adam quick md department of neurology the ohio state university college of medicine the chemical...
TRANSCRIPT
Adam Quick MD
Department of Neurology
The Ohio State University
College of Medicine
The Chemical Senses – Taste and Olfaction
Objectives
• Describe which sensory systems comprise the chemical senses
• Differentiate between “flavor” and taste• Recognize the pathological states affecting the chemical
senses and the consequences of abnormalities in these systems.
• Describe the basic anatomy of the gustatory and olfactory systems.
• Describe the anatomy and physiology of the gustatory and olfactory systems
At the end of the module, you will learn to:
WHAT ARE THE CHEMICAL SENSES?
Senses that respond to chemicals.
Taste Olfaction Chemesthesis (Common Chemical Sense-often response to noxious
chemical stimuli)
WHERE ARE THE CHEMICAL SENSES?
NASAL CAVITY Olfaction
olfactory nerve Vomeronasal
vomeronasal nerve
Chemesthesis trigeminal
ORAL CAVITY Gustation
facial, glossopharngeal, vagal
Chemesthesis trigeminal
Normal Function
Reward Enjoyment of a
meal Smell of the
ocean Cool feeling of
eucalyptus vapors
Warning Spoiled milk Noxious fumes
like gas or smoke Burning quality of
ammonia
What are chemosensory disorders?
GUSTATION Aguesia Hypoguesia Dysguesia Hyperguesia Gustatory
Agnosia
OLFACTION Anosmia Hyposmia Dysosmia Hyperosmia Olfactory
Agnosia
How important is “TASTE”?
What is the definition of taste?
What happens when we lose “taste”?
“FLAVOR” is a more accurate descriptor of chemosensory perception.
oral cavity “TASTE”gustatio
ntactilethermalpain
nasal cavity “SMELL”olfactioncommon
chemical sense
Consequences of Loss of Flavor
• Indiscriminate Eating• Reduced drive to consume food
because food is “bland”• Results in weight loss and
malnutrition• Compensatory Eating
• Increased use of non-olfactory sensory components
• Often leads to high salt, high sugar diets
CLINICAL ETIOLOGY
Data of complaints from 750 patients
77% complain of TASTE loss
CLINICAL ETIOLOGY
77% complain of some taste loss
3% have some tasteloss
Causes of Olfactory Dysfunction
Nasal/Sinus Disease (NSD) Not completely understood; chronic inflammation and
changes in mucous probably important Nasal polyps
Upper Respiratory Infection (URI) Not completely understood; degeneration of olfactory receptor
neurons noted
Head Trauma- cribiform plate Neurodegenerative disorders Neoplasms (Specific Anosmias- born without specific odorant
receptor)
Possible Causes of Taste Dysfunction
Common Infections Bell’s Palsy Drugs-
including diffusion from blood
Oral Appliances
Dental procedures
Periodontal disease
Salivary disturbance
Less Common Vitamin, trace metal
deficiency CNS Tumor Head Trauma Toxic chemical
exposure Radiation treatment
Uncommon Psychiatric
disorder Epilepsy Migraine Sjogren’s Endocrine
disorder
Olfaction
The nasal cavity• Flavor is mostly
olfaction
• Even in visually oriented species many thousands of different odorants can be detected
• 10,000 in most people
Occupies about 1-2 cm2 of the roof of the nasal cavity
Olfactory receptor neurons are continually replenished throughout life, ½ life of about 60 days
Olfactory epithelium
Olfactory Receptor Neurons
The seven transmembrane olfactory receptors
Only one receptor gene expressed per ORN easily explains prevalence of specific anosmias
Each receptor responds to >1 odorant Human ~ 300s; mouse ~ 1,000 Transduction similar to visual system
ORNs expressing the same receptor project to the same glomeruli
The olfactory bulb
The first processing station of olfactory information
Different odorants activate different collections of glomeruli
Central Olfaction
Ant. Olfactory Nucleus
Pyriform Cortex Olfactory tubercle Amygdala Entorhinal Cortex
• Does not include a thalamus-cortex relay, but has direct projections to limbic system
• Olfactory stimuli can easily evoke emotional responses
soft palate epiglottis cheeks
(rare) lips (rare)
LINGUAL EXTRALINGUAL
Filiform papillae sense tactile, thermal and
chemical stimuli
A quick look at gustationTaste Buds- located on papillae
The Taste Bud
Highly variable in number from person to person (average of about 5000)
Taste ReceptorsSWEET
• T1R• T1R1/T1R2
BITTER
• T2R• 33 members• Mostly co-
expressed
SALTY
• Ion Channel
SOUR
• Ion Channel
UMAMI
• T1R family• T1R2/T1R3
T1R “Sweet” T2R “Bitter
Epithelial Sodium Channel
Cranial Nerves Carrying Taste
1) Facial nerve: chorda tympani and greater superficial petrosal branches from anterior tongue and palate2) Glossopharyngeal nerve: posterior tongue3) Vagus nerve: epiglottis
Gustatory Cortex
Hypothalamus and amygdala
Taste Central Projections
Summary
Chemical senses consist of olfaction, gustation and chemethesis
Taste is a neurological sensation, but flavor is a multimodality integrated sensory experience
People often complain of inability to “taste” subjectively, but most often it is their experience of “flavor” that is diminished. This is frequently related to problems with olfaction.
Many disorders of the upper airways and central nervous system can affect the senses of olfaction and gustation and abnormalities in these sensory modalities can have significant physical consequences.
Chemical Senses Taste and Olfaction Quiz
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