Copyright © 2010 Pearson Education, Inc. Chemical Senses Chemoreceptors for chemicals in aqueous solution.

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)

Copyright © 2010 Pearson Education, Inc.

Physiology of Smell

• Dissolved odorants bind to receptor in cilium membranes

• causing depolarization of receptor membrane that triggers an AP

Copyright © 2010 Pearson Education, Inc.

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

Copyright © 2010 Pearson Education, Inc.

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

Copyright © 2010 Pearson Education, Inc.

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

Copyright © 2010 Pearson Education, Inc.

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

Copyright © 2010 Pearson Education, Inc.

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

Copyright © 2010 Pearson Education, Inc.

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)

Copyright © 2010 Pearson Education, Inc.

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)

Copyright © 2010 Pearson Education, Inc.

Influence of Other Sensations on Taste

• Taste is 80% smell

• Thermoreceptors, mechanoreceptors, nociceptors in mouth influence taste