Reading Activity Week #13 (Due Monday)

The thing I found most interesting in chapter 13 is identification of smell. Unlike the other senses, we have a hard time figuring out the name for odors. This can be called the tip-of-the-nose phenomenon, which is the inability to name an odor even when we recognize it. This happens with speech, called the tip-of-the-tongue phenomenon, but we’re usually able to come up with other ways to describe the word, like what it starts with or what it sounds like. This isn’t present with smell. It’s believed that this is true because our sense of smell and language are very disconnected. With our other sensory systems, the information is processed in the thalamus before it reaches the cortex. This does not happen with smell. It’s believed that the thalamus is important with language. Therefore, smell does not usually influence our language and vice versa. This may also explain why we have few words to describe smells as compared to other sensory systems. I think this is really interesting because I’ve noticed these things before but never understood why. I also think it’s interesting how different our sense of smell is from our other senses.
Something I found least interesting is the theories of smell. One is the shape-pattern theory that says different scents activate different arrays of olfactory receptors and these arrays produce certain firing patters of neurons that decide which type of scent we perceive. This theory is the more dominant theory because it has more proof and is more consistent with our sense of smell. The other theory is the vibration theory. This theory states that every smell has a different vibrational frequency and that molecules in our nose that produce the same vibrations will smell the same. This theory is the weaker theory because it doesn’t explain how some smells can have the same frequencies but smell different. I think these theories are uninteresting because they don’t help me understand the concepts of smell, just what certain people think causes smells.
Three things I read that I think are most useful in understanding sensation and perception are odor (the smell sensation of a particular quality), specific ansomia (the inability to detect one certain smell, but have otherwise normal smell), and odor hedonics (the liking dimension of odor perception). I think that these three things are really useful because although they are specific concepts to certain parts of smell, they each help to describe how smell works and how it’s different in everyone.
One thing I found similar to other chapters is the olfactory epithelium. The book describes this part of the nose as “the retina of the nose”. This is because of the fact that it’s the part of the nose that detects odors in the air, just like the retina detects light and images.
Terms: olfactory epithelium, retina, odor, specific ansomia, odor hedonics, shape-pattern theory, vibration theory, tip-of-the-nose phenomenon, cortex

One topic that I found interesting was olfactory physiology. Before getting into olfactory physiology we have to define what olfaction is. Olfaction is the sense of smell. Olfactory sensations are called odors. Odors are general smell sensation of a particular quality. Not every chemical is an ordorant or an odor inducing substance. For a substance to be smelled a molecule must be able to float through the air, be small, and be repellent to water. Unlike touch and taste , the olfactory system is tacked onto an organ that serves another purpose. The primary purpose of the is to filter, warm, and humidify the air that we breathe. However, the inside of the nose has small ridges that cause a small amount of each breath upward into the olfactory cleft or a narrow space at the back of the nose into which air flows, where the main olfactory epithelium is located. After passing through the olfactory cleft it settles in the olfactory epithelium or a secretory muscosa in the human nose whose primary function is to detect ordorants in the inspired air. The Olfactory epithelium contains three kinds of cells supporting cells, basal cells, and olfactory sensory neurons. Supporting cells provide metabolic and physical support for the OSNs. Basal cells are precursor cells to olfactory sensory neurons. Olfactory sensory neurons are small neurons located beneath a water mucous layer in the epithelium. Another topic that I found interesting was on odor mixtures. Almost all of the olfactory stimuli that we encounter in the real world are mixtures. We are able to discriminate thousands of different odorants, but our intuition tells us that most mixtures are perceived to be single smells. An example of this would be the smell of cooking bacon. The smell from this is a combination of smells but our intuition tells us that it is one smell. One topic that I did not find very interesting was the section on olfactory hedonics. I thought that this section was difficult to understand. Another topic that I didn’t find very interesting was theories of olfactory perception, I thought it was difficult to understand. One topic I would like to go over more in class is olfactory physiology and from chemicals to smells.

