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CHAPTER 15
THE SPECIAL SENSES
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THE SPECIAL SENSES
Overview
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Which of these is NOT a special sense?
1)
2)
3)
4)
5)
touch
sight
taste
smell
hearing
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THE SPECIAL SENSES
VISION
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Figure 15.1b The eye and associated accessory structures.
Levator palpebrae
superioris muscle
Orbicularis oculi muscle
Eyebrow
Tarsal plate
Palpebral conjunctiva
Tarsal glands
Cornea
Palpebral fissure
Eyelashes
Bulbar conjunctiva
Conjunctival sac
Orbicularis oculi muscle
(b) Lateral view; some structures shown in sagittal section
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Figure 15.2 The lacrimal apparatus.
Lacrimal sac
Lacrimal gland
Excretory ducts
of lacrimal glands
Lacrimal punctum
Lacrimal canaliculus
Nasolacrimal duct
Inferior meatus
of nasal cavity
Nostril
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Figure 15.3a Extrinsic eye muscles.
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 15.3b Extrinsic eye muscles.
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 15.4a Internal structure of the eye (sagittal section).
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 15.4b Internal structure of the eye (sagittal section).
Ciliary body
Ciliary
processes
Iris
Margin
of pupil
Anterior
segment
Lens
Cornea
Ciliary zonule
(suspensory
ligament)
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Vitreous humor
in posterior
segment
Retina
Choroid
Sclera
Fovea centralis
Optic disc
Optic nerve
(b) Photograph of the human eye.
Which layer of the eye contains photoreceptors?
1) sclera
2) choroid
3) retina
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Quiz Q4: Which nerve controls the muscles
that move the eyeball?
1)
2)
3)
4)
Vagus nerve
Phrenic nerve
Oculomotor nerve
Sciatic nerve
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Quiz Q5: True or false: Tears are produced
In the medial corner of the eye.
1) True
2) False
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Figure 15.5 Pupil dilation and constriction, anterior view.
Parasympathetic +
Sphincter pupillae
muscle contraction
decreases pupil size.
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Sympathetic +
Iris (two muscles)
• Sphincter pupillae
• Dilator pupillae
Dilator pupillae
muscle contraction
increases pupil size.
Figure 15.6a Microscopic anatomy of the retina.
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 15.6b Microscopic anatomy of the retina.
Ganglion
cells
Bipolar
cells
Amacrine cell
Photoreceptors
• Rod
• Cone
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 15.6c Microscopic anatomy of the retina.
Nuclei of
ganglion
cells
Outer segments
of rods and cones
Nuclei
Axons of
Nuclei of
of
bipolar
ganglion
rods and
cells
cells
cones
(c) Photomicrograph of retina
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Choroid
Pigmented
layer of retina
A neuron which receives information from a
rod or cone and passes it to another neuron
is called a…
1)
2)
3)
4)
5)
Photoreceptor
Retina cell
Bipolar cell
Ganglion cell
Optic nerve cell
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Figure 15.7 Part of the posterior wall (fundus) of the right eye as seen with an ophthalmoscope.
Central
artery
and vein
emerging
from the
optic disc
Macula
lutea
Optic disc
Retina
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Figure 15.8 Circulation of aqueous humor.
Cornea
Lens
Iris
Lens
epithelium
Lens
Cornea
Corneal epithelium
Corneal endothelium
Aqueous humor
Anterior Anterior
segment chamber
(contains Posterior
aqueous
chamber
3
humor)
Scleral venous
sinus
1 Aqueous humor is
Cornealformed by filtration
scleral junction
2
from the capillaries in
the ciliary processes.
Bulbar
2 Aqueous humor flows from the
conjunctiva
posterior chamber through the pupil
Sclera
into the anterior chamber. Some also
flows through the vitreous humor
(not shown).
3 Aqueous humor is reabsorbed into the
venous blood by the scleral venous sinus.
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Posterior
segment
(contains
vitreous
humor)
Ciliary zonule
(suspensory
ligament)
1
Ciliary
processes
Ciliary
muscle
Ciliary
body
Figure 15.9 Photograph of a cataract.
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Figure 15.10 The electromagnetic spectrum and photoreceptor sensitivities.
Gamma
rays
X rays
UV
Infrared
MicroRadio waves
waves
(a)
Light absorption (pervent of maximum)
Visible light
(b)
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Blue
cones
(420 nm)
Green Red
cones cones
Rods
(500 nm) (530 nm) (560 nm)
Wavelength (nm)
Figure 15.11 Refraction.
