Transcript 5/21/13 Lecture 4 Special senses Smell and Taste

Chapter 17: The Special Senses
Muse Bio 2440
Lecture #4 5/21/13
Comparison of General and Special
Senses
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General Senses
Include somatic
sensations (tactile,
thermal, pain, and
proprioceptive) and
visceral sensations.
Scattered throughout the
body.
Simple structures.
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Special Senses
Include smell, taste,
vision, hearing and
equilibrium.
Concentrated in specific
locations in the head.
Anatomically distinct
structures.
Complex neural pathway.
Olfaction: Sense of Smell
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Olfactory epithelium contains 10-100 million
receptors.
Olfactory receptor- a bipolar neuron with cilia
called olfactory hairs.
- Respond to chemical stimulation of an
odorant molecule.
Supporting cells- provide support and
nourishment.
Basal cells- replace olfactory receptors.
Olfactory Epithelium and Olfactory
Receptors
Olfactory Epithelium and Olfactory
Receptors continued…
Smell (Olfaction)
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Olfactory Pathways
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Arriving information reaches information centers
without first synapsing in thalamus
Olfactory
epithelium
Olfactory tract
Olfactory bulb
Nasal
conchae
(a)
Route of
inhaled air
Figure 15.21a
Olfactory
tract
Mitral cell (output cell)
Glomeruli
Olfactory bulb
Cribriform plate of ethmoid bone
Filaments of olfactory nerve
Lamina propria connective tissue
Olfactory
gland
Axon
Basal cell
Olfactory receptor cell
Olfactory
epithelium
Supporting cell
Dendrite
Olfactory cilia
Mucus
(b)
Route of inhaled air
containing odor molecules
Figure 15.21a
Physiology of Olfaction
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Can detect about 10,000 different odors.
Odorant binds to the receptor of an olfactory
hair→ G-protein activation→ activation of
adenylate cyclase→ production of cAMP→
opening of Na+ channels→ inflow of Na+
→generator potential→ nerve impulse
through olfactory nerves→ olfactory bulbs→
olfactory tract→ primary olfactory area of the
cerebral cortex.
Olfactory transduction
Figure 17-2 Olfactory and Gustatory Receptors
Olfaction and gustation are special
senses that provide us with vital
information about our
environment. Although the sensory
information provided is diverse
and complex, each special sense
originates at receptor cells that
may be neurons or specialized
receptor cells that communicate
with sensory neurons.
Action
potentials
Stimulus
Dendrites
Specialized
olfactory
neuron
Stimulus
removed
Stimulus
Threshold
Generator potential
to CNS
Summary of sense of smell
Odorant molecule binds one of 10-100 million receptors.
Conformational change in receptor interacts with G protein
G protein activates adenylate cyclase to generate cAMP
cAMP opens Na+ channels to initiate depolarization.
Information on number of action potentials decoded by olfactory
bulbs.
Animals have greater numbers of receptors thus better sense of smell
Usually 10,000 times greater.
Sense of Taste
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Receptor organs are taste buds
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Found on the tongue
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On the tops of fungiform papillae
On the side walls of foliate papillae and circumvallate
(vallate) papillae
Circumvallate papilla
Taste bud
(b) Enlarged section of a
circumvallate papilla.
Figure 15.23b
Epiglottis
Palatine tonsil
Lingual tonsil
Foliate papillae
Fungiform papillae
(a) Taste buds are associated with fungiform,
foliate, and circumvallate (vallate) papillae.
Figure 15.23a
Gustation: Sense of Taste
Taste bud
Structure of a Taste Bud
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Flask shaped
50–100 epithelial cells:
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Basal cells—dynamic stem cells
Gustatory cells—taste cells
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Microvilli (gustatory hairs) project through a taste pore to
the surface of the epithelium
Figure 17-3b Gustatory Receptors
Taste
buds
Circumvallate papilla
Fungiform papilla
Filiform papillae
The structure and representative locations
of the three types of lingual papillae. Taste
receptors are located in taste buds, which
form pockets in the epithelium of
fungiform or circumvillate papillae.
Connective
tissue
Gustatory
hair
Taste fibers
of cranial
nerve
Basal
cells
Gustatory
(taste) cells
Taste
pore
Stratified
squamous
epithelium
of tongue
(c) Enlarged view of a taste bud.
Figure 15.23c
Taste (Gustation)
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Gustatory Discrimination
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Primary taste sensations
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Sweet (sugars)
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Salty
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Sour (acids)
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Bitter (alkali)
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umami - savory (fat)
Taste Sensations - chemical triggers
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There are five basic taste sensations
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Sweet—sugars, saccharin, alcohol, and some
amino acids
Sour—hydrogen ions
Salt—metal ions
Bitter—alkaloids such as quinine and nicotine
Umami—amino acids glutamate and aspartate
Taste (Gustation)
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Gustatory Discrimination
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Dissolved chemicals contact taste hairs
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Bind to receptor proteins of gustatory cell
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Salt and sour receptors
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Chemically gated ion channels
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Stimulation produces depolarization of cell
Sweet, bitter, and umami stimuli
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G proteins: (proteins that bind GTP- secondary messengers)
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gustducins
Figure 17-2 Olfactory and Gustatory Receptors
Receptor cell
Stimulus
Stimulus
removed
Stimulus
Receptor
cell
Threshold
Receptor depolarization
Synapse
Axon of
sensory
neuron
Axon
Stimulus
Action
potentials
Synaptic
delay
to CNS
Generator potential
Figure 17-2 Olfactory and Gustatory Receptors
Salt and Sour Receptors
Sweet, Bitter, and Umami Receptors
Salt receptors and sour receptors are
chemically gated ion channels whose
stimulation produces depolarization
of the cell.
Receptors responding to stimuli that produce
sweet, bitter, and umami sensations are
linked to G proteins called gustducins
(GUST-doos- inz)protein complexes that
use second messengers to produce their
effects.
Sour,
salt
Gated ion
channel
Sweet,
bitter, or
umami
Membrane
receptor
Resting plasma
membrane
Inactive
G protein
Active
G protein
Channel opens
Depolarized
membrane
Active
G protein
Active
2nd messenger
Depolarization of membrane
stimulates release of chemical
neurotransmitters.
Inactive
2nd messenger
Activation of second messengers stimulates
release of chemical neurotransmitters.
Anatomy of Taste Buds and Papillae
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Taste bud- made of three types of epithelial
cells: supporting cells, gustatory receptor
cells and basal cells.
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About 50 gustatory cells per taste bud. Each
one has a gustatory hair that projects through
the taste pore.
Taste buds are found in the papillae.
Three types of papillae: vallate
(circumvallate), fungiform and foliate.
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Physiology of Gustation
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Five types of taste: sour, sweet, bitter,
salty and umami.
Tastant dissolves in saliva → plasma
membrane of gustatory hair→ receptor
potential→ nerve impulse via cranial
nerves VII, IX and X→ medulla→
thalamus→ primary gustatory area of the
cerebral cortex.
Influence of Other Sensations on
Taste
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Taste is 80% smell
Thermoreceptors, mechanoreceptors,
nociceptors in the mouth also influence tastes
Temperature and texture enhance or detract
from taste
Gustatory Pathway
Specialist taste buds map to certain
regions of tongue
Maps differ somewhat , but generally
Actions of the Major Tastants
15-30