DOCSLIB.ORG

The Olfactory System and Its Disorders

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text

Load more

The Olfactory System and Its Disorders Richard L. Doty, Ph.D.1 ABSTRACT The sense of smell is greatly underappreciated, despite the fact that it monitors the intake of airborne agents into the human respiratory system and determines to a large degree the flavor and palatability of foods and beverages. In addition to enhancing quality of life, this primary sensory system warns of spoiled foods, leaking natural gas, polluted air and smoke, and mediates basic elements of communication (e.g., mother–infant interactions). It is now apparent that smell dysfunction is among the first clinical signs of such neurodegenerative diseases as Alzheimer’s disease and sporadic Parkinson’s disease. In this brief article, the author reviews the anatomy and physiology of this primary sensory system, means of assessing its function, and major diseases and disorders with which it is intimately associated. KEYWORDS: Smell, olfaction, anosmia, dysosmia, Alzheimer’s disease, Parkinson’s disease, aging Although neglected by the medical community enter the nasal pharynx during deglutition.9 These at large, olfaction is critically important for safety, nutri- sensations disappear when the olfactory epithelium is tional status, and quality of life; its dysfunction is now markedly damaged, leaving intact only somatosensory known to be among the earliest ‘‘preclinical’’ signs of sensations and the perception of the primary taste qual- Alzheimer’s disease (AD) and sporadic Parkinson’s dis- ities of sweet, sour, salty, bitter, metallic, and umami ease (PD).1–6 Among 750 consecutive patients present- (monosodium glutamate–like). Whole-mouth taste func- ing to the University of Pennsylvania Smell and Taste tion is much more resilient to pathologic or trauma- Center with chemosensory complaints, 68% experienced related alterations than is smell function, in large part an altered quality of life, 46% changes in appetite or because of the redundant innervation of the taste buds body weight, and 56% adverse influences on daily from several cranial nerves (i.e., CN VII, IX, and X).7 living or psychological well-being.7 In another study of In this article the anatomy and physiology of the 445 patients with complaints of chemosensory disturb- olfactory system is reviewed, as well as means for assess- ance, at least one hazardous event, such as food poison- ing its function and disorders in which it is intimately ing or failure to detect fire or leaking natural gas, was involved. Emphasis is placed on disorders commonly reported by 45.2% of those with anosmia, 34.1% of those encountered by the practicing neurologist. with severe hyposmia, 32.8% of those with moderate hyposmia, 24.2% of those with mild hyposmia, and This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. 19.0% of those with normal olfactory function.8 ANATOMY AND PHYSIOLOGY Most complaints of decreased ‘‘taste’’ function actually reflect decreased smell function.7 Such flavors Sensory Receptors and Primary Neurons as coffee, chocolate, vanilla, strawberry, pizza, licorice, The peripheral elements of the olfactory system consist steak sauce, root beer, and cola are dependent upon of 6 million bipolar receptor cells whose cell bodies, stimulation of cranial nerve (CN) I from volatiles that dendrites, and initial axon segments are located within 1Smell and Taste Center, University of Pennsylvania School of Disorders of the Cranial Nerves; Guest Editor, William W. Campbell, Medicine, Philadelphia, Pennsylvania. M.D., M.S.H.A. Address for correspondence and reprint requests: Richard L. Doty, Semin Neurol 2009;29:74–81. Copyright # 2009 by Thieme Ph.D., Professor and Director, Smell and Taste Center, University of Medical Publishers, Inc., 333 Seventh Avenue, New York, NY Pennsylvania School of Medicine, 5 Ravdin Pavilion, 3400 Spruce 10001, USA. Tel: +1(212) 584-4662. Street, Philadelphia, PA 19104 (e-mail: [email protected]). DOI 10.1055/s-0028-1124025. ISSN 0271-8235. 74 THE OLFACTORY SYSTEM AND ITS DISORDERS/DOTY 75 the olfactory neuroepithelium in the roof of the nasal ify and degrade odorants, and transport some molecules chamber.10 This pseudostratified columnar epithelium is across the epithelium. However, most of the mucus that supported by a highly vascularized lamina propria cover- covers the surface of the olfactory epithelium comes from ing the cribriform plate, the superior septum, and sectors Bowman’s glands, specialized glands found only within of both the superior and middle turbinates.11 The the olfactory epithelium. Among other cell types within receptor cell axons project through the cribriform plate this epithelium are basal stem cells (the precursors of all of the ethmoid bone and synapse within the glomerular of the main