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Figure 15.12 Bending of light by a convex lens.
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 15.13a Focusing for distant and close vision.
Sympathetic activation
Nearly parallel rays
from distant object
Lens
Ciliary zonule
Ciliary muscle
Inverted
image
(a) Lens is flattened for distant vision. Sympathetic
input relaxes the ciliary muscle, tightening the ciliary
zonule, and flattening the lens.
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Figure 15.13c Focusing for distant and close vision.
View
Ciliary muscle
Lens
Ciliary zonule
(suspensory ligament)
(c) The ciliary muscle and ciliary zonule are
arranged sphincterlike around the lens.
(Anterior segment as viewed from within the eye.)
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Figure 15.13b Focusing for distant and close vision.
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 15.14 Problems of refraction (1 of 3).
Emmetropic eye (normal)
Focal
plane
Focal point is on retina.
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Figure 15.14 Problems of refraction (2 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.
Figure 15.14 Problems of refraction (3 of 3).
Hyperopic eye (farsighted)
Eyeball
too short
Uncorrected
Focal point is behind retina.
Corrected
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Convex lens moves focal
point forward.
An image of an object is presented ________
on the retina.
1)
2)
3)
4)
Upside down and mirror image
Upside down and reversed
Right side up and mirror image
Right side up and reversed
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A myopic person cannot see distant images
well because…
1)
2)
3)
4)
Their eyeball is too long
Their eyeball is too short
Their eyeball is too wide
Their eyeball is too narrow
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Figure 15.15a Photoreceptors of the retina.
Process of
bipolar cell
Synaptic terminals
Rod cell body
Rod cell body
Cone cell body
Nuclei
Outer fiber
Mitochondria
(a) The outer segments
of rods and cones
are embedded in the
pigmented layer of
the retina.
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Pigmented layer
Outer segment
Inner
segment
Inner fibers
Connecting
cilia
Apical microvillus
Melanin
granules
Discs containing
visual pigments
Discs being
phagocytized
Pigment cell nucleus
Basal lamina (border
with choroid)
Figure 15.15b Photoreceptors of the retina.
Rod discs
Visual
pigment
consists of
• Retinal
• Opsin
(b) Rhodopsin, the visual pigment in rods, is embedded in
the membrane that forms discs in the outer segment.
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Figure 15.16 The formation and breakdown of rhodopsin.
11-cis-retinal
1 Bleaching of
2H+
Oxidation
Vitamin A
11-cis-retinal
Rhodopsin
Reduction
2H+
2 Regeneration
of the pigment:
Enzymes slowly
convert all-trans
retinal to its
11-cis form in the
pigmented
epithelium;
requires ATP.
Dark
Light
Opsin and
All-trans-retinal
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the pigment:
Light absorption
by rhodopsin
triggers a rapid
series of steps
in which retinal
changes shape
(11-cis to all-trans)
and eventually
releases from
opsin.
All-trans-retinal
Figure 15.17 Events of phototransduction.
1
Light (photons)
activates visual pigment.
Visual
pigment
Phosphodiesterase (PDE)
All-trans-retinal
Light
Open
cGMP-gated
cation
channel
11-cis-retinal
Transducin
(a G protein)
2
Visual pigment activates
transducin
(G protein).
3
Transducin
activates
phosphodiester
ase (PDE).
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4
PDE converts
cGMP into GMP,
causing cGMP
levels to fall.
5
Closed
cGMP-gated
cation
channel
As cGMP levels
fall, cGMP-gated
cation channels
close, resulting in
hyperpolarization.
Figure 15.18 Signal transmission in the retina (1 of 2).
In the dark
1 cGMP-gated channels
open, allowing cation influx;
the photoreceptor
depolarizes.
Na+
Ca2+
Photoreceptor
cell (rod)
2 Voltage-gated Ca2+
channels open in synaptic
terminals.
3 Neurotransmitter is
released continuously.
Ca2+
4 Neurotransmitter causes
IPSPs in bipolar cell;
hyperpolarization results.
5 Hyperpolarization closes
voltage-gated Ca2+ channels,
inhibiting neurotransmitter
release.
6 No EPSPs occur in
ganglion cell.
7 No action potentials occur
along the optic nerve.
