smell, taste, and hearing

1. section 2, chapter 12
Smell, Taste, and Hearing
• Sensory receptors are within large, complex sensory
organs in the head
• Smell in olfactory organs
• Taste in taste buds
• Hearing and equilibrium in ears
• Sight in eyes
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2. Sense of Smell
• Olfactory receptors
• Bipolar Chemoreceptors
• Respond to chemicals (called odorants) dissolved in liquids
• Olfactory organs
• Olfactory epithelium - contain olfactory receptors and
supporting epithelial cells
• Cover parts of nasal cavity, superior nasal conchae, and a
portion of the nasal septum
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3. Olfactory Receptors
Figure 12.5 Olfactory receptors. (a) columnar epithelial cells support olfactory
receptor cells, which have cilia at their distal ends. The olfactory receptors pass
through olfactory foramina in the cribriform plate and synapse with the olfactory
bulb in the brain.
(b) Olfactory epithelium cover the upper nasal cavity and superior nasal conchae.

4. Olfactory Nerve Pathways
• Once olfactory receptors are stimulated, nerve impulses travel through
•
•Olfactory nerves
olfactory bulbs
olfactory tracts
limbic system (for emotions) & olfactory cortex (for interpretation)
The limbic system, which is involved with emotions and
memory is strongly effected by smell.
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5. Olfactory Stimulation
• Olfactory organs located high in the nasal cavity above the
usual pathway of inhaled air
• Olfactory receptors undergo sensory adaptation rapidly
• Sense of smell drops by 50% within a second after
stimulation
• Olfactory code
• Hypothesis
• Odor that is stimulated by a distinct set of receptor cells and
its associated receptor proteins
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6. Sense of Taste
• Taste buds
• Organs of taste
• Located on papillae of tongue, roof of mouth, linings of
cheeks and walls of pharynx
• Taste receptors
• Chemoreceptors
• Taste cells – modified epithelial cells that function as
receptors
• Taste hairs –microvilli that protrude from taste cells;
sensitive parts of taste cells
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7. Taste Receptors
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Papillae
Taste buds
Epithelium
of tongue
(a)
Taste cell
Taste hair
Supporting
cell
Taste
pore
Connective
tissue
Sensory
nerve fibers
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(b)

8. Taste Sensations
• Four primary taste sensations
• Sweet – stimulated by carbohydrates
• Sour – stimulated by acids
• Salty – stimulated by salts
• Bitter – stimulated by many organic compounds
• Spicy foods activate pain receptors
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9. Taste Nerve Pathways
• Sensory impulses from taste receptors travel along:
• Cranial nerves to…
• Medulla oblongata to…
• Thalamus to…
• Gustatory cortex (for interpretation)
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10. Sense of Hearing
• Ear
• Organ of hearing
• Three (3) sections:
• External ear
• Middle ear
• Inner ear
10

11. External Ear
• Auricle
• Collects sounds waves
• External auditory meatus
• Lined with ceruminous
glands
• Carries sound to
tympanic membrane
• Terminates with
tympanic membrane
• Tympanic membrane
• Vibrates in response to
sound waves
Auricle
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Semicircular
canals
Incus
Stapes
Malleus
Cochlea
Vestibulocochlear
nerve
Oval window (under stapes)
Round window
Tympanic cavity
Tympanic
membrane
External acoustic
meatus
Auditory tube
Pharynx
11

12. Middle Ear
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• Tympanic cavity
• Air-filled space in
temporal bone
• Auditory ossicles
• Vibrate in response to
tympanic membrane
• Malleus, incus and stapes
• Hammer, anvil and stirrup
• Oval window
• Opening in wall of
tympanic cavity
• Stapes vibrates against it to
move fluids in inner ear
Auricle
Semicircular
canals
Incus
Stapes
Malleus
Cochlea
Vestibulocochlear
nerve
Oval window (under stapes)
Round window
Tympanic cavity
Tympanic
membrane
External acoustic
meatus
Auditory tube
Pharynx
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13. Auditory Tube
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• Also known as the
Eustachian tube
• Connects middle ear to
throat
• Helps maintain equal
pressure on both sides of
tympanic membrane
• Usually closed by valvelike flaps in throat
Auricle
Semicircular
canals
Incus
Stapes
Malleus
Cochlea
Vestibulocochlear
nerve
Oval window (under stapes)
Round window
Tympanic cavity
Tympanic
membrane
External acoustic
meatus
Auditory tube
Pharynx
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14. Inner Ear
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• Complex system of labyrinths
• Osseous labyrinth
• Bony canal in temporal
bone
• Filled with perilymph
• Membranous labyrinth
• Tube within osseous
labyrinth
• Filled with endolymph
Bony labyrinth
Perilymph
Membranous
labyrinth
Endolymph
Bony labyrinth
(contains perilymph)
Membranous labyrinth
(contains endolymph)
Semicircular
canals
Utricle
Saccule
Vestibular nerve
Cochlear nerve
Scala
vestibuli (cut)
Scala
tympani (cut)
Cochlear
duct (cut)
containing
endolymph
Ampullae Oval Vestibule Round Maculae
window
window
(a)
Cochlea
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15. Inner Ear
• Three (3) parts of labyrinths:
• Cochlea
• Functions in hearing
• Semicircular canals
• Functions in
equilibrium
• Vestibule
• Functions in
equilibrium
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Bony labyrinth
Perilymph
Membranous
labyrinth
Endolymph
Bony labyrinth
(contains perilymph)
Membranous labyrinth
(contains endolymph)
Semicircular
canals
Utricle
Saccule
Vestibular nerve
Cochlear nerve
Scala
vestibuli (cut)
Scala
tympani (cut)
Cochlear
duct (cut)
containing
endolymph
Ampullae Oval Vestibule Round Maculae
window
window
(a)
Cochlea
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16. Cochlea
• Scala vestibuli
• Upper compartment
• Leads from oval
window to apex of
spiral
• Part of bony labyrinth
• Scala tympani
• Lower compartment
• Extends from apex of
the cochlea to round
window
• Part of bony labyrinth
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Stapes vibrating in
oval window
Helicotrema
Scala vestibuli
filled with perilymph
Vestibular
membrane
Basilar
membrane
Scala tympani
filled with
perilymph
Round window
Membranous
labyrinth
Cochlear duct
filled with endolymph
16