Terms
Olfaction, Odor, Odorant, Olfactory cleft, Olfactory Epithelium, Supporting Cells, Basal Cells, Olfactory Sensory Neurons.

Chapter 13 Olfaction is about the sense of smell. It is the one of the chemical senses, the other is taste. Interesting thing is that olfaction has some unique physiological properties, for instance, only 35% of the genes that code for olfactory receptors in humans are functiona. Also the feel of scent which is that oftentimes odors have a feel- the trigeminal nerve that transmit information about the feel of an odoroant (menthol feels cold, cinnamon feels warm) the same as pain or irritation sensation-ammonia feels burning). Thus, how the biological interaction between odorant and neurological prcessing result in the psychological perception ? There is a theory of olfactory perception where odorant molecules have different shapes and the odorant will be detected by specific OR (olfactory receptor- the region on cilia of olfactory sensory neurons where odorant molecules bind) top the extent that the odorantnts molecules fit into. I also found interesting talking about memory and emtions, if the emotional context is good the odor will be liked , if its bad, the odor will be unliked. It is all connnected tot he memory as well as seeying, touching, etc. Limbic system is responsbile for that.
The least interesting topic was the [hysiological part of the sense of smell.

Terms:

olfaction, odor, odorant, OR, retina of the nose, limbic system, shape pattern theory, trigeminal nerve

Our olfactory system is in charge of our sense of smell. The sensations that this system receives is in the form of odors. The specific chemical compounds that are responsible for smell are called ordants. It makes sense to me that ordants must be volatile in order to be smelled and hydrophobic but I would like to learn more about what chemical properties determine if a scent can be smelled or not. Interestingly the function of the nose is not smell but it serves to filter, warm, humidify and clean the air that we breath. When air inters the nasal cavity it contacts little ridges called turbinates that cause a small bit of air to rice through the olfactory cleft (narrow space at the back of the nose). On the olfactory cleft there is a mucosal membrane called olfactory epithelium which is responsible for detecting scent. Inside the olfactory epithelium there are supporting cells (provide metabolic and physical support for olfactory sensory neurons), basal cells (precursor to olfactory sensory neurons), and olfactory sensory neurons ( small neurons underneath a water mucous layer) containing cilia and receptor sites for ordants. I found it very surprising that in order for an action potential to be initiated seven or eight odor molecules must bind to a receptor and about 40 impulses must be initiated in order to smell. I also found anosmia interesting, especially due to head trauma. The cribiform plate has axons from the olfactory sensory neurons that go through the little holes on it on the way to the brain. If the cribiform plate is damaged it is replaced with scar tissue and it cannot regenerate after it dies like it usually does. When the axons go through the cribiform plate they come to together to form the first cranial nerve (olfactory nerve) and inter the olfactory bulb (extension of the brain above the nose). Olfaction is different from other senses in that the olfactory bulbs (one on each side) are ipsilateral instead of contralateral. The olfactory bulb contains mitral cells and tufted cells which from glomeruli (spherical bundles containing axons of olfactory sensory neurons). The limbic system contains the primary olfactory cortex, amygdala-hippocampal complex and entorhinal cortex which all help to process the olfactory information that is sent. The olfactory system is directly connected to the brain but Olfactory sensory neuron axons are thin and very slow at conduction therefore making our sense of smell a relatively slow process compared to other senses. I thought the author made an interesting point about the importance of smelling and the fact that many people fail to realize the importance of it. Sense of smell is related to the quality of life and problems such as asmonia have been linked to depression. Another interesting phenomena is when you smell something at it feels cool or burns. This is due to the trigeminal (V) nerves which gives us feelings associated with certain cell. I thought the shape-pattern theory or the theory that says that the shape of odorant molecules and their receptors dictate the binding of specific receptors to odorant which determines what we smell made sense. However, the vibration theory which says that each scent has a different vibrational theory seemed a little strange to me and I would benefit from further explanation. Another way that our sense of smell is similar to other sensations is that often times we smell mixtures just like we can see mixtures of colors or hear mixtures of sounds instead of pure tones. The authors explain that there are not specific olfactory receptors for bacon but instead we sense a combination of different chemicals and recognize the combination as bacon.
Term: ordants, turbinates, mucosal membrane, ipsilateral, cribiform plate, trigeminal nerve, olfactory nerve, olfactory system,

