Chapter 13I Olfaction A. Perceiving Odors1. odorants are molecules that olfactory receptors recognize and respond to by producing neural signals that the brain represents as perceptions of different odors2. odors are primarily produced by organic substances and all terrestrial plants at normal environmental temperaturesB. Odor Detection1. the concentration of an odorants factors into the detection a. concentration is measured in the number of odorant molecules per 1 million moleculesb. concentration depends on source, location, and confinementc. concentration also effects the identification of odor2. perceived intensity generally increased as the concentration increasesC. Thresholds1. strength of an odor is described as the detection threshold2. concentration must change substantially before people notice a difference in the intensityD. Identifying and Discriminating Odors1. the ability to identify odors as well as the ability to discriminate between similar odors depends not just on context but also on training and experience2. training and specialization can improve ability to identify odors, but not necessarily in detection3. most relations between smells and memory are formed in the earliest decade of lifeII Olfactory ImpairmentsA. Age1. olfactory performance declines with ages, just as all other senses2. dramatic decrease typical around age 70, stronger in men3. anosmia is the loss of smella. smokers at high risks, but can recover lost abilityB. Genetic Mutation1. a genetic mutation that leads to an inability to perceive pain can also lead to anosmia C. Injury1. injury to the anatomical structures that support olfaction can cause anosmia2. when receptor neurons are damaged they degenerate over a period of several days3. stem cells in the nose can become new receptors and reconnect the nose to the brainIII Molecular Aspects of OdorsA. cross Adaptation1. olfaction is especially sensitive to change, but once identified and responded to the scent’s presence becomes less important2. repeated exposure to an odor reduces sensitivity to it, but it can also reduce sensitivity to other similar odors, known as cross adaptation3. in an experiment with rats, investigation time was greatest for test odorants that were most dissimilar to the adapted odoranta. the study suggests that the physical property of molecules is atleast partly responsible for perceptual similarity4. ORNs have only one type of receptor on their ciliaCheck Your Understanding: What are two factors that determine whether a particular type of molecule willevoke a response in a normally functioning olfactory system? 1. whether it’s a recognizable odor molecule(lipid soluble) and whether the concentration is high enough to reach or exceed the detection thresholdIf two odorants are present at equal concentrations, which is more likely to be perceived, the odor with thehigher detection threshold or the odor with the lower detection threshold? The odor with the lower detection threshold.T/F: People who smoke heavily for 10 years or more typically suffer severe permanent olfactory impairments. False, damage is repaired. Olfaction receptors can regenerate from stem cells in the nasal cavity.Which choices will make the following statement false: training and specialization help people (detect,identify,remember,discriminate) odors. (1)Detection doesn’t improve with training and (2)Remember an odor is possible without training.B. Neural Basis of Odor Perception1. turbinates, bony convolutions of tissue, disperse the air evenly throughout each nasal cavity2. nasal passages join at the pharynx3. transduction of odorant molecules into neural signals is carried out by olfactory receptor neurons embedded in the olfactory epithelium located a few centimeters behind each eyea. each ORN dies after a few weeks and is replaced by a new ORN (generated by basal cells)b. bowman’s glands (also in epithelium) secrete mucus to wash out odorant molecules from the epitheliumc. mucus also provides protection from irritants and against harmful microorganismsC. Transduction1. each ORN has hairlike cilia projecting into the mucus, each covered with olfactory receptors that bind with odorant molecules that dissolve into the mucus2. olfactory receptors have GPCR ion channels (like vision) 3. when the membrane opens, positive calcium and sodium ions flow in4. depolarization generates action potentials5. ORN axons form olfactory nerve that travel to the olfactory bulb through a grid oftiny holes in the cribriform plate6. ORN axons enter the glomeruli where they make synapses with the dendrites of two types of relay neuronsa. mitral cells and tufted cells form the olfactory tractD. Olfactory Receptors1. humans have approximately 350 receptors for olfaction2. each ORN has only one type of receptor on its cilia, so there are also about 350 types of ORNS3. humans have about 10-20k of each type of ORNs who send their axons to about5000 glomeruli in the olfactory bulbE. Coding 1. an estimated 4% of human DNA is devoted to coding for the 350 olfactory receptors2. olfaction operates on a population code similar to that of visiona. based on relations between 350 receptors instead of 33. the pattern of ORN responses(the particular subset of ORN types activated and the relative strength of their responses) determines how an odorant smells4. responses can be quite different for molecules with similar structureF. Upper Processing1. the piriform cortex is consider the primary olfactory cortexa. dedicated purely to olfactionb. anterior piriform cortex produces representations of the chemical structure of odorant moleculesc. posterior piriform cortex produces representations of the quality of an odor as a whole, regardless of whether the odor is simple or complex(activity in OFC and amygdala didnt reflect differences)d. evidence of the APC PPC distinction found using fMRI information2.also involves amygdala and entorhinal cortex (involved in other nonolfactory functions)a. amygdala crucial in emotional responsesb. most effectively activated by pleasant and unpleasant smells, as opposed to visual or auditory informationCheck Your Understanding: Which choices match up to make two different correct statements: ([A] olfactory receptor neurons [B] mitral cells and tufted cells) form the ([C] olfactory tract [D] olfactory nerve).A-D and B-CWhy is the piriform cortex considered the primary olfactory cortex and how do the APC and PPC differ in the kind of olfactory