chapter 17: the special senses muse bio 2440 lecture #4 5/21/13
TRANSCRIPT
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Chapter 17: The Special Senses
Muse Bio 2440Lecture #4 5/21/13
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Comparison of General and Special Senses
General Senses Include somatic
sensations (tactile, thermal, pain, and proprioceptive) and visceral sensations.
Scattered throughout the body.
Simple structures.
Special Senses Include smell, taste,
vision, hearing and equilibrium.
Concentrated in specific locations in the head.
Anatomically distinct structures.
Complex neural pathway.
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Olfaction: Sense of Smell 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.
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Olfactory Epithelium and Olfactory Receptors
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Olfactory Epithelium and Olfactory Receptors continued…
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Smell (Olfaction)
Olfactory Pathways
Arriving information reaches information centers
without first synapsing in thalamus
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Figure 15.21a
Olfactory tract
Olfactory bulb
(a)
Nasalconchae
Route ofinhaled air
Olfactoryepithelium
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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 bulb
Glomeruli
Axon
Olfactory receptor cell
Mucus
Route of inhaled aircontaining odor molecules(b)
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Physiology of Olfaction
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.
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Olfactory transduction
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Figure 17-2 Olfactory and Gustatory Receptors
Olfaction and gustation are specialsenses that provide us with vitalinformation 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.
Stimulus
Dendrites
Specializedolfactoryneuron
to CNS
Stimulusremoved
Actionpotentials
Stimulus
Threshold
Generator potential
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Summary of sense of smellOdorant molecule binds one of 10-100 million receptors.Conformational change in receptor interacts with G proteinG protein activates adenylate cyclase to generate cAMPcAMP opens Na+ channels to initiate depolarization. Information on number of action potentials decoded by olfactorybulbs.
Animals have greater numbers of receptors thus better sense of smellUsually 10,000 times greater.
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Sense of Taste
Receptor organs are taste buds Found on the tongue
On the tops of fungiform papillae On the side walls of foliate papillae and circumvallate
(vallate) papillae
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Figure 15.23b
(b) Enlarged section of a circumvallate papilla.
Taste bud
Circumvallate papilla
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Figure 15.23a
(a) Taste buds are associated with fungiform, foliate, and circumvallate (vallate) papillae.
Fungiform papillae
Epiglottis
Palatine tonsil
Foliate papillae
Lingual tonsil
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Gustation: Sense of Taste
Taste bud
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Structure of a Taste Bud
Flask shaped 50–100 epithelial cells:
Basal cells—dynamic stem cells Gustatory cells—taste cells
Microvilli (gustatory hairs) project through a taste pore to the surface of the epithelium
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Figure 17-3b Gustatory Receptors
Tastebuds
Circumvallate papilla
Fungiform papilla
Filiform papillae
The structure and representative locationsof the three types of lingual papillae. Tastereceptors are located in taste buds, whichform pockets in the epithelium of fungiform or circumvillate papillae.
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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 (Gustation)
Gustatory Discrimination
Primary taste sensations
Sweet (sugars)
Salty
Sour (acids)
Bitter (alkali)
umami - savory (fat)
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Taste Sensations - chemical triggers There are five basic taste sensations
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
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Taste (Gustation)
Gustatory Discrimination Dissolved chemicals contact taste hairs
Bind to receptor proteins of gustatory cell
Salt and sour receptors
Chemically gated ion channels
Stimulation produces depolarization of cell
Sweet, bitter, and umami stimuli
G proteins: (proteins that bind GTP- secondary messengers)
gustducins
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Figure 17-2 Olfactory and Gustatory ReceptorsReceptor cell
Stimulusremoved
Stimulus
Threshold
Receptor depolarization
Stimulus
Receptorcell
Synapse
Axon ofsensoryneuron
Stimulus
Axon
Actionpotentials
Generator potential
Synapticdelay
to CNS
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Figure 17-2 Olfactory and Gustatory Receptors
Salt receptors and sour receptors are chemically gated ion channels whose stimulation produces depolarization of the cell.
Salt and Sour Receptors
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.
Sweet, Bitter, and Umami Receptors
Sour,salt Gated ion
channel
Resting plasmamembrane
Channel opens
Depolarizedmembrane
Sweet,bitter, orumami Membrane
receptor
ActiveG protein
InactiveG protein
ActiveG protein
Inactive2nd messenger
Active2nd messenger
Depolarization of membranestimulates release of chemicalneurotransmitters.
Activation of second messengers stimulates release of chemical neurotransmitters.
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Anatomy of Taste Buds and Papillae Taste bud- made of three types of epithelial
cells: supporting cells, gustatory receptor cells and basal cells.
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
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.
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Influence of Other Sensations on Taste Taste is 80% smell Thermoreceptors, mechanoreceptors,
nociceptors in the mouth also influence tastes Temperature and texture enhance or detract
from taste
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Gustatory Pathway
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Specialist taste buds map to certain regions of tongueMaps differ somewhat , but generally
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Actions of the Major Tastants
15-30