For us human. And again the olfactory system of course begins with the nose right? Let's take a look. What happens? So when you have a wine and those chemicals will release from the wine and enter cavity through your nose, nasal cavity. And then these chemicals with activate the olfactory sensory neuron, actually on the top of the notes okay [FOREIGN]. And then this neuron transfers this signal into electrical signal and then will pass those signals to the brain and then we go to the cortex of the olfactory perception we have in there. And then of course the first step of this olfaction is actually these chemicals binding to these cilia off the olfactory sensory neuron in the notes. And then they are receptors, special receptor on the membrane and then that protein wheel will combine to this chemical. And then the receptor will be activated and then just so they can say the photo receptor right? Then they can produce the electric signal, okay? This is what happens. Here, there is another cartoon to show the organization, okay? Take a look here. These are this is a nose carried to, right? So in this region then we have the olfactory epithelium. This is [FOREIGN] it's just like very thin layer of the tissue. That tissue is of course a lot of neurons. Those neurons are olfactory sensory neurons to detect the chemical, just like in our eye there is a retina, right, that tissue. And then quite interesting, okay, so these cells, only one type of cells in this olfactory epithelium. In the retina, we have so many types, right? But here only one type, okay? And then they will send axon to the brain, directly to the brain, from here across these bones there is some kind of passageway or holes. Actually and axon can enters the brain. And and they make connections which is a brain neuron. And take a look here. This is the location where the, Olfactory detection happens is at those cilia. As we discussed last time, for the visual system the photoreceptor has a lot of commemorating, right. Those to you increase the surface area to catch the phone call. And here again the same thing happened, you see maybe the principles. So those are cereal, al lot of cereal to increase. The surface area to catch those chemical molecules. And take a look here. This is actually the real cilia of the cell. This is actually, you can see this is the one cell, the region. This region we call dendritic knot here. Okay, let's take a more complete view of this cell. Cell body here, and then axon go to the brain. And then there was a dendrite. Is a bipolar cell. Dendrites will go to the needs of cavity and then, from the dendrites and the end of the dendrites, there is a knock there is kind of twitching, you cannot. Now, Frontal Lobe, then a lot of cilia then begins, okay? This is a cilia, you can see. This is a [INAUDIBLE] and then it's the cilia. The cilia locate mainly in the mucus in your nose, okay? [FOREIGN] A lot of cilia actually are located here. And in that layer actually, you have a lot of things happen. You can see that when there are some chemicals in the air enter your nose. What would happen then? The chemicals need first dissolve in that layer of mucus. [FOREIGN] And then a lot of chemicals actually, the odorant is really hydrophobic. [FOREIGN] So it's difficult to dissolve in the in the mucus. And then we have a system we call the protein. There is some protein in the mucus. And then they can bind to the odorant chemicals. Molecules and facilitator to diffusion of those chemicals in the mucus. To bind to the receptor. It is called binding protein. Okay? So there of factor detection. As we mentioned, it only happens on this cilia region, okay? That means, those receptors or any other related proteins actually need to be highly enriched In this serous membrane region, okay? And let's take a look. How the olfactory detection begins? This is a cartoon to show the olfactory sensory neuron. Again, it's a bipolar neuron. You have the cell body, you have the axon, and you have the dendrite. Dendrite have a knob and then the cilia. Okay, the cilia, of course, inside. Those actually cytosomes, [FOREIGN] connected with this dendrite and the cell body, right? This is the on the membrane. Then you have a lot of proteins. Just so that they can photoreceptor into disc membrane. What do you have? You have receptor. Okay? This receptor needed to recognize some specific odorant molecules and bind those molecules and this receptor will activate by the odorant molecule then will activate a G protein. This G protein we call G, O. G, O L, F, in the photo receptor we have density protein also. Density protein is called transducing, okay, GT. Here is GO. The GO activated and this GO we activate with another enzyme called endnocyclase type 3-863. This is a specific one, is specific to the olfactory system. And they activate this enzyme. This enzyme will synthesize a second messenger called CANP. Sythensized from the ATP converted to CCAMP. And the CCAMP is the second messenger. Where bind the two to a channel called cytonucleotide channel. The CAG channel. Okay? And then bind to there, this channel will open. Open then whatever happened is sewed in calcium, we are going into the cell, and then the cell will depolarize okay. And then of course the fire action, potential, all right? But here, there's another quite interesting feature. That is when the sodium and the calcium come into the cell, they polarize the cell. And this is not the end of the signaling. There is another step quite interesting It is that this calcium, the intercellular calcium will again to actuate another channel, called calcium actuate co-act channel. So if you have a core channel activated, what will happen to the cell, typically? Like receptor, like a. Those receptors, especially is a core channel. And then mainly GABA is inhibitory effect, right? So yes. So here then, why you need this then? For the cell excitation, of course it's depolarization. If you have opened another channel, chloride channel and the hypochlorite to the cell [INAUDIBLE] Why you need these thing? It's strange, right? Adaptation. Okay. So, the signal increase and then, you somehow you need a shutdown the signal right? Okay good. So but actually here is quite unique to this system. This kind of canal does not have polarized a cell. It's actually again depolarized a cell. That's special here, okay? Why this quiet channel can further depolarize the cell, okay. We'll talk about it. First, let's look at it here. So first, the same transduction happens as should a cast G protein cascade Is the cell and another channel. First it'll depolarize the cell. This another beautification right? So we are this may be the step. And also this enzyme step and beautification, but in the olfactory system. Another, correct channel, further amplify the signal. If this is indeed a correct channel and also the open this channel you need that in fact this produce deprivation. So what conditions should hold for this quite concentration inside is it high or low? >> High. >> High? >> High inside. >> High inside. Why? >> So it can reach in [INAUDIBLE] flow out. >> Flow out. Okay. If a current flows out what happens to the inside? Is depolarized or hyperpolarized? Good, good, yes. So the answer is actually the inside you need to keep high concentration, relatively higher concentration than the extracellular side. And then if we open this channel, then we'll go out, then inside there will more positive because there's negative charge moving out, right? That's good. So how can you maintain a chloride concentration inside the hive, because in most neurons, in most case in the brain, the chloride concentration inside is quite low. This means if a chloride opens, the chloride ion should go into the cell. So this cell actually has a special exchanger called the sodium potassium chloride exchanger. And that one can really pump those from the outside to inside to keep it high