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Bipolar
cell
Ganglion
cell
Figure 15.18 Signal transmission in the retina (2 of 2).
In the light
1 cGMP-gated channels
are closed, so cation influx
stops; the photoreceptor
hyperpolarizes.
Light
Photoreceptor
cell (rod)
2 Voltage-gated Ca2+
channels close in synaptic
terminals.
3 No neurotransmitter
is released.
4 Lack of IPSPs in bipolar
cell results in depolarization.
5 Depolarization opens
voltage-gated Ca2+ channels;
neurotransmitter is released.
Bipolar
cell
Ca2+
Ganglion
cell
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6 EPSPs occur in ganglion
cell.
7 Action potentials
propagate along the
optic nerve.
The protein responsible for detecting light
in rods is…
1)
2)
3)
4)
Vitamin A
photoreceptor
11-cis-retinal
rhodopsin
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True or False: Photoreceptors generate action
potentials when they are stimulated by light.
1) True
2) False
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Figure 15.19a Visual pathway to the brain and visual fields, inferior view.
Fixation point
Right eye
Suprachiasmatic
nucleus
Pretectal nucleus
Lateral geniculate
nucleus of
thalamus
Superior colliculus
Left eye
Optic nerve
Optic chiasma
Optic tract
Uncrossed (ipsilateral) fiber
Crossed (contralateral) fiber
Optic radiation
Occipital lobe
(primary visual cortex)
(a) The visual fields of the two eyes overlap considerably.
Note that fibers from the lateral portion of each retinal field do
not cross at the optic chiasma.
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Figure 15.19b Visual pathway to the brain and visual fields, inferior view.
Optic nerve
Optic chiasma
Optic tract
Lateral geniculate
nucleus
Superior colliculus
(sectioned)
Optic radiation
Corpus callosum
(b) Photograph of human brain, with the right side
dissected to reveal internal structures.
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Which of the following structures is not involved
in the processing of visual information?
1)
2)
3)
4)
Retina
Thalamus
Medulla oblongata
Visual cortex in occipital lobe
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THE SPECIAL SENSES
OLFACTION (SMELL)
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Figure 15.21a Olfactory receptors.
Olfactory
epithelium
Olfactory tract
Olfactory bulb
Nasal
conchae
(a)
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Route of
inhaled air
Figure 15.21b Olfactory receptors.
Olfactory
tract
Mitral cell (output cell)
Glomeruli
Olfactory bulb
Cribriform plate of ethmoid bone
Filaments of olfactory nerve
Olfactory
gland
Lamina propria connective tissue
Axon
Basal cell
Olfactory receptor cell
Olfactory
epithelium
Supporting cell
Mucus
(b)
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Dendrite
Olfactory cilia
Route of inhaled air
containing odor molecules
Figure 15.22 Olfactory transduction process.
1
Odorant binds
to its receptor.
Odorant
Adenylate cyclase
G protein (Golf)
Open
cAMP-gated
cation channel
Receptor
GDP
2
Receptor
activates G
protein (Golf).
3
G protein
activates
adenylate
cyclase.
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4
Adenylate
cyclase converts
ATP to cAMP.
5 cAMP opens a
cation channel allowing
Na+ and Ca2+ influx and
causing depolarization.
THE SPECIAL SENSES
GUSTATION (TASTE)
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Figure 15.23 Location and structure of taste buds on the tongue.
Foliate papillae
Epiglottis
Connective
tissue
Taste fibers
of cranial
nerve
Gustatory
hair
Palatine tonsil
Lingual tonsil
Circumvallate
papilla
Fungiform
papillae
(a) Taste buds are
associated with
fungiform, foliate,
and circumvallate
(vallate) papillae.
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Stratified
Basal Gustatory Taste squamous
cells (taste) cells pore epithelium
of tongue
Taste bud
(b) Enlarged section
of a circumvallate
papilla.
(c) Enlarged view of a taste bud.
Figure 15.23a Location and structure of taste buds on the tongue.
Epiglottis
Palatine tonsil
Lingual tonsil
Foliate papillae
Fungiform papillae
(a) Taste buds are associated with fungiform,
foliate, and circumvallate (vallate) papillae.
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Figure 15.23b Location and structure of taste buds on the tongue.
Circumvallate papilla
Taste bud
(b) Enlarged section of a
circumvallate papilla.
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Figure 15.23c Location and structure of taste buds on the tongue.
