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PowerPoint® Lecture Slides
prepared by
Janice Meeking,
Mount Royal College
CHAPTER
15
The Special
Senses:
Part A
Copyright © 2010 Pearson Education, Inc.
The Eye and Vision
• 70% of all sensory receptors are in the eye
• Nearly half of the cerebral cortex is involved in
processing visual information!
• Most of the eye is protected by a cushion of
fat and the bony orbit
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Eyebrow
Eyelid
Eyelashes
Site where
conjunctiva
merges with
cornea
Palpebral
fissure
Lateral
commissure
Iris
Eyelid
Sclera
Lacrimal
(covered by caruncle
conjunctiva)
(a) Surface anatomy of the right eye
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Pupil
Medial
commissure
Figure 15.1a
Eyebrows
• Overlie the supraorbital margins
• Function in
• Shading the eye
• Preventing perspiration from reaching the eye
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Eyelids
• Protect the eye anteriorly
• Palpebral fissure—slit separating eyelids
• Medial & Lateral Canthi – eye angles
• Caruncle—fleshy elevation at medial canthus;
contains oil and sweat glands
• Tarsal plates—internal supporting C.T. sheet
• Levator palpebrae superioris—gives the upper
eyelid mobility
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Site where
conjunctiva
merges with
cornea
Palpebral
fissure
Lateral
commissure
Eyelid
Sclera
Lacrimal
(covered by caruncle
conjunctiva)
(a) Surface anatomy of the right eye
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Pupil
Medial
commissure
Figure 15.1a
Eyelids
• Eyelashes
• Nerve endings of follicles initiate reflex blinking
• Lubricating glands associated with the eyelids
• Tarsal glands-sebaceous glands that produce
oily secretion to lubricate the eye
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Conjunctiva
• Mucous membranes of the eye
• Palpebral conjunctiva: lines the eyelids
• Bulbar conjunctiva: covers the white of the eyes
(anteriorly)
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Levator palpebrae
superioris muscle
Orbicularis oculi muscle
Tarsal plate
Palpebral conjunctiva
Tarsal glands
Cornea
Palpebral fissure
Bulbar conjunctiva
Orbicularis oculi muscle
(b) Lateral view; some structures shown in sagittal section
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Lacrimal Apparatus
• Consists of: Lacrimal gland and ducts that connect to
nasal cavity
• Releases: dilute salt solution (tears)
• The solution also contains:mucus, antibodies, and
lysozyme (bacteria destroying enzyme)
• Blinking spreads the tears towards the medial canthus,
then into lacrimal puncta to lacrimal canaliculi then
drain into nasolacrimal duct
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Lacrimal sac
Lacrimal gland
Lacrimal punctum
Lacrimal canaliculus
Nasolacrimal duct
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Figure 15.2
Extrinsic Eye Muscles
• The movement of the eye is controlled by six muscles on
the external surface of each eye:
• Superior rectus: elevates eye
• Inferior rectus: depresses eye
• Lateral rectus: moves eye laterally
• Medial rectus: moves eye medially
• Inferior oblique: moves eye up and out
• Superior oblique: moves eye down and out
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Superior oblique
muscle
Superior oblique
tendon
Superior rectus
muscle
Lateral rectus
muscle
Inferior rectus
Inferior oblique
muscle
muscle
(a) Lateral view of the right eye
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Figure 15.3a
Trochlea
Superior oblique
muscle
Superior oblique
tendon
Superior rectus
muscle
Axis at center
of eye
Inferior
rectus muscle
Medial
rectus muscle
Lateral
rectus muscle
Common
tendinous ring
(b) Superior view of the right eye
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Figure 15.3b
Extrinsic Eye Muscles
• The innervations to each muscle can be
remembered by the following equation:
(LR6SO4)O3
• Which means:
• Lateral rectus: controlled by CN # 6
(Abducens)
• Superior oblique: controlled by CN # 4
(Trochelar)
• All others: controlled by CN # 3
(oculomotor)
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Structure of the Eyeball
• The eyeball is composed of three layers
• Fibrous layer
• Vascular layer
• Sensory layer
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Anterior
segment (contains
aqueous humor)
Lens
Posterior segment
(contains vitreous humor)
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Fibrous Layer
• Outermost layer of dense avascular CT
• Two regions: sclera and cornea
1. Sclera:
• Opaque posterior region
2. Cornea:
• Transparent anterior part
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Vascular Layer
• Middle layer
• Three regions: choroid, ciliary body, and iris
1. Choroid region
• Posterior portion
• Supplies blood to most of eyeball
• Brown pigment absorbs light to prevent its
scattering
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Vascular Layer
2.Ciliary body
• Ring of smooth muscle attached to and
surrounding the lens
• Ciliary zonule (suspensory ligament): holds
lens in position
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Vascular Layer
3. Iris (smooth muscle)
• The anterior colored part of the eye
• Pupil: central opening of iris; the iris regulates the
amount of light entering the eye
• Close vision and bright light- pupils constrict
• Distant and dim light- pupils dilate
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Pupillary Sphincter
muscle contraction
decreases pupil size.
