Olfaction 1 What is the function of olfaction Approach avoidance Additional social role pheromones 2 Dogs have more olfactory receptor neurons that humans and rats have more types of olfactory receptors than humans What are the functional consequences of these differences Discrimination differentiation between scents Lower threshold for scents which leads to better detection 3 What makes something an odorant Are there compounds that should be odorants but we cannot smell Small Volatile able to float in the air Hydrophobic Not all molecules that should smell to humans according to above criteria do smell to us we do not have receptors for them evolutionarily never in a small room where it would be dangerous to be with them Natural gas methane CO 4 Anatomy of the olfactory system What are turbinates What is the olfactory epithelium what types of cells does it contain Olfactory bulb Cribriform plate Glomeruli Olfactory nerve 1 Turbinates ridges that add turbulence to incoming air to send some through the olfactory cleft and onto the olfactory epithelium Olfactory Epithelium 2 75 inches up from nostril just below cribriform plate under frontal lobes 3 types of cells Supporting cells Basal cells stem cells that mature to new olfactory sensory neurons Olfactory Sensory Neurons expresses 1 type of receptor protein about 20 million OSNs Cribriform plate bony structure that OSNs project through to get to glomeruli Glomeruli synapses between axons of OSNs and dendrites of mitral and tufted cells Each Glomeruli gest input from one type of olfactory receptors 20 million OSNs 350 different types of receptors Different types of receptors throughout olfactory epithelium all same receptors converge to one glomeruli Olfactory nerve OSNs project through cribriform plate to glomeruli clusters of neurons in olfactory bulb these axons constitute the olfactory nerve ipsilateral projection 5 Understand the anatomy of the olfactory receptor cells in olfactory epithelium cilia dendrites extend into mucosa and contain receptors axon travels thru cribriform plate as part of olfactory nerve and ends in olfactory bulb Each sensory neuron has only one type of olfactory receptor protein Receptor proteins are on cilia of receptor cells Receptor proteins are metabotropic 2nd messenger opens channels that flux Na and Ca2 Also open a Cl channel lots of Cl inside these cells so parts of depolarization caused by Cl efflux 2 6 How is the olfactory information organized in the olfactory bulb especially w regard to glomeruli 300 400 functional olfactory receptor types but we discriminate thousands of odors Each odorant molecule has features that could stimulate multiple receptors Each receptor has multiple feature detectors 20 million OSNs 350 receptor types 1 glomeruli Blue OSNs all converge to the blue glomerulus red to red etc 7 What is the projection neuron within the glomerulus that receives info from the olfactory nerve and sends info to the cortex What parts of cortex get olfactory info Where else in the brain does olfactory information go and what are the roles of each of those regions Olfactory bulbs mitral cells project information directly to entorhinal cortex piriform cortex amygdala Glomeruli in olfactory bulb getting information from olfactory nerves sending axons to the amygdala and cortex tissues surrounding it piriform and tissue around hippocampus and pre frontal cortex and to hypothalamus 8 What is shape pattern theory Lock receptor and key odorant Odorant molecules have different shapes Olfactory receptors have different shapes Different scents as a function of odorant shape or OR shape fit activate different arrays of olfactory receptors in the epithelium 3 Various arrays produce specific firing patterns of neurons in OB a pattern is generated across the glomeruli which determines what scent we perceive So olfactory perception is based on cross fiber patterning The overall pattern of activity in the OB and then olfactory cortex determines the odor we perceive 9 Do we use labeled line or cross fiber patterning to identify odors Understand why Cross fiber patterning odorant molecules can activate multiple receptor cites and to multiple odorants never 1 1 always multiple odorants to multiple glomeruli There are different patterns of activation for scent like roses versus rotting fish pattern path is different not the only thing that makes response but glomeruli respond to preference and experience 10 What is anosmia and what can cause it What is specific anosmia and what is its most common cause Anosmia inability to smell Whip lash type accident sheer axons of olfactory receptor cells can grow back If cribriform plate is fractured by blow to head it could scar and axons cannot regrow Specific anosmia the inability to smell a specific compound amid otherwise normal smell perception Usually to steroid musk compounds Usually genetic 11 What are some differences between men and women in olfaction 4 Women detect odors more readily than men have lower thresholds than men especially when ovulating Women of child bearing age sensitize to odors until they smell them in very faint amounts Odor most important to women than men in choosing partners 12 How why do olfactory thresholds increase with age Ability to replace OSNs decreases with age 13 What are some functional consequences of the ipsilateral projection of the olfactory system together with the lateralization of language and emotion check out web essay 13 1 Olfaction also appears to be preferentially lateralized to the right hemisphere The fact that both olfaction and emotion are processed in the right hemisphere while language is processed in the left has some important consequences When you sniff an odor for example coconut extract you will evaluate it as more pleasant more emotionally positive if you sniff it through your right nostril than if you sniff it through your left nostril However you will be more likely to correctly name the odor as being coconut if you sniff it through your left nostril rather than your right In other words our emotional responses to odors are heightened by smelling with our right hemisphere where emotion is more dominant and our verbal labeling abilities with odors are improved by smelling with the left hemisphere where language is more dominant 14 What is adaptation Physiologically speaking why does it occur Is there a psychological effect on adaptation Adaptation stop perceiving an odorant while still in its presence
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