types of cells of the epithelium) and the layer of the olfactory bulb after forming into bundles— poorly understood microvillar cells, which number the olfactory fila. Receptor-bearing cilia, numbering 600,000 in humans and send tufts of microvilli into from 3 to 50 per cell, project from the dendritic ends the nasal mucus.10 of the receptor cells into the overlying mucus, in some cases radiating over 30 mm. In the human, the surface area of the cilia is 25 mm2.12 Olfactory Bulbs and Their Projections The bipolar receptor neurons are unique in several Each ovoid olfactory bulb is located at the base of the ways. First, they can regenerate from basal cells after frontal lobe overlying the cribriform plate of the ethmoid being damaged. Second, each cell serves as both a bone. The olfactory bulbs are composed of neurons, receptor cell and a first-order neuron, projecting an afferent and efferent nerve fibers, multiple interneurons, axon directly from the nasal cavity into the brain without microglia, astrocytes, and blood vessels, all surrounded an intervening synapse. Their rather direct exposure to by a thin layer of pia-arachnoid cells.19 The bulb’s the external environment, along with their large surface cellular elements are arranged in six concentric layers: area and minimal xenobiotic-metabolizing capacity, the olfactory nerve layer, the glomerular layer, the make them a primary route of invasion into the brain external plexiform layer, the mitral cell layer, the internal of several xenobiotic agents. Indeed, many neurovirulent plexiform layer, and the granule cell layer. The latter viruses are capable of penetrating the brain via the layer makes up about half the volume of the entire bulb. olfactory receptor cells.13 Finally, such cells are highly The receptor cell axons synapse within the spher- specialized, individually expressing receptors that re- ical olfactory bulb glomeruli, which are arranged in spond to only certain elements of odorant ligands.14 single or double layers. These structures number in the The initial step in olfactory transduction is the thousands in younger persons and are a defining feature movement of odorants from the air phase of the nasal of the olfactory system. With age, however, the number cavity into the aqueous phase of the olfactory mucus. and integrity of the glomeruli greatly decrease, being Odorants, most of which are hydrophobic, then diffuse nearly absent in elderly persons.20 The development and or are transported through the aqueous medium to maintenance of the glomeruli depend on trophic influ- olfactory receptor proteins of the cilia, ultimately induc- ences exerted by the receptor cells. Because a given ing action potentials in the receptor cells.15 Although receptor cell projects to only one or two glomeruli, the several odorants stimulate free nerve endings from CN V glomeruli are, in effect, functional representations of the and some other cranial nerves distributed in the nasal receptor types.14 mucosa, nasal pharynx, or oral cavity, such stimulation The main second-order neurons, which are the primarily involves somatosensory sensations of the primary output neurons of the bulb, are the mitral and ‘‘common chemical sense,’’ such as warmth, coolness, tufted cells. The apical dendrites of these cells are pungency, and irritation.16 influenced not only by the olfactory nerve terminals, There is marked genetic diversity in olfactory but also by interneurons and centrifugal fibers, most of receptors. A large multigene rodent family of 1000 which are GABAergic or dopaminergic.21 Several bulbar genes appears to code for odorant receptor proteins with interneurons, including the granule cells, are replaced by This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited. seven transmembrane domains.17 In humans, more than progenitors germinating within the subventricular zone half of this receptor gene family are pseudogenes, of the brain. These cells migrate along the rostral indicating that the number of functional receptors is migratory stream to the olfactory bulb.22 less than 500.18 Even though each receptor cell expresses only one type of olfactory receptor, such cells respond to a wide range of odorants. However, a given receptor, Olfactory Cortex though a ‘‘generalist,’’ does not respond to all stimuli The mitral and tufted cell axons leave the bulb via the to which another receptor responds, thereby allowing for lateral olfactory tract to synapse on structures collectively cross-neuron quality coding.14 termed the primary olfactory cortex, including the ante- The olfactory receptors cells are physically iso- rior olfactory nucleus (AON), the piriform cortex, the lated from one another within the olfactory neuroepi- anterior cortical
Recommended publications
  • Born Granule Cells During Implicit Versus Explicit Olfactory Learning

