copyright © 2010 pearson education, inc. chemical senses chemoreceptors for chemicals in aqueous...
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Copyright © 2010 Pearson Education, Inc.
Chemical Senses
• Chemoreceptors for chemicals in aqueous solution
Copyright © 2010 Pearson Education, Inc.
Sense of Smell
• Olfactory epithelium in roof of nasal cavity
• Olfactory receptor cells with radiating y cilia
• Axons of olfactory receptor cells form olfactory nerve
Copyright © 2010 Pearson Education, Inc. Figure 15.21a
Olfactory tract
Olfactory bulb
(a)
Nasalconchae
Route ofinhaled air
Olfactoryepithelium
Copyright © 2010 Pearson Education, Inc. Figure 15.21a
Mitral cell (output cell)
Olfactorygland
Olfactorytract
Olfactoryepithelium
Filaments of olfactory nerve
Cribriform plate of ethmoid bone
Lamina propria connective tissue
Basal cell
Supporting cell
Dendrite
Olfactory cilia
Olfactory bulbGlomeruli
Axon
Olfactory receptor cell
Mucus
Route of inhaled aircontaining odor molecules(b)
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Physiology of Smell
• Dissolved odorants bind to receptor in cilium membranes
• causing depolarization of receptor membrane that triggers an AP
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Olfactory Pathway
• Receptor synapse with mitral cells - amplify and relay signals along olfactory tracts to the:
• Olfactory cortex
• Hypothalamus and limbic system
Copyright © 2010 Pearson Education, Inc. Figure 15.22
1
2
Odorant bindsto its receptor.
Receptoractivates G protein (Golf).
3 G proteinactivates adenylate cyclase.
4 Adenylatecyclase converts ATP to cAMP.
5 cAMP opens a cation channel allowing Na+ and Ca2+ influx and causing depolarization.
Odorant
G protein (Golf)
Receptor
Adenylate cyclase
OpencAMP-gated
cation channelGDP
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Sense of Taste
• Taste buds on tongue
• Top of fungiform papillae
• Side of foliate papillae and circumvallate (vallate) papillae
Copyright © 2010 Pearson Education, Inc. Figure 15.23a
(a) Taste buds are associated with fungiform, foliate, and circumvallate (vallate) papillae.
Fungiform papillae
Epiglottis
Palatine tonsil
Foliate papillae
Lingual tonsil
Copyright © 2010 Pearson Education, Inc. Figure 15.23b
(b) Enlarged section of a circumvallate papilla.
Taste bud
Circumvallate papilla
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Structure of a Taste Bud
• 50–100 epithelial cells:
• Basal cells—dynamic stem cells
• Gustatory cells—taste cells
• Microvilli (gustatory hairs) project through a taste pore
Copyright © 2010 Pearson Education, Inc. Figure 15.23c
Taste fibersof cranialnerve
Connectivetissue
Gustatory(taste) cells
Tastepore
Gustatoryhair
Stratifiedsquamousepitheliumof tongue
(c) Enlarged view of a taste bud.
Basalcells
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Taste Sensations
• Five basic taste sensations
1.Sweet—sugars, saccharin, alcohol, and some amino acids
2.Sour—hydrogen ions
3.Salt—metal ions
4.Bitter—alkaloids such as quinine and nicotine
5.Umami—amino acids glutamate and aspartate
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Physiology of Taste
• To be tasted, a chemical:
• Must dissolve in saliva
• Contact gustatory hairs
• Depolarizes membrane, causing release of NT
• Initiates a generator potential that elicits an action potential
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Taste Transduction
• The stimulus energy of taste causes gustatory cell depolarization by:
• Na+ influx in salty tastes (directly causes depolarization)
• H+ in sour tastes (by opening cation channels)
• G protein gustducin in sweet, bitter, and umami tastes (leads to release of Ca2+ from intracellular stores, which causes opening of cation channels in the plasma membrane)
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Gustatory Pathway
• Cranial nerves VII and IX carry impulses from taste buds to the solitary nucleus of the medulla
• Impulses then travel to the thalamus and from there fibers branch to the:
• Gustatory cortex in the insula
• Hypothalamus and limbic system (appreciation of taste)
Copyright © 2010 Pearson Education, Inc. Figure 15.24
Gustatory cortex(in insula)
Thalamic nucleus(ventral posteromedialnucleus)
PonsSolitary nucleus inmedulla oblongata
Facial nerve (VII)
Glossopharyngealnerve (IX)
Vagus nerve (X)
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Influence of Other Sensations on Taste
• Taste is 80% smell
• Thermoreceptors, mechanoreceptors, nociceptors in mouth influence taste