I've always thought smell was interesting because you hear that it is the sense that is closest tied to memory. The olfactory bulb, the area in the brain that processes smell stimulation as soon as it is collected, is located directly above the cribiform plate. This is the thin bone that seperates the brain from the olfactory epithelium, the membrane that is laced with chemical receptors designed to detect odors. The cribiform plate is perforated and olfactory receptor neurons receive signals from the receptor sites located on their dendritic cilia, and carry these signals through the bone plate and bundle together into the olfactory nerve before transmitting to the olfactory bulb. The fact that the olfactory bulb is ipsilateral is interesting because almost all other brain to body connections are contralateral. I believe that the smell function is very primitive and appeared early from an evolutionary perspective. I think that the ipsilateral transfer from nose to brain speaks to how much our brain relied on localization of function when the ability formed. For whatever reason most of our brain developed contralaterally, but smell developed when our brain was very simple, and evolution has shown that in this case the simplest method has worked best. It must have because it hasn't changed while the brain has undergone massive evolutionary changes. It is also cool that each individual smell has a glomurulus detector. So each individual odor sensation, the book uses mint as an example, has a bundle of neurons dedicated to deciding on whether this particular odor is present. If these neurons are prewired to detect specific chemical compounds causing specific odors, then they must have been formed after birth, or we must be born with them, but then how do our genes know what smells we will need to be able to experience?

The trigemeninal nerve seems to integrate all the chemical, temperature and pressure sensory information coming from the bottom of the face, the nasal and mouth area, and transfer the data to the thalamus. I cannot tell if this is independent of the signals being transported through the olfactory bulb, could possibly cover that in class. The shape pattern theory holds that chemical triggers for our odor detectors have unique shapes and the receptor sites are shaped in such a way that allow the odor chemical to bind to that receptor and that receptor alone. The shape of both the chemical and the receptor only allow an interaction between those specific pairs. The vibration theory holds that every molecule is vibrating at a very specific frequency and the receptors are sensitive to specific frequencies, so any molecules that emit the same vibration frequency are perceived as the same smell. I personally believe that the chemical receptors in our olfactory epithelium are sensitive to particular chemical groups and a molecule that contains this group will be able to bind to the receptor. To be an odorant a chemical must be volatile, or able to be dispersed by air, and repellent to water. I bet there are active groups that are common among molecules that fit the properties an odorant needs. The book describes this somewhat as feature detection.

Tip of the nose state is when you recognize a smell but cannot recognize what the smell is. There seems to be some kind of sensory memory but the verbal memory is not present to describe the experience in the way it was associated. The brain is only aware that an association was made. Adaption occurs when you become unable to perceive an olfactory sensation after being exposed to it for a period of time. The receptors essentially become fatigued after binding to chemicals, shrinking into the cell body for a refractory period before being able to bind to another odorant. After a long period of time there are probably not enough receptors that are unfatigued to send action potentials. Without enough action potentials neurons later in the process are not able to detect smell, so we do not experience it.

Cognitive habituation seems to be adaption in the long term. When exposed to an odor for extended periods of time the brain seems to no longer produce nearly as strong of a reaction. The pattern for this particular smell is recognized early on and the brain does not spend the energy to process this stimulation fully because it just assumes that everything is normal.