    Born Granule Cells During Implicit Versus Explicit Olfactory Learning

    RESEARCH ARTICLE Opposite regulation of inhibition by adult- born granule cells during implicit versus explicit olfactory learning Nathalie Mandairon1*, Nicola Kuczewski1, Florence Kermen1, Je´ re´ my Forest1, Maellie Midroit1, Marion Richard1, Marc Thevenet1, Joelle Sacquet1, Christiane Linster2,3, Anne Didier1 1Lyon Neuroscience Research Center, Neuroplasticity and Neuropathology of Olfactory Perception Team, CNRS UMR 5292, INSERM U1028, Universite´ de Lyon, Lyon, France; 2Computational Physiology Lab, Cornell University, Ithaca, United States; 3Department of Neurobiology and Behavior, Cornell University, Ithaca, United States Abstract Both passive exposure and active learning through reinforcement enhance fine sensory discrimination abilities. In the olfactory system, this enhancement is thought to occur partially through the integration of adult-born inhibitory interneurons resulting in a refinement of the representation of overlapping odorants. Here, we identify in mice a novel and unexpected dissociation between passive and active learning at the level of adult-born granule cells. Specifically, while both passive and active learning processes augment neurogenesis, adult-born cells differ in their morphology, functional coupling and thus their impact on olfactory bulb output. Morphological analysis, optogenetic stimulation of adult-born neurons and mitral cell recordings revealed that passive learning induces increased inhibitory action by adult-born neurons, probably resulting in more sparse and thus less overlapping odor representations. Conversely, after active learning inhibitory action is found to be diminished due to reduced connectivity. In this case, strengthened odor response might underlie enhanced discriminability. *For correspondence: DOI: https://doi.org/10.7554/eLife.34976.001 [email protected] Competing interests: The authors declare that no Introduction competing interests exist. Brain representations of the environment constantly evolve through learning mediated by different Funding: See page 13 plasticity mechanisms.
  • Chemoreception

    Chemoreception

    Senses 5 SENSES live version • discussion • edit lesson • comment • report an error enses are the physiological methods of perception. The senses and their operation, classification, Sand theory are overlapping topics studied by a variety of fields. Sense is a faculty by which outside stimuli are perceived. We experience reality through our senses. A sense is a faculty by which outside stimuli are perceived. Many neurologists disagree about how many senses there actually are due to a broad interpretation of the definition of a sense. Our senses are split into two different groups. Our Exteroceptors detect stimulation from the outsides of our body. For example smell,taste,and equilibrium. The Interoceptors receive stimulation from the inside of our bodies. For instance, blood pressure dropping, changes in the gluclose and Ph levels. Children are generally taught that there are five senses (sight, hearing, touch, smell, taste). However, it is generally agreed that there are at least seven different senses in humans, and a minimum of two more observed in other organisms. Sense can also differ from one person to the next. Take taste for an example, what may taste great to me will taste awful to someone else. This all has to do with how our brains interpret the stimuli that is given. Chemoreception The senses of Gustation (taste) and Olfaction (smell) fall under the category of Chemoreception. Specialized cells act as receptors for certain chemical compounds. As these compounds react with the receptors, an impulse is sent to the brain and is registered as a certain taste or smell. Gustation and Olfaction are chemical senses because the receptors they contain are sensitive to the molecules in the food we eat, along with the air we breath.
  • Understanding Sensory Processing: Looking at Children's Behavior Through the Lens of Sensory Processing

    Understanding Sensory Processing: Looking at Children's Behavior Through the Lens of Sensory Processing