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Iris (two muscles)
• Sphincter pupillae
• Dilator pupillae
Dilator
muscle contraction
increases pupil size.
Ciliary body
Ciliary zonule
(suspensory
ligament)
Sclera
Choroid
Iris
Pupil
Optic nerve
Lens
Optic disc
(blind spot)
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Figure 15.4a
Sensory Layer (The Retina)
• Delicate two-layered membrane
• Pigmented layer -Outer layer that absorbs
light and prevents its scattering
• Neural layer – contains photoreceptor cells
(rods and cones), bipolar cells (connect
photoreceptors to ganglion cells), and
ganglion cells (axons form optic nerve)
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Pathway of light
Neural layer of retina
Pigmented
layer of
retina
Choroid
Sclera
Optic disc
Central artery
and vein of retina
Optic
nerve
(a) Posterior aspect of the eyeball
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Figure 15.6a
Ganglion
cells
Bipolar
cells
Photoreceptors
• Rod
• Cone
Amacrine cell
Horizontal cell
Pathway of signal output
Pigmented
layer of retina
Pathway of light
(b) Cells of the neural layer of the retina
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Figure 15.6b
Photoreceptors
• Rods
• More numerous at peripheral region of retina,
away from the fovea centralis (area of retina
containing only cones)
• Operate in dim light
• Provide indistinct, fuzzy, non color peripheral
vision
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Photoreceptors
• Cones
• Densest in center of retina and concentrated
in an area called the fovea centralis (next to
blind spot)
• Operate in bright light
• Provide high-acuity color vision
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Photoreceptors
• Photoreceptor cells are distributed over entire
retina except where the optic nerve leaves the
eye called the blind spot
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Cones
• There are three types of cones named for the
colors of light absorbed: blue, green, and red
• Intermediate hues are perceived by activation
of more than one type of cone at the same
time
• Color blindness is due to a congenital lack of
one or more of the cone types
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Central
artery
and vein
emerging
from the
optic disc
Macula
lutea
Optic disc
Retina
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Figure 15.7
Internal Chambers and Fluids
• The lens and ciliary zonule separate the
anterior and posterior segments
• Posterior segment contains vitreous humor
that:
• Is a clear gel like substance which helps
reinforce the eye internally
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Ciliary body
Ciliary zonule
(suspensory
ligament)
Pupil
Sclera
Choroid
Retina
Macula lutea
Fovea centralis
Posterior pole
Optic nerve
Anterior
segment (contains
aqueous humor)
Lens
Posterior segment
(contains vitreous humor)
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Optic disc
(blind spot)
Figure 15.4a
Internal Chambers and Fluids
• Anterior segment is composed of two
chambers
• Anterior chamber—between cornea and
iris
• Posterior chamber—between iris and
lens
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Internal Chambers and Fluids
• Anterior segment contains aqueous humor
• Watery fluid continuously produced and
drained
• Glaucoma: compression of the retina and optic
nerve if drainage of aqueous humor is blocked
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Iris
Lens
Cornea
Aqueous humor
Anterior Anterior
segment chamber
(contains Posterior
chamber
aqueous
3
humor)
Scleral venous
sinus
Cornealscleral junction
Posterior
segment
(contains
vitreous
humor)
2
Ciliary zonule
(suspensory
ligament)
1
Ciliary body
Ciliary
processes
Ciliary
muscle
Cornea
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Lens
Figure 15.8
Lens
• Biconvex, transparent, flexible,and avascular
• Allows precise focusing of light on the retina
• Cataracts (clouding of lens) occur as a consequence
of aging, diabetes mellitus, heavy smoking, and
frequent exposure to intense sunlight
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Figure 15.9
Ora serrata
Ciliary body
Ciliary zonule
(suspensory
ligament)
Cornea
Iris
Pupil
Anterior pole
Anterior
segment (contains
aqueous humor)
Lens
Scleral venous
sinus
Posterior segment
(contains vitreous humor)
(a) Diagrammatic view. The vitreous
humor is illustrated only in the
bottom part of the eyeball.