Terms: olfactory bulb, cribiform plate, olfactory epithelium, glomurulus, trigeminal nerve, shape-pattern theory, vibration theory, feature detection, tip of the nose state, adaption, cognitive habituation

The stimuli for olfaction are small, airborne molecules, which might be pumped into the air from a perfume bottle or released from a solid substance, such as a food. When these molecules waft up to the top of your nasal cavity (right), they make contact with receptor cells that very quickly send information about the substance you are smelling to the brain. Olfaction is a paradoxical sense in some ways. We can have powerful emotional reactions to smells, and a smell from your past may instantly trigger a vivid flashback memory of an event or setting. On the other hand, we have great difficulty naming even very familiar smells, and when multiple molecules are mixed together, the resulting smell is usually perceived as qualitatively different than the smells of any of the component molecules alone.

What I found most interesting is the concept of olfaction, memory and emotion. The key to olfactory associative learning is the experience that occurs when the odor is first encountered, and in particular, the emotional connotation of that experience. When an odor is liked or dislike because of what it has been associated with in our past, we are also recalling a memory when we smell it. Many of our odor experiences are too vague to conjure specific memories, and only the feelings of good or bad remain. However, on of the most distinctive features of olfaction is its ability to elicit our most emotional and evocative personal recollections. When it comes to neuroanatomical and evolutionary connections between odor and emotion, the amygdale, which synapses directly with the olfactory nerve, is critical for emotional associative learning. The orbitofrontal cortex, the part of the frontal lobe of the cortex that lies above the bone (orbit) containing the eyes. The orbitofrontal cortex is responsible for processing olfaction. It is also the area of the brain critical for assigning affective value to stimuli—in other words, determining hedonic meaning. Only in human do we have visual and auditory info mostly replaced by smell for imparting crucial knowledge about the world, yet our olfactory system has retained some of its basic functions. The most immediate responses we have to odors are simple binary opposites: like or dislike approach or avoid. Emotions cover similar messages: approach what is good, sage and joyful, and avoid what is bad, dangerous, or liable to cause grief. Moreover, when it comes to vomeronasal organ and the question of human pheromones, animals that rely on smell for survival, the olfactory system consists of two subdivisions: the main olfactory bulb and the accessory olfactory bulb. Main olfactory bulb (MOB): The olfactory bulb; the blueberry-sized extension of the brain just above the nose; the first region of the brain where smells are processed. In humans we simply refer to “olfactory bulb(s),” but in animals with accessory olfactory bulbs, we distinguish between “main” and “accessory.” Accessory olfactory bulb (AOB): A smaller neural structure located behind the main olfactory bulb that receives input from the vomeronasal organ. The AOB is an add-on to the back of the MOB. Neurons from these two systems don’t interconnect, and the two systems function separately in the integration of specific chemicals. In order for the AOB to be activated, a structure different from the nose needs to be engaged., this structure is called the vomeronasal organ. vomeronasal organ (VNO): A chemical sensing organ at the base of the nasal cavity with a curved tubular shape. The VNO evolved to detect chemicals that cannot be processed by the olfactory epithelium, such as large and/or aqueous molecules—the types of molecules that constitute pheromones. The VNO is found in some amphibians, most reptiles and many mammals. In animals that possess a VNO, its primary function is the detection of pheromones. Pheromones are not odors. They are chemicals that may or may not have a smell. A pheromone is a chemical emitted by one member of a species that triggers a physiological or behavioral response in another member of the same species. Pheromones are signals for chemical communication and do not need to have any smell. Pheromones produce two kinds of effects. The two types of pheromones that cause these effects are known as releaser and primer pheromones. Releaser pheromone is a pheromone that triggers an immediate behavioral response among conspecifics. Primer pheromone is a pheromone that triggers a physiological (often hormonal) change among conspecifics. This effect usually involves prolonged pheromone exposure. Releaser pheromone effects are fast and always produce behavioral responses. In contrast, primer pheromones may produce no behavioral consequences and my be noticeable only in terms of physiological changes.

