Ears & Hearing 10-34.
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Transcript of Ears & Hearing 10-34.
Ears & Hearing 10-34 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 10-47 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 10-49 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 10-50 Ears & Hearing -
Cochlea
Consists of a tube wound 3 turns & tapered so looks like snail
shell Fig 10.19 10-51 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 10-54 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 10-55 Spiral Organ (Organ of Corti)
Fig 10.22 Is where sound is transduced Sensory hair cells located
on the basilar membrane 1 row of inner cells extend length of
basilar membrane Multiple rows of outer hair cells are embedded in
tectorial membrane 10-56 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 10-58
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 10-59 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 10-60 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 10-35 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 10-42 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 10-37 Vestibular Apparatus continued
Hair cells are receptors for equilibrium Each contains hair-like
extensions called stereocilia 1 of these is a kinocilium Fig 10.13
10-38 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 10-39
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 10-40 Utricle & Saccule continued
Fig 10.14 Utricle sensitive to horizontal acceleration Hairs pushed
backward during forward acceleration Saccule sensitive to vertical
acceleration Hairs pushed upward when person descends 10-41
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 10-42 Semicircular Canals continued
Hair cell processes are embedded in cupula of crista ampullaris
When endolymph moves cupula moves Sensory processes bend in
opposite direction of angular acceleration Fig 10.15 10-43 Neural
Pathways for Equilibrium & Balance
Fig 10.16 10-44 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 10-45