Lecture 16
Sense Organs II: The Ear
15-1
Basic Parts of the Ear
Fig. 19.20
• External ear: Hearing; terminates at eardrum
• Middle ear: Hearing; contains auditory ossicles
• Inner ear: Hearing and balance; interconnecting fluid-filled
tunnels and chambers
15-2
External Ear
•
•
•
Auricle or pinna: elastic cartilage
External auditory canal
Tympanic membrane
External ear
Auricle
(pinna)
Inner ear
Middle ear
External auditory canal
Tympanic
membrane
Elastic
cartilage
Fig. 19.20
15-3
Middle Ear
• Auditory or
eustachian tube
– Opens into
pharynx,
equalizes pressure
• Ossicles: malleus,
incus, stapes:
transmit vibrations
• Oval window
Fig. 19.21
15-4
Labyrinth
Inner Ear
• Bony
– Cochlea: Hearing
– Vestibule: Balance
– Semicircular canals: Balance
• Membranous
Lymphs
• Endolymph
– In membranous
labyrinth
• Perilymph
– Space between
membranous
and bony
labyrinth
Fig. 19.22
15-5
Structure of Cochlea
•
Membranous labyrinth of
cochlea
–
–
–
Scala vestibuli (perilymph)
Scala tympani (perilymph)
Cochlear duct (endolymph)
Fig. 19.27
Fig. 19.27
15-6
Structure of Cochlea
•
Spiral organ (organ of
Corti)
–
–
•
Hair cells
• Stereocilia (microvilli)
Tectorial membrane
Cochlear nerve
Fig. 19.27
15-7
Effect of Sound Waves on
Cochlear Structures
Fig.
19.28
15-8
Balance
Two structural and functional components of balance in inner ear
1. Stationary Position and Linear Movement of Head
• Evaluates position of head relative to gravity
• Detects linear acceleration and deceleration
• Utricle and saccule
–
Maculae: Consist of hair cells embedded in statoconic membrane
containing otoliths
Fig. 19.23
15-9
Vestibule in Maintaining Balance
Fig. 19.24
15-10
Balance
2. Rotational Movements
of Head
– Evaluates movements
of head (i.e. angular
acceleration)
– 3 semicircular canals
•
Ampulla
– Crista ampullaris
– Hair cells
– Cupula
Fig. 19.25
Vestibular nerve + Cochlear nerve = Vestibulocochlear nerve (VIII)
15-11
Crista Ampullaris and Balance
Fig. 19.26
15-12
Review Question
A person driving a car along a straight street suddenly sees an
animal dart in front of the car. He slams on the brakes and
manages to stop in time. The sensation of rapid deceleration is
generated by the
(a) Bending of the microvilli of the spiral organ
(b) Movement of perilymph fluid in the vestibule
(c) Movement of the gelatinous covering over the maculae
(d) Movement of endolymph fluid in the semicircular canals
(e) Movement of the cupula
15-13
Points to Remember
• Inner ear functions for hearing and balance.
• Sound waves enter the external auditory canal,
impact tympanic membrane, vibrate middle ear
ossicles, strike oval window, create waves in
perilymph of scala vestibuli, increase pressure in
endolymph in cochlear duct, membrane supporting
hair cells vibrates, hair cells stimulated, vibrations
transferred to perilymph of scala tympani, travel to
round window and dampened.
15-14
Points to Remember
• Static balance is orientation of body relative to
pull of gravity - maculae of utricle and saccule
(static labyrinth) are sense organs of static
balance.
• Kinetic balance is maintenance of body position in
response to movement - crista ampullaris in
semicircular canals (kinetic labyrinth) are sense
organs of kinetic balance.
15-15
Questions?
15-16