    Understanding Sensory Processing: Looking at Children’s Behavior Through the Lens of Sensory Processing Communities of Practice in Autism September 24, 2009 Charlottesville, VA Dianne Koontz Lowman, Ed.D. Early Childhood Coordinator Region 5 T/TAC James Madison University MSC 9002 Harrisonburg, VA 22807 [email protected] ______________________________________________________________________________ Dianne Koontz Lowman/[email protected]/2008 Page 1 Looking at Children’s Behavior Through the Lens of Sensory Processing Do you know a child like this? Travis is constantly moving, pushing, or chewing on things. The collar of his shirt and coat are always wet from chewing. When talking to people, he tends to push up against you. Or do you know another child? Sierra does not like to be hugged or kissed by anyone. She gets upset with other children bump up against her. She doesn’t like socks with a heel or toe seam or any tags on clothes. Why is Travis always chewing? Why doesn’t Sierra liked to be touched? Why do children react differently to things around them? These children have different ways of reacting to the things around them, to sensations. Over the years, different terms (such as sensory integration) have been used to describe how children deal with the information they receive through their senses. Currently, the term being used to describe children who have difficulty dealing with input from their senses is sensory processing disorder. _____________________________________________________________________ Sensory Processing Disorder
  • Distinct Representations of Olfactory Information in Different Cortical Centres

    Distinct Representations of Olfactory Information in Different Cortical Centres

    LETTER doi:10.1038/nature09868 Distinct representations of olfactory information in different cortical centres Dara L. Sosulski1, Maria Lissitsyna Bloom1{, Tyler Cutforth1{, Richard Axel1 & Sandeep Robert Datta1{ Sensory information is transmitted to the brain where it must be behaviours, but is unlikely to specify innate behaviours. Rather, innate processed to translate stimulus features into appropriate beha- olfactory behaviours are likely to result from the activation of genetically vioural output. In the olfactory system, distributed neural activity determined, stereotyped neural circuits. We have therefore developed a in the nose is converted into a segregated map in the olfactory strategy to trace the projections from identified glomeruli in the olfactory bulb1–3. Here we investigate how this ordered representation is bulb to higher olfactory cortical centres. transformed in higher olfactory centres in mice. We have Mitral and tufted cells that innervate a single glomerulus were developed a tracing strategy to define the neural circuits that labelled by electroporation of tetramethylrhodamine (TMR)-dextran convey information from individual glomeruli in the olfactory under the guidance of a two-photon microscope. This technique labels bulb to the piriform cortex and the cortical amygdala. The spatial mitral and tufted cells that innervate a single glomerulus and is suffi- order in the bulb is discarded in the piriform cortex; axons from ciently robust to allow the identification of axon termini within mul- individual glomeruli project diffusely to the piriform without tiple higher order olfactory centres (Figs 1a–c, 2 and Supplementary apparent spatial preference. In the cortical amygdala, we observe Figs 1–4). Labelling of glomeruli in the olfactory bulbs of mice that broad patches of projections that are spatially stereotyped for indi- express GFP under the control of specific odorant receptor promoters vidual glomeruli.
  • Early Aging Effect on the Function of the Human Central Olfactory System

    Early Aging Effect on the Function of the Human Central Olfactory System

    Journals of Gerontology: Biological Sciences cite as: J Gerontol A Biol Sci Med Sci, 2017, Vol. 72, No. 8, 1007–1014 doi:10.1093/gerona/glw104 Advance Access publication June 11, 2016 Original Article Early Aging Effect on the Function of the Human Central Downloaded from https://academic.oup.com/biomedgerontology/article/72/8/1007/2629931 by guest on 27 September 2021 Olfactory System Choice Editor’s Jianli Wang,1 Xiaoyu Sun,1 and Qing X. Yang2 1Department of Radiology, Pennsylvania State University College of Medicine, Hershey. 2Departments of Radiology and Neurosurgery, Pennsylvania State University College of Medicine, Hershey. Address correspondence to Jianli Wang, MD, PhD, Department of Radiology, Pennsylvania State University College of Medicine, Hershey, PA 17033. E-mail: [email protected] Received November 23, 2015; Accepted April 27, 2016 Decision Editor: Rafael de Cabo, PhD Abstract During normal aging process, the smell function declines significantly, starting from the sixth decade of age. While it has been shown that activity in the central olfactory system of seniors responding to odor stimulation is significantly less than that of young people, no information of the aging effect on the functions of this system during normal adulthood and early aging has been gathered. In this study, we used functional magnetic resonance imaging to investigate the olfaction-related brain activity in the central olfactory structures of 43 healthy adult volunteers aged from 22 to 64 years. The participants’ smell identification function was negatively correlated with age (r = −.32, p = .037). Significant negative correlation was observed between age and the olfaction-related activities in the bilateral dorsolateral prefrontal cortex, left insular cortex, and left orbitofrontal cortex (p < .001, corrected with cluster size ≥28 voxels).
  • Quantitative Analysis of Axon Collaterals of Single Pyramidal Cells

