I write. These are photoreceptors, and you can see we have rods here, on the outer edges of our retina, and in the center is where we have cones. So, obviously, we have many more photoreceptors than are being shown here in this diagram. I just want to point out that the cones are concentrated in the center of the retina, remember in that area called the fovea, and the rods are more concentrated on the peripheries.

Now this middle layer, which has this yellow line through it here, is where our photoreceptors connect to the bipolar cells. And these bipolar cells, which you can see here, are going to bring information from the photoreceptors to the ganglion cells. And it should be noted that the ganglion cells take input from multiple bipolar cells. So in essence, ganglion cells are really receiving input from multiple rods and cones at the same time, because they synapse on more than one bipolar cell.

So, the way this communication works is, also, you know, has some interesting facets to it. That is that the photoreceptors and bipolar cells actually have graded potentials, not action potentials. But the ganglion cells are what, say, send action potentials. Here we have graded potentials sent through the photoreceptors create graded potentials based on the light coming in; they cause the bipolar cells to have graded potentials, and multiple bipolar cells synapse on a ganglion cell and they can lead the ganglion cell to actually produce an action potential. Now remember that the receptor potential is generated by hyperpolarization from the opening of ion channels, and that, this is, you know, a little strange, a little different from what we're used to. You know, normally we think of depolarization leading to an action potential, but in this case we actually have a hyperpolarization that will then be translated into an action potential by the ganglion cells. Now the ganglion cells' axons form the optic nerve and actually bring the information to the brain to be turned into something useful.

Now, the reason I went with this image, even though this one looks a little nicer, is because I just wanted to convey that the ganglion cells are going to be synapsing on multiple bipolar cells, which you don't really see too much of in this image. So, even though it's a little prettier it labels everything nicely for you. I wanted to make sure that, you know, I stress the point that ganglion cells are receiving inputs from multiple rods and cones.

Now this information, when it comes to the brain, you know, it has to be interpreted. It's just a mishmash really. You know, here we have a really nice image, I'll jump out of the way, so you can see it better, that sort of illustrates how this happens. So, here we have, you know, what the eyes are looking at. And the rods and cones are going to produce, you know, different outputs of that image. The rods are going to sort of form a black and white version, and then our cones are going to show colored versions. This is going to have to be processed, to detect different types of color and edges, you can see. And that's going to be played with in many different ways, and all of these different facets of the image are put together to actually develop something that looks like this. Essentially, different parts of the visual cortex are going to play with this information in different ways, and then that all has to be integrated.

It should be noted that we actually have what's called binocular vision. Right? We have two eyes, so we actually get two images of the world around us. And it should be noted that these images aren't exactly the same. Because if you think of each of our eyes as a camera, then our cameras are in very slightly different positions. But that is the key to our ability to perceive the world in 3 dimensions, or perceive a sense of depth, I should say. You see, by taking essentially two pictures from slightly different angles, our brain can compare those two images, look at the differences between them, and from that generate a sense of depth. So, pretty, sophisticated processing has to happen to this simple visual input in order to actually generate anything meaningful from it.

With that, let's go ahead and flip the page.

Smell and Taste

Chemoreception is the detection of chemicals, and it's mediated by chemoreceptors, which are what we'll use for our sense of taste and our sense of smell. These chemoreceptors change their membrane potential when a specific type of compound is present. Gustation is what we call our sense of taste, and this is mediated by taste receptors, which are receptors in the taste buds on the tongue. They'll respond to molecules called tastants that stimulate these taste receptors. And there are going to be different varieties of tastants that correspond to the different flavors we can perceive. Those flavors are salt, sour, sweet, what's called umami, and bitter. The flavor of salt comes from tastants that are electrolytes, specifically sodium. Acids, specifically, hydrogen protons, will result in these, taste sour. Carbohydrates, like glucose, will taste sweet to us. Umami, which is sometimes described as the 5th taste and is actually a Japanese word, comes from proteins and amino acids like glutamate. That's that sort of, you know, taste you get, for example, from eating like a greasy burger or something, that unctuous umami flavor you get from the meat. It's just tasting the proteins in there, really. And bitter is used to identify poisonous compounds. That's why we have that, awful taste of bitter that makes you go blah. Blah. It's, you know, an evolutionary mechanism to hopefully get you to reject poisons based on their taste. Here you can see a taste receptor, or rather a taste bud with taste receptors in it. And this taste bud will be found all over the tongue here. And it's worth noting that salt and sour receptors actually have the same ion channels to detect their taste tense. Interesting to note because they're both looking for ions. Right? Now olfaction is what we call our sense of smell, and this is mediated by olfactory receptors, which are chemoreceptors that bind odorants. Odorants are like tastants for our nose. They're airborne molecules that are smelled. And essentially, these odorants will make their way into our nose where they will bind to olfactory receptors. Now, we have this special part of our brain called the olfactory bulb. In humans, it's not nearly as big as it is, for example, in rodents where it's a massive structure. This is the part of the brain that allows us to process this, smell information. And we actually have these, areas called glomeruli, where olfactory neurons of the same receptor converge. So, here in this figure you can see we have all these different types of receptors along here. Now, you can see that they are all different colors. However, you know, in this model the blue receptors are all going to be picking up the same types of odorants, the red receptors are going to be all picking up the same type of odorants, and the green receptors are all going to respond to the same type of odorants. So even though they're interspersed with each other, they're all going to converge in the different glomeruli up here. And you can see that those have been segregated, based on whether they're blue, red, or green. Now, it's worth noting that we actually, respond to a special class of chemicals secreted to the environment called pheromones. These are, you could almost think of like a very special type of odorant because they're signaling molecules and they'll actually affect the behavior and physiology of individuals in the same species. And we actually have a special part of our olfactory bulb called the vomeronasal organ that is specifically designed to, respond to those pheromones and has pheromone receptors. That's all I have for this lesson guys. Hopefully, now you have a little better understanding of how you see the world. Pun intended. I'm sorry. See you guys next time.