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Sclera
Choroid
Retina
Macula lutea
Fovea centralis
Posterior pole
Optic nerve
Central artery
and vein of
the retina
Optic disc
(blind spot)
Figure 15.4a
Refraction and Lenses
• Refraction
• Bending of a light ray when light passes from
one transparent medium to another
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Refraction and Lenses
• Light passing through a convex lens is bent so
that the rays converge at a focal point
• The image formed at the focal point is upsidedown and reversed right to left
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Point sources
Focal points
(a) Focusing of two points of light.
(b) The image is inverted—upside down and reversed.
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Figure 15.12
Focusing Light on the Retina
• Pathway of light entering the eye: cornea, aqueous
humor, lens, vitreous humor, neural layer of retina,
photoreceptors
• Light is refracted
• At the cornea
• Entering the lens
• Leaving the lens
• Change in lens curvature allows for fine focusing of
an image
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Focusing for Distant Vision
• Light rays from distant objects are parallel and
need little refraction
• Ciliary muscles are relaxed
• Lens is stretched flat by tension in the ciliary
zonule
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Sympathetic activation
Nearly parallel rays
from distant object
Lens
Ciliary zonule
Ciliary muscle
Inverted
image
(a) Lens is flattened for distant vision.
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Figure 15.13a
Focusing for Close Vision
• Light from a close object diverges as it
approaches the eye; requires that the eye
make three active adjustments
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Focusing for Close Vision
• Close vision requires
• Accommodation—changing the lens shape by
ciliary muscles to increase refractory power
• Presbyopia—loss of accommodation over age 50
• Constriction—constriction of pupils to prevent the
most divergent rays from entering eye
• Convergence—medial rotation of the eyeballs
toward the object being viewed
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Parasympathetic activation
Divergent rays
from close object
Inverted
image
(b) Lens bulges for close vision. Parasympathetic
input contracts the ciliary muscle, loosening the
ciliary zonule, allowing the lens to bulge.
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Figure 15.13b
Problems of Refraction
• Myopia (nearsightedness)—focal point in front of
retina
• Hyperopia (farsightedness)—focal point behind retina
• Astigmatism—caused by unequal curvatures in
different parts of the cornea or lens
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Emmetropic eye (normal)
Focal
plane
Focal point is on retina.
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Figure 15.14 (1 of 3)
Myopic eye (nearsighted)
Eyeball
too long
Uncorrected
Focal point is in front of retina.
Corrected
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Concave lens moves focal
point further back.
Hyperopic eye (farsighted)
Eyeball
too short
Uncorrected
Focal point is behind retina.
Corrected
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Convex lens moves focal
point forward.
Figure 15.14 (3 of 3)
Functional Anatomy of Photoreceptors
• Rods and cones
• Outer segment of each contains visual
pigments -molecules that change shape as
they absorb light
• Once light is absorbed by the visual pigments,
this leads to a series of chemical reactions
which results in an AP along the optic nerve
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Process of
bipolar cell
Synaptic terminals
Rod cell body
Pigmented layer
Outer segment
Inner
segment
Nuclei
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Discs containing
visual pigments
Melanin
granules
(border
with choroid)
In the dark
Na+
Ca2+
Photoreceptor
cell (rod)
Ca2+
Bipolar
cell
7 No action potentials occur
along the optic nerve.
