Hair cells

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Transcript Hair cells

10-26
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Receptors are exteroceptors because respond
to chemicals in external environment
Interoceptors respond to chemicals in internal
environment
10-27
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Detects sweet,
sour, salty, bitter,
& amino acids
(umami)
Taste receptor
cells are modified
epithelial cells
◦ 50-100 are in each
taste bud
 Each bud can respond
to all categories of
tastants
Fig 10.7
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Salty & sour do not have receptors; act by passing
through channels
Fig 10.8
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Sweet & bitter have receptors; act thru G-proteins
Fig
10.8
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Olfactory apparatus
consists of receptor
cells, supporting
cells, & basal cells
Fig 10.9
◦ Receptor cells are
bipolar neurons that
send axons to
olfactory bulb
◦ Basal cells are stem
cells that produce
new receptor cells
every 1-2 months
◦ Supporting cells
contain detoxifying
enzymes
10-32
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Odor molecules bind to receptors & act through
G-proteins
Olfactory receptor gene family is huge
10-33
10-34
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Sound waves
funneled by
pinna (auricle)
into external
auditory meatus
External auditory
meatus channels
sound waves to
tympanic
membrane
Fig 10.17
10-47
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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
10-49
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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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Consists of a tube wound 3 turns & tapered so
looks like snail shell
Fig 10.19
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Tube is
divided into 3
fluid-filled
chambers
◦ Scala vestibuli,
cochlear duct,
scala tympani
Fig 10.19
10-52
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Oval window attached to scala vestibuli (at base
of cochlea)
Vibrations at oval window induce pressure waves
in perilymph fluid of scala vestibuli
Scalas vestibuli & tympani are continuous at apex
◦ So waves in vestibuli pass to tympani & displace round
window (at base of cochlea)
 Necessary because fluids are incompressible & waves would not
be possible without round window
10-53
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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
10-54
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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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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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Pressure waves moving thru cochlear duct create
shearing forces between basilar & tectorial
membranes, moving & bending stereocilia
◦ Causing ion channels to open, depolarizing hair cells
◦ The greater the displacement, the greater the amount of
NT released & APs produced
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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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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
10-59
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Conduction deafness occurs when transmission
of sound waves to oval window is impaired
◦ Impacts all frequencies
◦ Helped by hearing aids
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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
10-60
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Provides sense of
equilibrium
◦ =orientation to gravity
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Vestibular apparatus
& cochlea form inner
ear
V. apparatus
consists of otolith
organs (utricle &
saccule) &
semicircular canals
Fig 10.11
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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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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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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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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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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 sensitive
to horizontal
acceleration
Fig 10.14
◦ Hairs pushed
backward during
forward
acceleration
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Saccule
sensitive to
vertical
acceleration
 Hairs pushed
upward when
person descends
10-41
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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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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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Fig 10.16
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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
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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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