    Quantitative Analysis of Axon Collaterals of Single Pyramidal Cells

    Yang et al. BMC Neurosci (2017) 18:25 DOI 10.1186/s12868-017-0342-7 BMC Neuroscience RESEARCH ARTICLE Open Access Quantitative analysis of axon collaterals of single pyramidal cells of the anterior piriform cortex of the guinea pig Junli Yang1,2*, Gerhard Litscher1,3* , Zhongren Sun1*, Qiang Tang1, Kiyoshi Kishi2, Satoko Oda2, Masaaki Takayanagi2, Zemin Sheng1,4, Yang Liu1, Wenhai Guo1, Ting Zhang1, Lu Wang1,3, Ingrid Gaischek3, Daniela Litscher3, Irmgard Th. Lippe5 and Masaru Kuroda2 Abstract Background: The role of the piriform cortex (PC) in olfactory information processing remains largely unknown. The anterior part of the piriform cortex (APC) has been the focus of cortical-level studies of olfactory coding, and asso- ciative processes have attracted considerable attention as an important part in odor discrimination and olfactory information processing. Associational connections of pyramidal cells in the guinea pig APC were studied by direct visualization of axons stained and quantitatively analyzed by intracellular biocytin injection in vivo. Results: The observations illustrated that axon collaterals of the individual cells were widely and spatially distrib- uted within the PC, and sometimes also showed a long associational projection to the olfactory bulb (OB). The data showed that long associational axons were both rostrally and caudally directed throughout the PC, and the intrinsic associational fibers of pyramidal cells in the APC are omnidirectional connections in the PC. Within the PC, associa- tional axons typically followed rather linear trajectories and irregular bouton distributions. Quantitative data of the axon collaterals of two pyramidal cells in the APC showed that the average length of axonal collaterals was 101 mm, out of which 79 mm (78% of total length) were distributed in the PC.
  • Treating Dysosmia, from Saline to Surgery

    Treating Dysosmia, from Saline to Surgery

    日鼻誌４７!：５１～５２，２００８ 特別講演２ TREATING DYSOSMIA, FROM SALINE TO SURGERY Donald A. Leopold, MD, FACS University of Nebraska Medical Center, Omaha, Nebraska, United States of America The sense of smell begins with airflow through the nose. The exact path of this airflow has only recently been investigated. Some of this data comes from models, both life size and enlarged models using measurements of airflow. Additional information comes from computerized airflow models of the nasal cavities. The neural pathways of olfaction begin with the olfactory receptors high in the nasal cavity. After transduction from the chemical to the electrical information, this information is transferred through the olfactory bulb and into the central brain. Patients typically present with one of three different types of dysosmia. The first is simply a decreased ability to perceive smells（hyposmia and anosmia）. The two remaining types of dysosmia relate to distortions of perceived smells. One of these（parosmia）is a distortion of smell odorants that are actually in the environment. The third type is theperceptionofanodorwhenthereisnoodorantintheenvironment（phantosmia or hallucination）. The clinical task of the physician seeing these patients is to decide on the etiology of the problem and to recom- mend therapy if possible. The clinical history is one of the best tools the clinician has, but the physical examination, sensory testing and imaging can also be helpful. Diagnostic categories for these patients are many, but the most com- mon include nasal inflammatory disease for about a third of these patients, the losses that occur after an upper respira- tory infection in about 25 percent of the patients and head trauma in about 15 percent of patients.
  • A Cellular Mechanism for Main and Accessory Olfactory Integration at the Medial Amygdala

    A Cellular Mechanism for Main and Accessory Olfactory Integration at the Medial Amygdala