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Ganglion
cell
In the Light
Na+
Ca2+
Photoreceptor
cell (rod)
Ca2+
Bipolar
cell
7 Action potentials occur
along the optic nerve.
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Ganglion
cell
The Visual Pathway
Axons of ganglion cells form the Optic Nerve
Optic chiasma
optic tracts
thalamus
primary visual cortex in
the occipital lobe of the brain
conscious perception of the
image
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Fixation point
Right eye
Left eye
Optic nerve
Optic chiasma
Optic tract
thalamus
Occipital lobe
(primary visual cortex)
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HEARING AND BALANCE
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The Ear
• Three parts of the ear
1. External ear
2. Middle ear
3. Internal ear
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The Ear: Hearing and Balance
• External and middle ear are involved with:
hearing only
• Internal ear (labyrinth) functions in both:
hearing and equilibrium
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External
ear
Middle Internal ear
ear
(labyrinth)
Auricle
(pinna)
Helix
Lobule
External
Tympanic Pharyngotympanic
acoustic
membrane (auditory) tube
meatus
(a) The three regions of the ear
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Figure 15.25a
External Ear
• The auricle (pinna) is composed of:
• Helix (rim)
• Lobule (earlobe)
• External acoustic meatus (auditory canal)
• Short, curved tube lined with skin bearing
hairs, and ceruminous glands
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Middle Ear
• Tympanic membrane (eardrum)
• Boundary between external and middle ear
• CT membrane that vibrates in response to
sound
• Transfers sound energy to bones of middle ear
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Middle Ear
• Pharyngotympanic tube—connects the middle
ear to the nasopharynx
• Equalizes pressure in the middle ear cavity
with the external air pressure
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Oval window
(deep to stapes)
Semicircular
canals
Malleus
Vestibule
Auditory Incus
ossicles
Stapes
Tympanic membrane
Vestibular
nerve
Cochlear
nerve
Cochlea
Round window
(b) Middle and internal ear
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Pharyngotympanic
(auditory) tube
Ear Ossicles
• Three small bones in middle ear cavity: the
malleus, incus, and stapes
• Transmit vibratory motion of the eardrum to
the oval window
• Tensor tympani and stapedius muscles
contract reflexively in response to loud sounds
to prevent damage to the hearing receptors
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Malleus
Superior
Epitympanic
Incus
recess
Lateral
Anterior
View
Pharyngotympanic tube
Tensor
tympani
muscle
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Tympanic
membrane
(medial view)
Stapes
Stapedius
muscle
Figure 15.26
Internal Ear
• Bony labyrinth
• Winding channels in the temporal bone
• Three parts: vestibule, semicircular canals,
and cochlea
• Filled with perilymph
• Series of membranous sacs within the bony
labyrinth
• Filled with endolymph
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Superior vestibular ganglion
Inferior vestibular ganglion
Temporal
bone
Semicircular
ducts in
semicircular
canals
Facial nerve
Vestibular
nerve
Anterior
Posterior
Lateral
Cochlear
nerve
Maculae
Cristae ampullares
in the membranous
ampullae
Spiral organ
(of Corti)
Cochlear
duct
in cochlea
Utricle in
vestibule
Saccule in
vestibule
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Stapes in
oval window
Round
window
Figure 15.27
Vestibule
• Central egg-shaped cavity of the bony labyrinth
• Contains two membranous sacs that:
• House equilibrium receptor regions called maculae
• Maculae respond to pull of gravity and changes in
head position (linear movment)
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Otolithic membrane
Kinocilium
Stereocilia
Hyperpolarization
Receptor
potential
Nerve impulses
generated in
vestibular fiber
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Depolarization
When hairs bend toward
the kinocilium, the hair
cell depolarizes, exciting
the nerve fiber, which
generates more frequent
action potentials.
