Perception Final Exam Study Guide Chapter 14 Olfactory Physiology Basic original purpose to take in some substances and avoid others food toxins Detecting chemicals crucial Systems to detect analyze environmental molecules were first senses Olfaction chemicals in air Gustation chemicals in mouth Trigeminal system enables us to feel gustatory and olfactory experiences burning and cooling Odors and Odorants chocolate odor Odors translation of chemical stimulus into smell sensation cake has a Odorant molecule defined by physicochemical characteristics capable of being translated by NS into perception of smell given odorant of methyl salicylate odor of wintergreen o Must be volatile float through air o Small less than 5 8 x 10 22 g o Hydrophobic repel water Cant smell components that make up air nitrogen oxygen or carbon monoxide The Human Olfactory Apparatus Nose primary function to filter warm and humidify air Inside has small ridges turbinates that add turbulence and cause puff of breath to rise pass olfactory cleft and settle on epithelium Olfactory cleft narrow space at back of nose into which air flows and where olfactory epithelium is located Olfactory epithelium secretory mucous membrane whose function is to detect odorants in inhaled air on both sides of upper portion of nasal cavity o Retina of nose o 3 cell types olfactory sensory neurons basal cells supporting cells Supporting cell provide metabolic and physical support for OSN Basal cell precursor cells to OSN OSN small neurons beneath watery mucous in epithelium cilia on dendrites have receptor sites for odorant molecules Cilium hairlike protrusions on dendrites of OSN receptors for odorant molecules first structures involved in transduction Olfactory receptors region of cilia where odorant molecules bind To initiate action potential 7 8 odorant molecules bind to receptor takes 40 nerve impulses for smell to be reported 20 million OSNs more sensory neurons in any system besides vision Nasal dominance asymmetry characterizing intake of air by two nostrils differing sensitivity between them alternates nostrils throughout the day no predictability about when nostrils alternate Cribriform plate axons pass through these to enter the brain bony structure riddled with holes at level of eyebrows separates nose from brain Anosmia total inability to smell resulting from sinus illness or head trauma Stem cells can form new OSNs all die and regenerate every 28 days Fractured plates scar over and prevent new OSN axons from passing Medicine used to treat high blood pressure or elevated cholesterol cause smell 2nd common cause sinonasal disease loss 3 born anosmic Connection between depression and sense of smell Neurobiological connection between olfactory and emotional processing enables bidirectional interaction 1 in 100 suffer from anosmia Olfactory loss can signal Parkinson s and Alzheimer s OSN axons bundle and form olfactory nerve enter extension of brain called Nerve first pair cranial nerves conducts impulses from olfactory epithelia in olfactory bulb nose to olfactory bulbs Olfactory bulb blueberry sized extension of brain above nose olfactory information first processed 2 bulbs one in each hemisphere correspond to L R nostrils Olfaction ipsilateral right bulb gets info from right nostril Glomeruli any spherical conglomerates containing incoming axons of olfactory sensory neurons each OSN converges onto two glomeruli o Specific pattern interpreted as indicating specific odor o Aversion pattern of activity produced by scent looks different o No fixed code for odor perception personal experience determines processing o Mitral cell any of main projective output neurons in olfactory bulb o Tufted cell secondary class of output neurons in olfactory bulb Nerve cells coordinate info from glomeruli for further processing distribution to higher brain centers o Olfactory tract formed by axons of mitral and tufted cells bundles within olfactory bulb that send odor information to primary olfactory cortex o Primary olfactory cortex piriform cortex neural area where olfactory info first processed amygdala parahippocampal gyrus interconnected areas o Entorhinal cortex phylogenetically old cortical region provides major sensory association input into hippocampus receives direct projections from olfactory regions o Humans have 6000 glomeruli Limbic system group of neural structures that includes olfactory cortex amygdala hippocampus piriform cortex entorhinal cortex involved in emotion and memory olfaction connected also Olfactory cells make direct contact with brain drugs can be inhaled OSN axons slowest and thinnest in body takes long to perceive smell The Genetic Basis of Olfactory Receptors Between 1000 2000 olfactory receptor genes each codes for single OR Pseudogenes present on chromosomes but proteins never get produced More copies of specific receptor more sensitive to certain odorants More receptors leads to less pleasant experience of scent No innate responses with sense of smell The Feel of Scent pain and temperature Odors stimulate somatosensory system through polymodal nociceptors touch Menthol cool Ammonia burning Trigeminal nerve 5th pair cranial nerves that transmit information about feel of odorant as well as pain and irritation sensations High levels trigeminal stimulation munching habanero peppers produces severe burning Smelling salts revive us because of trigeminal activation From Chemicals to Smells No fully comprehensive theory of how we perceive scents Theories of Olfactory Perception Match between shapes of odorants and odor receptors Shape pattern theory dominant biochemical theory different scents as function of fit between odorant shape to OR shape activate different arrays of olfactory receptors producing specific firing patterns of neurons in olfactory bulb which determine scent we perceive One odorant binds to several receptors and one receptor binds several Different scents activate different arrays of olfactory receptors producing specific Vibration theory alternative every odorant has vibrational frequency molecules that produce same frequencies smell same Specific anosmia inability to smell one compound amid normal smell odorants firing patterns of neurons perception completely different Stereoisomers molecules that are mirror image rotations of one another smell o Vibration is same but smell is different The Importance of Patterns Discriminate thousands of odors but genes code for 1000 olfactory receptors