Description This week we will examine the chemical sense of smell (olfaction) and taste. This is a two-part discussion question (part one pertaining to olfaction and part two pertaining to taste) and both parts must be answered in order to receive full credit. After viewing the material for this week as outlined in the syllabus, discuss the components of the olfactory system: the olfactory receptors, the olfactory sensory neurons, the olfactory bulb and the cortex. Then, discuss what kinds of evidence support the idea that different people may have different taste experiences. What mechanisms might be responsible for these differences? Lastly, explain the role of culture in the development of smell and taste and provide two examples of how culture could account for variation in perception. Minimum 300 words answer Classmate #1: Olfactory receptor, also known as the scent receptor, a protein that binds molecules of odor and plays a key role in smell detection (olfaction). Such receptors are commonly found in arthropods, vertebrates of the earth, fish and other animals. Receptors are located on olfactory receptor cells, which are present in very many (millions) “terrestrial vertebrates, including humans, and which form an olfactory epithelial in a small area on the back of the nasal cavity. Growing receptor cell has a single external process extending to the epithelium surface, leading to a long, slender extension called cilia. Cilia are covered by the nasal cavity mucus which facilitates the detection and reaction of olfactory receptors to smell molecules. The olfactory receptors are mounted on exciting structures such as antennas in arthropods. The olfactory receptor proteins within the cell membrane are positioned so that one end is outside the cell and the other finishes in the cells. It allows a chemical outside the cell to interact with and create changes in the cellular system without reaching the cell, for example, by an odorant molecule. A chain of amino acids binds the external and internal ends of receptor proteins involved in smell. The chain is said to have seven transmembrane domains because of the thickness of the cell membrane seven times. The amino acid sequence of these proteins is important. It is believed that stimulation takes place when a molecule with a specific form fit in the receptor molecule in a corresponding’ box,’ as the key fits into a lock. A change in the shape of the pocket in a single amino acid can thus modify the chemical in the pocket. One olfactory receptor protein in rats, for example, induces a higher reaction within the recipient cell when dealing with alcohol called octanol (eight carbon atoms) than with alcohol known as heptanol (seven carbon atoms). Moving one amino acid, supposed to contribute to the shape of a pocket from the valine to the isoleucine in the fifth transmembrane region, changes the receptor protein in a way that produces the greatest effect instead of octanol. The analogous receptor is normally in this form in mice, which causes greater reaction than octanol to heptanol. This shows how important amino acid molecules are to determine receptor cell specificity. The peripheral olfactory system consists mainly of the nasal cavity, ethmoid bone, and olfactory epithet (thin-tap tissue layers that line the nasal cavity). The olfactory system consists of Mucus membranes, olfactory glands, olfactory neurons, and olfactory nerve fibers are the main elements in the layers of epithelial tissue. Olfactory stimuli disperse the action potential of an axon. Sensory olfactory neurons detect odorous molecules dissolving in molecules and transmit odor information to the brain during a sensory transduction process. Cilia (small hair) in olfactory neurons containing olfactory molecules that bind to molecules of odor, leading to electric response that spreads to olfactory nerve fibers at the back via the sensory neuron. Olfactory nerves and fibers transmit odor information from the peripheral olfactory system to the central olfactory brain system that is separated from the epithelium by the ethmoid bone cribriform. Olfactory nerve fibers coming from the epithelium cross the caliphal platform linking the epithelium with an olfactory bulb’s brain limbic system. Olfaction system data the main olfactory bulb transmits a pulse to both mitral and tufted cells that aid in determining odor levels based on the time of certain fire neuronal clusters. Such cells often notice differences between very similar odors and use these data to help identify them later. With low mitral fire levels and easy to inhibit with nearby cells, the tufts are different, and they have high firing rates and are harder to inhibit. The smell of tuber binds to a wide range of areas including the amygdala, thalamus, hypothalamus, hippocampus, brain stem, retina, auditory cortex, and olfaction. It is oversimplified in stating that: controls to ensure odor signals came from actual odors instead of villi irritation, regulates engine activity (mostly social and stereotypical) produced by smells and incorporates the sensory auditory and olfactory information in order to complete the tasks mentioned above and plays a role in transmitting positive signals to the recompense sensors. The amygdala (in olfaction) processes pheromone, allomone and kairomone signals, respectively, where the emissary is affected, and the receptor benefitted from the same species, cross-species, and cross-species. This procedure is secondary because of the formation