Connective
tissue
Taste fibers
of cranial
nerve
Gustatory
hair
Basal Gustatory Taste
cells (taste) cells pore
Stratified
squamous
epithelium
of tongue
(c) Enlarged view of a taste bud.
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Figure 15.24 The gustatory pathway.
Gustatory cortex
(in insula)
Thalamic nucleus
(ventral posteromedial
nucleus)
Pons
Solitary nucleus in
medulla oblongata
Facial nerve (VII)
Glossopharyngeal
nerve (IX)
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Vagus nerve (X)
Gustation and olfaction use what kind of
sensory receptors?
1)
2)
3)
4)
5)
Mechanoreceptors
Chemoreceptors
Photoreceptors
Nociceptors
Thermoreceptors
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THE SPECIAL SENSES
HEARING & EQUILIBRIUM (BALANCE)
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Figure 15.25a Structure of the ear.
External
ear
Middle Internal ear
ear
(labyrinth)
Auricle
(pinna)
Helix
Lobule
External
acoustic
meatus
(a) The three regions of the ear
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Tympanic Pharyngotympanic
membrane (auditory) tube
Figure 15.25b Structure of the ear.
Oval window
(deep to stapes)
Entrance to mastoid
antrum in the
epitympanic recess
Auditory
ossicles
Malleus
(hammer)
Incu
(anvil)
Stapes
(stirrup)
Tympanic membrane
Semicircular
canals
Vestibule
Vestibular
nerve
Cochlear
nerve
Cochlea
Round window
(b) Middle and internal ear
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Pharyngotympanic
(auditory) tube
Figure 15.26 The three auditory ossicles and associated skeletal muscles.
Malleus
Superior
Epitympanic
recess
Incus
Lateral
Anterior
View
Pharyngotympanic tube
Tensor
tympani
muscle
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Tympanic
membrane
(medial view)
Stapes
Stapedius
muscle
The separation between the outer ear and
inner ear is the…
1)
2)
3)
4)
Auricle
Incus
Oval window
Tympanic membrane
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The spiral-shaped structure in the inner ear
which contains receptors for hearing is the…
1)
2)
3)
4)
vestibule
macula
cochlea
pharyngotympanic tube
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Figure 15.27 Membranous labyrinth of the internal ear.
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
Utricle in
vestibule
Saccule in
vestibule
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Stapes in
oval window
Spiral organ
(of Corti)
Cochlear
duct
in cochlea
Round
window
Figure 15.28a Anatomy of the cochlea.
Modiolus
Cochlear nerve,
division of the
vestibulocochlear
nerve (VIII)
Spiral ganglion
Osseous spiral lamina
Vestibular membrane
Cochlear duct
(scala media)
(a)
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Helicotrema
Figure 15.28b Anatomy of the cochlea.
Vestibular membrane
Tectorial membrane
Cochlear duct
(scala media;
contains
endolymph)
Osseous spiral lamina
Scala
vestibuli
(contains
perilymph)
Stria
vascularis
Spiral organ
(of Corti)
Basilar
membrane
(b)
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Scala tympani
(contains
perilymph)
Spiral
ganglion
Figure 15.28c Anatomy of the cochlea.
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 15.28d Anatomy of the cochlea.
Inner
hair
cell
Outer
hair
cell
(d)
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True or false: The organ of Corti senses
sound waves when the tectorial membrane
vibrates.
1) True
2) False
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The actual sensory receptor of hearing is the…
1)
2)
3)
4)
the cochlea
hair cell
the basilar membrane
the tympanic membrane
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Air pressure
Figure 15.29 Sound: source and propagation.
Wavelength
Area of
high pressure
(compressed
molecules)
Area of
low pressure
(rarefaction)
Crest
Trough
Distance
Amplitude
(a) A struck tuning fork alternately compresses
and rarefies the air molecules around it,
creating alternate zones of high and
low pressure.
(b) Sound waves
radiate outward
in all directions.
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Figure 15.30 Frequency and amplitude of sound waves.
Pressure
High frequency (short wavelength) = high pitch
Low frequency (long wavelength) = low pitch
Time (s)
(a) Frequency is perceived as pitch.
Pressure
High amplitude = loud
Low amplitude = soft
Time (s)
(b) Amplitude (size or intensity) is perceived as loudness.
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Figure 15.30a Frequency and amplitude of sound waves.