    The Journal of Neuroscience, February 17, 2016 • 36(7):2083–2085 • 2083 Journal Club Editor’s Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see http://www.jneurosci.org/misc/ifa_features.shtml. A Cellular Mechanism for Main and Accessory Olfactory Integration at the Medial Amygdala E. Mae Guthman1* and XJorge Vera2* 1Neuroscience Graduate Program, University of Colorado Anschutz Medical Campus, Aurora, Colorado 80045, and 2Departamento de Biología, Universidad de Chile, Santiago, Chile, 7800003 Review of Keshavarzi et al. Many vertebrates rely on their accessory (Sua´rez et al., 2012). Chemical cues reach thalamus (Keshavarzi et al., 2014), and and main olfactory systems (AOS and the AOS at a specialized sensory epithe- predator odors activate neurons in both re- MOS, respectively) to interact with their lium located in the vomeronasal organ gions (Pe´rez-Go´mez et al., 2015). Ventro- environment. Shaped by evolution to (VNO), a close-ended tubular structure medial hypothalamic neuronal activity is drive the perception of volatile and non- connected to the nostrils and positioned both necessary (Kunwar et al., 2015) and volatile molecules (for review, see Sua´rez at the base of the medial septum. The sufficient (Kunwar et al., 2015; Pe´rez- et al., 2012), these sensory systems allow VNO is sequestered from airflow; thus, Go´mez et al., 2015) to drive defensive be- animals to react and learn about the the chemical cues must solubilize with na- haviors.
  • Taste and Smell Disorders in Clinical Neurology

    Taste and Smell Disorders in Clinical Neurology

    TASTE AND SMELL DISORDERS IN CLINICAL NEUROLOGY OUTLINE A. Anatomy and Physiology of the Taste and Smell System B. Quantifying Chemosensory Disturbances C. Common Neurological and Medical Disorders causing Primary Smell Impairment with Secondary Loss of Food Flavors a. Post Traumatic Anosmia b. Medications (prescribed & over the counter) c. Alcohol Abuse d. Neurodegenerative Disorders e. Multiple Sclerosis f. Migraine g. Chronic Medical Disorders (liver and kidney disease, thyroid deficiency, Diabetes). D. Common Neurological and Medical Disorders Causing a Primary Taste disorder with usually Normal Olfactory Function. a. Medications (prescribed and over the counter), b. Toxins (smoking and Radiation Treatments) c. Chronic medical Disorders ( Liver and Kidney Disease, Hypothyroidism, GERD, Diabetes,) d. Neurological Disorders( Bell’s Palsy, Stroke, MS,) e. Intubation during an emergency or for general anesthesia. E. Abnormal Smells and Tastes (Dysosmia and Dysgeusia): Diagnosis and Treatment F. Morbidity of Smell and Taste Impairment. G. Treatment of Smell and Taste Impairment (Education, Counseling ,Changes in Food Preparation) H. Role of Smell Testing in the Diagnosis of Neurodegenerative Disorders 1 BACKGROUND Disorders of taste and smell play a very important role in many neurological conditions such as; head trauma, facial and trigeminal nerve impairment, and many neurodegenerative disorders such as Alzheimer’s, Parkinson Disorders, Lewy Body Disease and Frontal Temporal Dementia. Impaired smell and taste impairs quality of life such as loss of food enjoyment, weight loss or weight gain, decreased appetite and safety concerns such as inability to smell smoke, gas, spoiled food and one’s body odor. Dysosmia and Dysgeusia are very unpleasant disorders that often accompany smell and taste impairments.
  • The Olfactory Bulb Theta Rhythm Follows All Frequencies of Diaphragmatic Respiration in the Freely Behaving Rat

    The Olfactory Bulb Theta Rhythm Follows All Frequencies of Diaphragmatic Respiration in the Freely Behaving Rat

    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Frontiers - Publisher Connector ORIGINAL RESEARCH ARTICLE published: 11 June 2014 BEHAVIORAL NEUROSCIENCE doi: 10.3389/fnbeh.2014.00214 The olfactory bulb theta rhythm follows all frequencies of diaphragmatic respiration in the freely behaving rat Daniel Rojas-Líbano 1,2†, Donald E. Frederick 2,3, José I. Egaña 4 and Leslie M. Kay 1,2,3* 1 Committee on Neurobiology, The University of Chicago, Chicago, IL, USA 2 Institute for Mind and Biology, The University of Chicago, Chicago, IL, USA 3 Department of Psychology, The University of Chicago, Chicago, IL, USA 4 Departamento de Anestesiología y Reanimación, Facultad de Medicina, Universidad de Chile, Santiago, Chile Edited by: Sensory-motor relationships are part of the normal operation of sensory systems. Sensing Donald A. Wilson, New York occurs in the context of active sensor movement, which in turn influences sensory University School of Medicine, USA processing. We address such a process in the rat olfactory system. Through recordings of Reviewed by: the diaphragm electromyogram (EMG), we monitored the motor output of the respiratory Thomas A. Cleland, Cornell University, USA circuit involved in sniffing behavior, simultaneously with the local field potential (LFP) of Emmanuelle Courtiol, New York the olfactory bulb (OB) in rats moving freely in a familiar environment, where they display University Langone Medical Center, a wide range of respiratory frequencies. We show that the OB LFP represents the sniff USA cycle with high reliability at every sniff frequency and can therefore be used to study the *Correspondence: neural representation of motor drive in a sensory cortex.
  • Paroxysmal Bilateral Dysosmia Treated by Resection of the Olfactory Bulbs