What I found least interesting was the concept of olfactory physiology. Olfaction is the sense of smell. Olfactory sensations called odors which is a general smell sensation of a particular quality. The stimuli for odors are chemical compounds. However, not every chemical is an odorant, any specific aromatic chemical. To be smelled, a molecule must be volatile and hydrophobic. When it comes to the human olfactory apparatus, the human olfactory system is tacked onto an organ that serves another purpose. The primary function of the nose is to filter, warm, and humidify the air that we breathe. But the inside of the nose has small ridges called trubinates that add turbulence to incoming air, causing a small puff of each breath to rise upward, pass through a narrow space called olfactory cleft and settle on a yellowish path of mucous membrane called the olfactory epithelium. Olfactory cleft is a narrow space at the back of the nose into which air flows, where the main olfactory epithelium is located. Olfactory epithelium, a secretory mucosa in the human nose whose primary function is to detect odorants in the inspired air. Located on both sides of the upper portion of the nasal cavity and the olfactory clefts, the olfactory epithelium contains three types of cells: olfactory sensory neurons, basal cells, and supporting cells. We have an olfactory epithelium at the back of each nasal passage. Each epithelium contains three types of cells: supporting, basal and olfactory sensory neurons. Supporting cells provides metabolic and physical support for the OSNs. The basal cells are precursor cells to olfactory sensory neurons. The main cell type in the olfactory epithelium. OSNs are small neurons located beneath a watery mucous layer in the epithelium. The cilia on the OSN dendrites contain the receptor sites for odorant molecules. These cilia, which are actually the OSN’s dendrites, have olfactory receptors on their tips. OR are the regions on the cilia of olfactory sensory neurons where odorant molecules bind. Furthermore, the axons on the ends of the OSNs opposite of the cilia dendrites pass through tiny sieve like holes of the cribriform plate, a bony structure riddled with tiny holes, at the level of the eyebrows that separates the nose from the brain. The axons from the olfactory sensory neurons pass through the tiny holes of the cribriform plate to enter the brain. A hard blow to the front of the head can cause the cribriform plate to be jarred back or fractured, slicing off the fragile olfactory axons, and consequently inducing anosmia (smell blindness), the total absence of a sense of smell. In someone with a healthily functioning sense of smell, the OSN axons pass through the cribriform plate, bundle together to form the olfactory nerve, the first pair of cranial nerves. The axons of the olfactory sensory neurons bundle together after passing through the cribriform plate to form the olfactory nerve. Olfactory bulb the blueberry-sized extension of the brain just above the nose, where olfactory information is first processed. There are two olfactory bulbs, one in each brain hemisphere, corresponding to the right and left nostrils. We have two olfactory bulbs, on in each brain hemisphere. Unlike the other senses, olfactision is ipsilateral, meaning that the right olfactory bulb gets information from the right nostril and the left bulb gets info from the left nostril. Within the olfactory bulb are globular tangles of axons from the OSNs that are synapsed with dendrites from mitral cells and tufted cells. These spherical bundles are called glomeruli. mitral cells the main projective output neurons in the olfactory bulbs. Tufted cells a secondary class of output neurons in the olfactory bulbs. Glomeruli spherical conglomerates containing the incoming axons of the olfactory sensory neurons. Each OSN converges onto two glomeruli (one medial, one lateral). Central brain structures that process olfactory info from the olfactory bulb include the primary olfactory cortex, amygdale-hippocampal complex and entorhinal cortex. Primary olfactory cortex: The neural area where olfactory information is first processed, which includes the amygdala–hippocampal complex and the entorhinal cortex. Amygdala–hippocampal complex, the conjoined regions of the amygdala and hippocampus, which are key structures in the limbic system. This complex is critical for the unique emotional and associative properties of olfactory cognition. Entorhinal cortex a phylogenetically old cortical region that provides the major sensory association input into the hippocampus. The entorhinal cortex also receives direct projections from olfactory regions. These are all part of a network of brain strutures known as the limbic system, which is involved in many aspects of emotion and memory. Moreover, olfactory receptor cells are different from all other sensory receptor cells in that they are not mediated by a protective barrier and instead make direct contact with the brain. By contrast, visual recepots are protected by the cornea, receptors for hearing are protected by the eardrum, and taste buds are buried in papillae. There are distinctions among sensation and perception. Sensation occurs when a scent is neurally registered; perception occurs when we become aware of detecting the scent.