17. Cochlea
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• Cochlear duct
• Portion of
membranous labyrinth
in cochlea
• Vestibular membrane
• Separates cochlear
duct from scala
vestibuli
• Basilar membrane
• Separates cochlear
duct from scala
tympani
Scala vestibuli
(contains perilymph)
Vestibular membrane
Branch of
cochlear
nerve
Cochlear duct
(contains endolymph)
Spiral organ (organ of Corti)
Basilar membrane
Scala tympani
(contains perilymph)
(a)
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18. Organ of Corti
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• Group of hearing receptor
cells (hair cells)
• On upper surface of basilar
membrane
• Different frequencies of
vibration move different parts
of basilar membrane
• Particular sound frequencies
cause hairs of receptor cells to
bend
• Nerve impulse generated
Scala vestibuli
(contains perilymph)
Vestibular membrane
Cochlear duct
(contains endolymph)
Spiral organ (organ of Corti)
Branch of
cochlear
nerve
Basilar membrane
Scala tympani
(contains perilymph)
(a)
Tectorial
membrane
Hair cells
(b)
Branch of
cochlear nerve
Nerve
fibers
Supporting
cells
Basilar
membrane
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19. Organ of Corti
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Cochlear duct
Tectorial membrane
Scala tympani
Hair cells
Basilar
membrane
(a)
(b)
a: © John D. Cunningham/Visuals Unlimited; b: © Fred Hossler/Visuals Unlimited
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20. Auditory Nerve Pathways
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Auditory cortex
(temporal lobe)
Thalamus
Medial geniculate
body of thalamus
Midbrain
Pons
Cochlear
nuclei
Superior
olivary
nucleus
Medulla
oblongata
Vestibulocochlear
nerve
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21. Summary of the Generation of
Sensory Impulses from the Ear
21

22. Sense of Equilibrium
• Static equilibrium
• Vestibule
• Senses position of
head when body is not
moving
• Dynamic Equilibrium
• Semicircular canals
• Senses rotation and
movement of head and
body
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23. Vestibule
• Utricle
• Communicates with
saccule and membranous
portion of semicircular
canals
• Saccule
• Communicates with
cochlear duct
• Macula
• Hair cells of utricle and
saccule
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Ampullae of
semicircular
canals
Vestibulocochlear
nerve
Cochlea
Utricle
Cochlear
duct
Maculae Saccule Vestibule
23

24. Macula
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• Responds to changes
in head position
• Bending of hairs
results in generation of
nerve impulse
Hairs of
hair cells bend
Gelatinous
material sags
Otoliths
Macula
of utricle
Hair cells
Sensory nerve fiber
Gravitational
force
Supporting cells
(a) Head upright
(b) Head bent forward
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25. Semicircular Canals
• Three (3) canals at right angles
• Ampulla
• Swelling of membranous
labyrinth that communicates
with the vestibule
• Crista ampullaris
• Sensory organ of ampulla
• Hair cells and supporting
cells
• Rapid turns of head or body
stimulate hair cells
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Ampullae of
semicircular
canals
Vestibulocochlear
nerve
Utricle
Cochlea
Cochlear
duct
Maculae Saccule Vestibule
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26. Crista Ampullaris
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Endolymph
Semicircular canal
Cupula
Crista
ampullaris
(a) Head in still position
Ampulla
Crista ampullaris
Hairs
Hair cell
Supporting cells
Sensory nerve fibers
(b) Head rotating
(c)
End of section 2, chapter 12
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