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41 - Smell
- from PART IV - DISORDERS OF THE SPECIAL SENSES
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- By Richard L. Doty, Smell and Taste Center, University of Pennsylvania Medical Center, Philadelphia, PA, USA, Steven M. Bromley, Neurological Institute of New York, Columbia-Presbyterian Medical Center, New York, NY, USA
- Edited by Arthur K. Asbury, University of Pennsylvania School of Medicine, Guy M. McKhann, The Johns Hopkins University School of Medicine, W. Ian McDonald, University College London, Peter J. Goadsby, University College London, Justin C. McArthur, The Johns Hopkins University School of Medicine
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- Book:
- Diseases of the Nervous System
- Published online:
- 05 August 2016
- Print publication:
- 11 November 2002, pp 595-609
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- Chapter
- Export citation
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Summary
Possibly owing to the fact that, historically, most disorders of smell function have been difficult to diagnose and treat, physicians often downplay this sense in the routine neurological examination. This is unfortunate when one considers that olfactory disorders are relatively common and profoundly effect a patient's quality of life. Along with its sister sense of taste (see Chapter 42), olfaction determines, among other things, the flavour of foods and beverages, and provides an early warning system for detecting leaking natural gas, spoiled food, fire and other adverse environmental situations. Importantly, olfactory disturbances can be an early sign of such serious diseases or anomalies as Alzheimer's disease, idiopathic Parkinson's disease, epilepsy, multiple sclerosis, and schizophrenia. Although some patients initially present with a frank complaint of a smell disturbance, others are unaware of their dysfunction, pointing out the need for routine quantitative olfactory assessment, which is now easily performed in the office.
In this chapter, we (a) summarize key aspects of olfactory anatomy and physiology, (b) present up-to-date practical techniques for themanagementandquantitative evaluation of the olfactory system, and (c) describe basic olfactory disorders commonly encountered in the neurological setting.
Anatomy and physiology
Olfactory neuroepithelium: a portal to the central nervous system
The olfactory receptors are located within a ∼ 2 cm2 neuroepithelium lining the cribriform plate and regions of the superior turbinate, middle turbinate, and septum. The neurologist should be aware of the fact that, in addition to the main olfactory system (CN I), other specialized neural systems are present in the nose. These include (a) trigeminal (CN V) afferents responsible, for example, for the coolness of menthol vapours (Doty, 1995a), (b) a rudimentary and non-functional vomeronasal organ (VNO) near the base of the septum (Bhatnagar & Meisami, 1998; Smith & Bhatnagar, 2000), and (c) the poorly understood nervus terminalis or terminal nerve (CN O). CN O, a highly conserved neural plexus that ramifies throughout the nasal epithelium, is distinguished by ganglia at nodal points and a high gonadotropin content, and presumably plays no role in human odour perception (Schwanzel-Fukuda & Pfaff, 1995).
42 - Taste
- from PART IV - DISORDERS OF THE SPECIAL SENSES
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- By Steven M. Bromley, Smell & Taste Center, University of Pennsylvania Medical Center, Philadelphia, PA, USA, Richard L. Doty, Smell & Taste Center, University of Pennsylvania Medical Center, Philadelphia, PA, USA
- Edited by Arthur K. Asbury, University of Pennsylvania School of Medicine, Guy M. McKhann, The Johns Hopkins University School of Medicine, W. Ian McDonald, University College London, Peter J. Goadsby, University College London, Justin C. McArthur, The Johns Hopkins University School of Medicine
-
- Book:
- Diseases of the Nervous System
- Published online:
- 05 August 2016
- Print publication:
- 11 November 2002, pp 610-620
-
- Chapter
- Export citation
-
Summary
Taste modifies the act of eating, and subsequently has a tremendous impact on one's behaviour and well-being. The physiologic role of the gustatory system is multifold and includes: (a) triggering ingestive and digestive reflex systems that alter the secretion of oral, gastric, pancreatic, and intestinal juices (Schiffman, 1997; Giduck et al., 1987), (b) reinforcing the ingestive process by enhancing the feelings of pleasure and satiety (Warwick et al., 1993), and (c) enabling the individual to determine the quality of sampled foodstuffs and distinguish nutrients (which usually taste ‘good’) from potential toxins (which usually taste ‘bad’) (McLaughlin & Margolskee, 1994; Scott & Giza, 1995). Although rarely appreciated, gustatory dysfunction can alter food choices and patterns of consumption, resulting in weight loss, malnutrition, and possibly impaired immunity (Schiffman & Wedral, 1996; Mattes & Cowart, 1994). Increased sensitivity and aversion to bitter-tasting substances on the part of the pregnant mother during the first trimester presumably reflects the need to detect and avoid bitter tasting poisons and teratogens during this critical phase of fetal development. Similarly, increased preferences for salty and bitter tasting substances during the remainder of pregnancy likely encourage the eating of a varied diet and the ingestion of much needed electrolytes to expand fluid volume (Duffy et al., 1998). In someone who is hypertensive or diabetic, taste loss can lead to a dangerous tendency to over-compensate for the loss by adding additional salt or sugar to the food.
In this chapter, we review clinically important aspects of the anatomy and physiology of the gustatory system, describe approaches for quantitatively evaluating this system, and present examples of common types of gustatory dysfunction, along with means for their management or treatment.
Anatomy and physiology
Taste buds, papillae, and initiation of taste transduction
The ̴ 4600 goblet-shaped taste buds are located on the tongue's dorsal surface, the tongue–cheek margin, the base of the tongue, the soft palate, the pharynx, the larynx, the epiglottis, the uvula, and the first third of the esophagus (Miller, 1995). Most are found on the surface of the tongue within the protruding papillae. The fungiform, foliate and vallate (also called circumvallate) papillae harbor most of the taste buds; filiform papillae do not (Fig. 42.1).