Pressure
High frequency (short wavelength) = high pitch
Low frequency (long wavelength) = low pitch
Time (s)
(a) Frequency is perceived as pitch.
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Figure 15.30b Frequency and amplitude of sound waves.
Pressure
High amplitude = loud
Low amplitude = soft
Time (s)
(b) Amplitude (size or intensity) is perceived
as loudness.
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The “pitch” of a sound is determined by…
1) amplitude of a sound wave
2) frequency of a sound wave
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Figure 15.31a Pathway of sound waves and resonance of the basilar membrane.
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
3 Pressure waves created by
the tympanic membrane.
the stapes pushing on the oval
window move through fluid in
the scala vestibuli.
2 Auditory ossicles vibrate.
Pressure is amplified.
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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 15.31b Pathway of sound waves and resonance of the basilar membrane.
Basilar membrane
High-frequency sounds displace
the basilar membrane near the base.
Medium-frequency sounds displace
the basilar membrane near the middle.
Low-frequency sounds displace the
basilar membrane near the apex.
(b) Different sound frequencies cross the
basilar membrane at different locations.
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Fibers of basilar membrane
Apex
(long,
floppy
fibers)
Base
(short,
stiff
fibers)
Frequency (Hz)
Figure 15.32 Photo of cochlear hair cell with its precise array of stereocilia.
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“Resonance” refers to…
1) Something really making sense
2) The vestibule and cochlea vibrating at the
same time and same frequency
3) The response of fibers of a particular
length vibration with sound waves of a
particular frequency.
4) Fibers of a particular length vibrating with
sound waves of a particular amplitude.
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Figure 15.33 The auditory pathway.
Medial geniculate
nucleus of thalamus
Primary auditory
cortex in temporal lobe
Inferior colliculus
Lateral lemniscus
Superior olivary nucleus
(pons-medulla junction)
Midbrain
Cochlear nuclei
Vibrations
Medulla
Vestibulocochlear nerve
Vibrations
Spiral ganglion of cochlear nerve
Bipolar cell
Spiral organ (of Corti)
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Which of these structures is NOT involved in
carrying information from the vestibulocochlear
nerve?
1)
2)
3)
4)
thalamus
Auditory cortex
pons
Medulla oblongata
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Figure 15.34 Structure of a macula.
Kinocilium
Stereocilia
Otoliths
Otolithic
membrane
Hair bundle
Macula of
utricle
Macula of
saccule
Hair cells
Supporting
cells
Vestibular
nerve fibers
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Figure 15.35 The effect of gravitational pull on a macula receptor cell in the utricle.
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 15.36a–b Location, structure, and function of a crista ampullaris in the internal ear.
Cupula
Crista
ampullaris
Endolymph
Hair bundle (kinocilium
plus stereocilia)
Hair cell
Crista
Membranous
ampullaris
labyrinth
Fibers of vestibular nerve
(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
Figure 15.36c Location, structure, and function of a crista ampullaris in the internal ear.
Section of
ampulla,
filled with
endolymph
Cupula
Fibers of
vestibular
nerve
At rest, the cupula stands
upright.
(c) Movement of the
cupula during
rotational
acceleration
and deceleration
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Flow of endolymph
During rotational acceleration,
endolymph moves inside the
semicircular canals in the
direction opposite the rotation
(it lags behind due to inertia).
Endolymph flow bends the
cupula and excites the hair
cells.
As rotational movement
slows, endolymph keeps
moving in the direction
of the rotation, bending
the cupula in the
opposite direction from
acceleration and
inhibiting the hair cells.
Rotational movement is detected by…
1) Macula in utricle
2) Macula in saccule
3) Cupula & crista ampullaris attached to
semicircular canals
4) All of the above
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Figure 15.37 Pathways of the balance and orientation system.
Input: Information about the body’s position in space comes
from three main sources and is fed into two major processing
areas in the central nervous system.
Cerebellum
Somatic receptors
(from skin, muscle
and joints)
Visual
receptors
Vestibular
receptors
Vestibular
nuclei
(in brain stem)
Central nervous
system processing
Oculomotor control
(cranial nerve nuclei
III, IV, VI)
Spinal motor control
(cranial nerve XI nuclei
and vestibulospinal tracts)
(eye movements)
(neck movements)
Output: Fast reflexive control of the muscles serving the eye
and neck, limb, and trunk are provided by the outputs of the
central nervous system.
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