When hairs bend away
from the kinocilium, the
hair cell hyperpolarizes,
inhibiting the nerve fiber,
and decreasing the action
potential frequency.
Figure 15.35
Semicircular Canals
• Three canals are oriented along all three
planes (x,y,z)
• Membranous semicircular ducts line each
canal
• Ampulla of each canal houses equilibrium
receptor region called the crista ampullaris
• Receptors respond to rotational movements of
the head
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Crista
ampullaris
Endolymph
Hair cell
Crista
ampullaris
(a) Anatomy of a crista ampullaris in a
semicircular canal
Cupula
(b) Scanning electron
micrograph of a
crista ampullaris
(200x)
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Supporting
cell
Equilibrium
• Impulses sent from the vestibule (maculae) or
from ampulla (crista ampullaris) travel along
the vestibular nerve which quickly merges
with the cochlear nerve to form the
vestibulocochlear nerve (CN #8)
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Temporal
bone
Semicircular
ducts in
semicircular
canals
Vestibular
nerve
Anterior
Posterior
Lateral
Cochlear
nerve
Maculae
Cristae ampullares
in the membranous
ampullae
Spiral organ
(of Corti)
Cochlear
duct
in cochlea
Utricle in
vestibule
Saccule in
vestibule
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Stapes in
oval window
Round
window
The Cochlea
• A spiral, conical, bony chamber
• Extends from the vestibule
• Contains the cochlear duct, which houses the
spiral organ (of Corti)
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Sound and the Cochlea
• Organ of Corti
• In cochlear duct which runs through center of
cochlea
• Has hair cells(nerve cells) and supporting cells
• Tectorial membrane- gel-like mass that cilia of
hair cells are embedded in
• Basilar membrane-fibrous “floor” of organ of
corti
• Bending of the cilia: excites hair cells
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Tectorial membrane
Inner hair cell
Hairs (stereocilia)
Afferent nerve
fibers
Outer hair cells
Supporting cells
Fibers of
cochlear
nerve
(c)
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Basilar
membrane
Figure 15.28c
Auditory ossicles
Malleus Incus Stapes
Cochlear nerve
Scala vestibuli
Oval
window Helicotrema
2
3
Scala tympani
Cochlear duct
Basilar
membrane
1
Tympanic
Round
membrane
window
(a) Route of sound waves through the ear
1 Sound waves vibrate
the tympanic membrane.
2 Auditory ossicles vibrate.
Pressure is amplified.
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3 Pressure waves created by
the stapes pushing on the oval
window move through fluid in
the scala vestibuli.
Sounds with frequencies
below hearing travel through
the helicotrema and do not
excite hair cells.
Sounds in the hearing range
go through the cochlear duct,
vibrating the basilar membrane
and deflecting hairs on inner
hair cells.
Figure 15.31a
Transmission of Sound to the Internal Ear
• Transmission of Sound to the Inner Ear
• Sound waves enter the external acoustic canal and cause
tympanic membrane to vibrate
• Ossicles vibrate and amplify the pressure at the oval
window
• Pressure waves move through perilymph
• Sounds in the hearing range go through the cochlear duct,
ultimately causing bending of hair cells
• Impulses from the cochlea pass: along the cochlear
nerve, which then merges with the vestibular nerve
(forming vestibulocochlear N.) that travels to the primary
auditory cortex in temporal lobe of brain
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Deafness
• Hearing loss can be temporary or permanent
• Common causes:
• Middle ear infections
• Conduction deafness
• Can be caused by:
• Impacted earwax
• Ruptured eardrum
• Middle ear inflammations
• Otosclerosis
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Deafness
• Nerve Deafness
• Can be caused by:
• Gradual loss of hair cells throughout life
• Single explosive loud noise
• Prolonged exposure to loud noise
• Degeneration of cochlear nerve, tumors in
auditory cortex, etc.
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Tinnitus
• Ringing or clicking sound in ears in the
absence of auditory stimuli
• One of the first symptoms of cochlear
degeneration
• Can be caused by middle ear inflammation
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