    Paroxysmal Bilateral Dysosmia Treated by Resection of the Olfactory Bulbs

    160 Surg Neurol 1993 ;40:160-3 Paroxysmal Bilateral Dysosmia Treated by Resection of the Olfactory Bulbs J.M. Markert, M.D., D.O. Hartshorn, M.D., and S.M. Farhat, M.D. Department of Surgery, Section of Neurosurgery and Department of Otolaryngology, Head and Neck Surgery, University of Michigan Medical Center, and Catherine McAuley Health Center, Ann Arbor, Michigan Markert JM, Hartshorn DO, Farhat SM. Paroxysmal bilateral Case Report dysosmia treated by resection of the olfactory bulbs. Surg Neurol 1993;40:160-3. P.G., a 37-year-old woman, was seen in November 1988. She reported a 17 year history of dysosmia with paroxysms of peculiar sensations of smell. These sensa- Dysosmia, or the distortion of olfaction, is most commonly tions were usually brought on by inhalation of other preceded by viral illness or head trauma, but has a variety strong odors, such as cigars, perfume, or onions; how- of etiologies. The precise nature of the disease process remains obscure. Medical management is largely empiric, ever, they also could be triggered by sudden turning of and has been aimed at treating underlying illnesses, re- the head, a big sniff, or emotional and physical stress. stricting triggering medications, as well as various phar- The common cold or flu would also exacerbate the sensa- macologic interventions. Successful eradication of a severe tion. Dysosmia paroxysms were described as unlike any case of persistent unilateral paroxysmal dysosmia with other odor, and always the same: of a hot, foul and resection of the ipsilateral olfactory bulb has been re- smoky nature on the right, and a sickeningly sweet, ported.
  • Smell & Taste.Pdf

    Smell & Taste.Pdf

    Smell and Taste 428 Special senses 1. SMELL (OLFACTION) 1.1 Overview Smell is the least Understood sense. It is mainly subjective. In dogs and other animals, it is more developed than humans. - There are dfferent stimuli that can be smelled such as: camphoraceous, musky, flora (flower), pepperminty, ethereal, pungent, putrid 1.2 Structure of Olfactory epithelium and bulb See the figure on the next page! 1.2.1 Olfactory mucous membrane It is the upper lining of the nasal cavity (near the septum), containing olfactory (odorant) receptors that are responsible for smelling. o Olfactory receptors are bipolar neurons which receive stimuli in the nasal cavity (through cilia) and transmits them through axons, leave the olfactory epithelium and travel into CNS (olfactory bulb). o Although they are nerve cells, olfactory receptor cells are replaced every 60 days or so, and they grow their axon into the correct place in CNS. Olfactory epithelium contains three types of cells (the olfactory receptors cells discussed) as well as two other types of cells: o Olfactory (Bowman’s) glands: produce mucus that dissolves odorants o Supporting cell o Basal cells: regenerate olfactory receptor cells. 1 Smell and Taste 428 1.2.2 Olfactory bulb The olfactory bulb is made up of nerves that receive olfactory signals from axons of olfactory receptor cells. These nerves are of two cell types: o Mitral cells (most important) (M) o Tufted cells (smaller than mitral cells) (T) Mitral and tufted cells release glutamate The synapse between the axons of olfactory receptor cells and dendrites of mitral cells occur in clusters called olphactory glomeruli (OG) In a glomerulus, about 1000 olfactory receptor axons converge onto 1 mitral cell.