Transcript Chemical Senses

Ears & Hearing
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Ears & Hearing - Outer Ear
• Sound waves
funneled by pinna
(auricle) into
external auditory
meatus
• External auditory
meatus channels
sound waves to
tympanic
membrane
Fig 10.17
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Ears & Hearing - Middle Ear continued
• Malleus (hammer) is attached to tympanic membrane
– Carries vibrations to incus (anvil)
– Stapes (stirrup) receives vibrations from incus, transmits to
oval window
Fig 10.18
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Ears & Hearing - Middle Ear continued
• Stapedius muscle, attached to stapes, provides
protection from loud noises
– Can contract & dampen large vibrations
– Prevents nerve damage in cochlea
Fig 10.18
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Ears & Hearing - Cochlea
• Consists of a tube wound 3 turns & tapered so
looks like snail shell
Fig 10.19
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Ears & Hearing - Cochlea continued
• Low frequencies can travel all way thru vestibuli & back in
tympani
• As frequencies increase they travel less before passing directly
thru vestibular & basilar membranes to tympani
Fig 10.20
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Ears & Hearing - Cochlea continued
• High frequencies
produce
maximum
stimulation of
Spiral Organ
closer to base of
cochlea & lower
frequencies
stimulate closer
to apex
Fig 10.20
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Spiral Organ (Organ of Corti)
• Is where sound is
transduced
• Sensory hair cells
located on the
basilar membrane
Fig 10.22
– 1 row of inner cells
extend length of
basilar membrane
– Multiple rows of outer
hair cells are
embedded in
tectorial membrane
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Neural Pathway for Hearing
• Info from 8th nerve goes to medulla, then to inferior colliculus,
then to thalamus, & on to auditory cortex
Fig 10.23
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Neural Pathways for Hearing
• Neurons in
different regions of
cochlea stimulate
neurons in
corresponding
areas of auditory
cortex
– Each area of
cortex represents
different part of
cochlea & thus a
different pitch
Fig 10.24
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Hearing Impairments
• Conduction deafness occurs when transmission of
sound waves to oval window is impaired
– Impacts all frequencies
– Helped by hearing aids
• Sensorineural (perceptive) deafness is impaired
transmission of nerve impulses
– Often impacts some pitches more than others
– Helped by cochlear implants
• Which stimulate fibers of 8th in response to sounds
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Vestibular Apparatus
• Provides sense of
equilibrium
– =orientation to gravity
• Vestibular apparatus &
cochlea form inner ear
• V. apparatus consists
of otolith organs
(utricle & saccule) &
semicircular canals
Fig 10.11
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Semicircular Canals
• Provide information
about rotational
acceleration
• Project in 3
different planes
• Each contains a
semicircular duct
• At base is crista
ampullaris where
sensory hair cells
are located
Fig 10.12
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Vestibular Apparatus continued
• Utricle and saccule provide info about linear acceleration
• Semicircular canals, oriented in 3 planes, give sense of angular
acceleration
Fig 10.12
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Vestibular Apparatus continued
• Hair cells are receptors for equilibrium
– Each contains 20-50 hair-like extensions called stereocilia
• 1 of these is a kinocilium
Fig 10.13
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Vestibular Apparatus continued
• When stereocilia are bent toward kinocilium, hair cell
depolarizes & releases NT that stimulates 8th nerve
• When bent away from kinocilium, hair cell hyperpolarizes
– In this way, frequency of APs in hair cells carries information about
movement
Fig 10.13
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Utricle & Saccule
• Have a macula containing hair cells
– Hair cells embedded in gelatinous otolithic membrane
• Which contains calcium carbonate crystals (=otoliths) that resist
change in movement
Fig 10.14
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Utricle & Saccule continued
• Utricle sensitive to
horizontal
acceleration
Fig 10.14
– Hairs pushed
backward during
forward
acceleration
• Saccule sensitive
to vertical
acceleration
• Hairs pushed
upward when
person descends
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Semicircular Canals
• Provide information
about rotational
acceleration
• Project in 3
different planes
• Each contains a
semicircular duct
• At base is crista
ampullaris where
sensory hair cells
are located
Fig 10.12
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Semicircular Canals continued
• Hair cell processes
are embedded in
cupula of crista
ampullaris
• When endolymph
moves cupula
moves
Fig 10.15
– Sensory processes
bend in opposite
direction of angular
acceleration
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Neural Pathways for Equilibrium &
Balance
Fig 10.16
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Nystagmus & Vertigo
• Vestibular nystagmus is involuntary oscillations
of eyes that occurs when spinning person stops
– Eyes continue to move in direction opposite to spin,
then jerk rapidly back to midline
• Vertigo is loss of equilibrium
– Natural response of vestibular apparatus
– Pathologically, may be caused by anything that
alters firing rate of 8th nerve
• Often caused by viral infection
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