of the cerebrum and therefore largely unnoticed in human interactions. Allomones include floral scents, natural herbicides and natural toxic chemicals from plants. The knowledge for these processes comes indirectly through the smelling bulb from the vomeronasal organ. The key signals of the olfactory bulb in the amygdala are used to associate smells with names and to distinguish scent variations. Classmate #2: Olfaction is our sense of smell. The olfactory system includes many parts and functions. Olfactory Receptors are often called smell receptors. They are able to bind odor molecules that contribute to our sense of smell. The receptors give us the ability to taste five different tastes; sweet, salty, umami, sour, and bitter. There are more than 300 different types of receptors and humans have about 10 million. The olfactory epithelium is clustered in the back of the nasal cavity. The epithelium works with slim additions called cilia. Cilia are covered in mucus in the nasal cavity that helps in the discovery of odor by the olfactory receptors. Olfactory Sensory Neurons are defined as the receptor neurons for odor discovery. These sensory neurons are unique to the genes, neuronal differentiation, and physiological properties. The sensory neurons can sense chemical stimuli found in the environment. The chemical stimuli signal action potentials that move to the olfactory bulbs by way of the olfactory nerve then on to the central nervous system. Olfactory Bulb is a structure found on the bottom of the cerebral hemisphere. It is attached to the cerebral hemisphere the olfactory stalk or peduncle. The olfactory bulb has many kinds of cells called mitral cells, granule cells, tufted relay neurons and periglomerular neurons. The cells recognize olfactory information and then take it to the olfactory cortex for interpretation. Olfactory Cortex is part of the front part of the brain that gets input from the olfactory bulb through the olfactory tract and parts of the olfactory tubercle, amygdala, and entorhinal cortex. This cortex is important in how we perceive an odor we acquire from our nose. The fact that some people can eat spicy foods and some cannot or that some like bitter or sour food and others do not shows that we taste and perceive tastes differently. How our brain perceives these tastes would be responsible for these differences. Also, each of us is effected by our cultures and how growing up with certain smells and tastes can either make these items normal to us and enjoyable or abnormal and disliked. An example of this would be Eskimo children growing up in Alaska that find eating whale and wild life daily. This may not be appealing to those who have not been raised with this as a cultural norm. Another example is spicy foods; those raised on spicy foods are not affected by it but, those not raised on spicy foods many times will not be able to eat them. Classmate #3: Hello Class, Happy Wednesday, I hope everyone is having a great week. We are almost done with this course so let’s continue pushing forward. This week we focused on olfactory system, and how smell and taste work. The olfactory receptors can also be known as the smell receptor or odorant receptors. They work by detecting odorants and sending impulses to the brain so the brain can identify the smell. Olfactory sensory neurons are responsible for facilitating this process. They are located in nasal epithelium, and they carry the information to the central nervous system. An interesting fact that I read was that we have anywhere between 10-20 million olfactory receptor neurons. Each receptor reaches to the surface of the epithelium and is connected to cilia. Cilia also plays an important function, since cilia is covered by mucus that’s in our nasal cavity. Cilia helps detect the odor molecules. The next part of the olfactory system is the olfactory bulb, and its functionality is to receive the neural information about the odors that were detected in the nasal cavity. The olfactory bulb is located on the bottom, or inferior side of the cerebral hemisphere. This part is connected to the last section in this discussion, which is the olfactory cortex. The olfactory cortex receives the signals from the olfactory bulb and is made up of several parts. The piriform cortex, olfactory tubercle, anterior olfactory nucleus, and part of amygdala and entorhinal cortex. (Olfactory System, n.d.). Like most of the systems we have learned over the past several weeks, this sense has different components, and moving pieces that allow us to taste, and smell. People have different taste experiences depending on different things like what they grew up eating. This can begin as early as when babies are in the womb. (Reed, D. R., Tanaka, T., & McDaniel, A. H, 2006). For example, growing up in a Hispanic home, we ate a lot tortillas, used a lot of lime, salsa, and other spicy food. However, my husband who is African-American can’t stand the smell of some of the hot sauce that I use, or how I can even put it on things like chips, fruit, or popcorn. He has things that he grew up eating that I don’t enjoys. I think for this reason it’s important to start setting the expectations while a child is young, to get used to eating fruits and vegetables, not just processed foods like chicken nuggets, fries, and other foods that might not provide nutritional value. Hope everyone has a great week, and good luck this week! Minimum 200 words answer to each
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