Some things that are useful for understanding sensation and perception are pheromones, olfaction, and our memory. The topics that relate from other chapters include our senses, smells, perceptions, and our environment, such as what we pay attention to (selective attention).

Key terms: amygdala–hippocampal complex, anosmia, basal cells, cilia, cribriform plate, entorhinal cortex, glomeruli, ipsilateral, odor, odorant, olfaction, olfactory (I) nerves, gustation, olfactory bulb, olfactory cleft, olfactory epithelium, olfactory receptor (OR), olfactory sensory neurons (OSNs), supporting cells, mitral cells, tufted cells, primary olfactory cortex, limbic system, entorhinal cortex, orbitofrontal cortex, Accessory olfactory bulb (AOB), main olfactory bulb (MOB), vomeronasal organ (VNO), pheromone, releaser pheromone, primer pheromone.

This chapter is about olfaction which is the sense of smell. Olfactory sensations are called odors and is a general smell sensation of a particular quilaity. An ordorant is and specific aromatic chemical. Throughout time we have adapted to smell different odors especially those that can be harmful to us. We can't smell harmful smells that are ancestors didnt have a need to smell like carbon monoxide or natural gas. I thought it was interesting that companies are putting in smells with these now like the smell of rotten eggs, so that we can detect these harmful chemicals. I also thought it was interesting that the primary functiono of the nose is not to smell but to filter, warm, and humidify the air that we breathe. Air goes up through our olfactory cleft(a narrow space at the back of the nose into which air flows, where the main olfactory epithelium is located.) and then selttles on a yellowish patch of mucous membrane that we call the olfactory epoithelium which is like the retina of the nose. The olfactory epithelium is a scretory mucosa in the humna nose whose primary function is to detect odorants in the inspired air. located on both sides of the upper portion of the nasal cavityand the olfactory clefts, the olfactory epithelium contains three types of cells: olfactory sensory neurons, basal cells, and supporting cells. olfactory sensory neurons are the main cell type in the olfactoy epithelium. OSNs are small neurons located beneath a watery mucous layer in the epithelium. The cilia on the OSN dendrites contain the receptor sites for odorant molecules. Basal cells are precursor cells to the olfactory sensory neurons. Finally the supporting cells are a cell type that provides metabolic and physical support for the OSNs.
From the chapter i found quite a few things that were interesting. First i thought that snosmia was really interesting. Anosmia is the total inability to smell, most often resulting form sinus illness or head trauma. Smell blindness is linked to many neurological disorders like depression alzheimers, and parkinsons diseases. Sometimes loss of smell can be one of the first signs. If someone is depressed they often complain of a loss in smell and on the other side people that lose their sense of smell can become depressed. Loss of smell has also been linked to loss of taste. I found this part interesting because my grandma is one of these people without sense of smell or taste.
I also found dection, discrimination and recognition of odors to be very interesting. I never thought about it but i think its very interesting that we can picture certain foods and scents like flowers and laundry deterorgent but we cannot actually bring forth that smell without actually being around it. Professionals can discriminate up to 100,000 different scents. Another intersting fact was that by 85 50% of the population is anosmic because we are no longer producing the cells needed for smell. The staircase method is a psychophysical method for determinging the concentration of a stimulus required for dectection at the threshold level. A stimulus is presented in an ascending concentration sequence until detection is indicated and then the concentration is shifted to a descending sequence until the response changes to no detections. This method deteremines someone's odor detection threshold and is used to see if someone can discriminate one odor from another. The triangle test is where a participant is given three odors to smell, of which two are the same and one is different. The participant is required to state which is the odd odor out. The order is the three odors given is typically manipulated and the test repeated several times for greater accuracy. This test is to see if you can discriminate between two odors. I found it really interesting that our language and sense of smell are really not connected. Whenever i smell maple sryup i say i smell waffles and not actually maple sryup. I think the sense of smell and recognition is the strangest sense we have come across in the text. Tip-of-the-nose phenomenon is the inability to name an odorant even though it is very familiar. Unlike the tip of the tongue phenomenon with the nose we have no name of the odorant. Along with regonition i found adaption to be intersting. receptor adaption is the biochemical phenomenon that occurs after continuous exposure to an odorant, whereby the receptors stop resonding to the odorant and detection ceases. Also cross-adaption is the reduction in detection of an odorant following exposure to another odorant. Cross-adaption is presumed to occur because the two odorants share one or more olfactory receptors for their transduction, but the order of odorant presentation also plays a role. An example of this would be when you are shopping for purfumes. The salesperson will have you smell coffee beans to help you actually recognize each new fragrance that you are smelling instead of a mixture of each.
In this chapter the thing that i found to be least interesting was the human olfactory aparatus. I didnt like it as much as the rest of the chapter because it was all biology of the nose and i found how we actually perceived the odorants to be more interesting. I think this chapter relates to speech and attention because scents stimulate our brain and cause us to pay attention to certain things in our environment. It also related odorant recognition to speech recognition. Our brain can recognize certain stimulants and put words to those objects, movements or people, however, with scents we cannot put words to what we are smelling but recognize that we know the odor.

