15-1

Lecture 16

Sense Organs II: The Ear

15-2

Basic Parts of the Ear

• External ear: Hearing; terminates at eardrum• Middle ear: Hearing; contains auditory ossicles• Inner ear: Hearing and balance; interconnecting fluid-filled

tunnels and chambers

Fig. 19.20

15-3

External Ear• Auricle or pinna: elastic cartilage• External auditory canal• Tympanic membrane

External ear Middle ear Inner ear

Auricle(pinna) External auditory canal

Elasticcartilage

Tympanicmembrane

Fig. 19.20

15-4

Middle Ear• Auditory or

eustachian tube– Opens into

pharynx, equalizes pressure

• Ossicles: malleus, incus, stapes: transmit vibrations

• Oval window

Fig. 19.21

15-5

Inner EarLabyrinth• Bony

– Cochlea: Hearing

– Vestibule: Balance

– Semicircular canals: Balance • Membranous

Fig. 19.22

Lymphs• Endolymph

– In membranous labyrinth

• Perilymph– Space between

membranous and bony labyrinth

15-6

Structure of Cochlea• Membranous labyrinth of

cochlea– Scala vestibuli (perilymph)

– Scala tympani (perilymph)

– Cochlear duct (endolymph)

Fig. 19.27

Fig. 19.27

15-7

Structure of Cochlea• Spiral organ (organ of

Corti)– Hair cells

• Stereocilia (microvilli)

– Tectorial membrane

• Cochlear nerve

Fig. 19.27

15-8

Effect of Sound Waves on Cochlear Structures

Fig.19.28

15-9

BalanceTwo structural and functional components of balance in inner ear

1. Stationary Position and Linear Movement of HeadStationary 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

15-10

Vestibule in Maintaining Balance

Fig. 19.24

15-11

Balance2.2. Rotational Movements Rotational Movements

of Headof Head– Evaluates movements

of head (i.e. angular acceleration)

– 3 semicircular canals• Ampulla

– Crista ampullaris

– Hair cells

– Cupula

Vestibular nerve + Cochlear nerve = Vestibulocochlear nerve (VIII)Fig. 19.25

15-12

Crista Ampullaris and Balance

Fig. 19.26

15-13

Review QuestionA 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

15-14

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.

15-15

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.

15-16

Questions?