Download Cochlear duct

THE SPECIAL SENSES
Hearing and Equilibrium
THE EAR
 The organ of hearing and equilibrium
 Cranial nerve VIII - Vestibulocochlear
 Regions
 External ear
 Middle ear
 Internal ear (labyrinth)
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
Figure 15.25a
Middle Ear
Malleus
Superior
Epitympanic
Incus
recess
Lateral
Anterior
View
Pharyngotympanic tube
Tensor
tympani
muscle
Copyright © 2010 Pearson Education, Inc.
Tympanic
membrane
(medial view)
Stapes
Stapedius
muscle
Figure 15.26
MIDDLE EAR
 Auditory tube
 Connects the middle ear to the nasopharynx
 Equalizes pressure
 Opens during swallowing and yawning
 Otitis media
INNER EAR
 Contains functional organs for hearing & equilibrium
 Bony labyrinth
 Membranous labyrinth
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
Stapes in
oval window
Round
window
Figure 15.27
INNER EAR - BONY LABYRINTH
 Three distinct regions
 Vestibule
 Gravity
 Head position
 Linear acceleration and deceleration
 Semicircular canals
 Angular acceleration and deceleration
 Cochlea
 Vibration
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
Stapes in
oval window
Round
window
Figure 15.27
INNER EAR
 The cochlea
 A spiral, conical, bony chamber
 Vestibular canal (scala vestibuli)
 Cochlear duct (scala media)
 Tympanic canal (scala tympani)
Modiolus
Cochlear nerve,
division of the
vestibulocochlear
nerve (VIII)
Spiral ganglion
Osseous spiral lamina
Vestibular membrane
Cochlear duct
(scala media)
(a)
Helicotrema
Figure 15.28a
INNER EAR
 Cavity of the cochlea is divided into 3 chambers
Vestibular canal (scala vestibuli)
Vestibular membrane
Cochlear duct (scala media)
Basilar membrane supporting Organ of Corti
Tympanic canal (scala tympani)
Vestibular membrane
Osseous spiral lamina
Tectorial membrane
Cochlear duct
(scala media;
contains
endolymph)
Scala
vestibuli
(contains
perilymph)
Spiral
ganglion
Stria
vascularis
Spiral organ
(of Corti)
Basilar
membrane
Scala tympani
(contains
perilymph)
(b)
Copyright © 2010 Pearson Education, Inc.
Figure 15.28b
Tectorial membrane
Organ of Corti
Hairs (stereocilia)
Inner hair cell
Afferent nerve
fibers
Outer hair cells
Supporting cells
Fibers of
cochlear
nerve
(c)
Basilar
membrane
Figure 15.28c
PHYSIOLOGY OF HEARING
 Transduction of sound
Mechanical energy in middle ear
Fluid pressure wave in inner ear
Nerve impulse
PHYSIOLOGY OF HEARING IN A NUTSHELL
Sounds set up vibrations in air that beat against the eardrum
that pushes a chain of tiny bones that press fluid in the
internal ear against membranes that set up shearing forces
that pull on the tiny hair cells that stimulate nearby neurons
that give rise to the impulses that travel to the brain – and
you hear.
(This is from your textbook)
Air pressure
Wavelength
Area of
high pressure
(compressed
molecules)
Area of
low pressure
(rarefaction)
Crest
Trough
Distance
Amplitude
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.
Figure 15.29
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.
Copyright © 2010 Pearson Education, Inc.
Figure 15.30
Malleus Incus
Stapes vibrating Helicotrema
in oval window
Cochlea
Sound waves
Perilymph
3
7
4
5
1
2
6
9
External auditory
canal
8
Scala
tympani
Scala
vestibuli
Basilar
membrane
8
Spiral organ
(organ of Corti)
Tectorial membrane
Vestibular membrane
Cochlear duct
(contains endolymph)
Tympanic
membrane
Secondary tympanic
membrane vibrating
in round window
Middle ear
Auditory tube
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.
Copyright © 2010 Pearson Education, Inc.
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
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.
Copyright © 2010 Pearson Education, Inc.
Fibers of basilar membrane
Apex
(long,
floppy
fibers)
Base
(short,
stiff
fibers)
Frequency (Hz)
Figure 15.31b
Tectorial membrane
Inner hair cell
Hairs (stereocilia)
Afferent nerve
fibers
Outer hair cells
Supporting cells
Fibers of
cochlear
nerve
(c)
Copyright © 2010 Pearson Education, Inc.
Basilar
membrane
Figure 15.28c
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)
Figure 15.33
LOCALIZATION OF SOUND
 Timing comparison
 Side nearest sound detects sound first
 Comparison of volume
 High pitched = blocked by head
 Low pitched = curve around head
ABNORMALITIES OF HEARING
Conductive deafness
 Interference in movement of middle ear bones
 Impacted earwax, perforated eardrum or otosclerosis of the ossicles
Sensorineural deafness
 Damage to the neural structures
 Aging, prolonged exposure to loud sounds
ABNORMALITIES OF HEARING
Otitis media
ABNORMALITIES OF HEARING
Otosclerosis
ABNORMALITIES OF HEARING
Meniere’s Disease
ABNORMALITIES OF HEARING
Tinnitus
PHYSIOLOGY OF EQUILIBRIUM
 Information about position and movement of head
 Vestibular apparatus
 Utricle
Vesibule
 Saccule
 Semi-circular canals
Vestibular Apparatus
Kinocilium
Stereocilia
Otoliths
Otolithic
membrane
Hair bundle
Macula of
utricle
Macula of
saccule
Hair cells
Maculae are
perpendicular
to one another
Supporting
cells
Vestibular
nerve fibers
Figure 15.34
VESTIBULE
Macula
Utricle
 Horizontal movements
 Tilting the head side to side
Saccule
 Vertical movements
SEMI-CIRCULAR CANALS
 Crista ampullaris
 Sensory receptor for dynamic equilibrium
 One in the ampulla of each semicircular canal
 Major stimuli are rotatory movements
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
Supporting
cell
Cupula
(b) Scanning electron
micrograph of a
crista ampullaris
(200x)
Copyright © 2010 Pearson Education, Inc.
Figure 15.36a–b
MOTION SICKNESS
 Conflicts between eye movements and equilibrium
 Nystagmus
 Slow component
 Fast component
QUESTIONS?