olfaction, odor, odorant, olfactory cleft, olfactory epithelium, supporting cells, basal cells, olfactory sensory neurons, olfactory receptors, anosmia, cross adaption, receptor adaption, tip-of-the-nose phenomenon

As humans we have two chemical detection systems: one is for molecules floating in the air, the other is for molecules we put in our mouths. The big fancy words for smell and taste are olfaction (smell) and gestation (taste). When talking about smell, a word that is often used is odor. An order is a particular quality of the smell of something. One important part in the nose when talking about smell is the olfactory cleft. This is a part in the back of the nose into which air flows, the main olfactory epithelium is located here. The olfactory epithelium detects odors. There are three types of cells in the olfactory epithelium, these are called the supporting cells. These cells perform supportive functions. There are also three other types of cells in the olfactory epithelium which are called the basal cells. Another important part in the physiology of smell is the olfactory sensory neurons (OSNs). The receptor site for odorant molecules are on the cilia. The place where odorant molecules bind is called the olfactory receptor (OR). Next, the cribrifom is a bony structure that separates the nose from the brain. This is where the olfactory neurons pass through. Olfactory nerves and olfactory bulb are both important in the study of smell physiology. Olfactory bulbs are where olfactory information is first processed. There are two Olfactory bulbs, they are in each of the brain hemispheres and they correspond to each nostril. The mitral cells are the main projective output in the olfactory bulbs. The secondary class of output cells are the tufted cells. The brain region that processes smell is the olfactory cortex. The Olfactory cortex consists of the piriform cortex, the amygalda-hippocampal complex, and the enthrhinal complex. Another important aspect of smell when talking about the physiology of it is the genetic basis olfactory receptors.
This chapter also talks about the psychophysics of smell. So now I will talk about olfactory psychophysics. First, we must talk about identification. The tip-of-the-nose phenomenon is very cool. This is the inability to name an odorant, even though it is very familiar. Next, the book goes on to talk about adaptation. When talking about adaptation it is important to note G protein-coupled receptors (GPCRs). GPRCs are the class of receptors that are present on the surface of olfactory sensory neurons. Receptor adaptation is the biochemical phenomenon that occurs after continuous exposure to an odorant where the receptors stop responding to the odorant and detection ceases. Cross-adaptation is the successive reduction in detection of an odorant following exposure to another odorant. Cognitive habitation is also part of the psychophysics of smell. This is the psychological process by which, after long term exposure to an odorant, one is no longer able to detect that odorant or has very diminished detection ability. I also found this to be very interesting.
In this chapter I found anosmia to be very interesting. This is the inability to smell. This call result from sinus illness or head trauma.