1. Sense Organs II: The Ear
Lecture 16
Sense Organs II: The Ear

2. Basic Parts of the Ear External ear: Hearing; terminates at eardrum
Fig
External ear: Hearing; terminates at eardrum
Middle ear: Hearing; contains auditory ossicles
Inner ear: Hearing and balance; interconnecting fluid-filled tunnels and chambers

3. External Ear Auricle or pinna: elastic cartilage
External auditory canal
Tympanic membrane
External ear
Middle ear
Inner ear
Auricle
(pinna)
External auditory canal
Tympanic
membrane
Elastic
cartilage
Fig

4. Middle Ear Auditory or eustachian tube
Opens into pharynx, equalizes pressure
Ossicles: malleus, incus, stapes: transmit vibrations
Oval window
Fig

5. Inner Ear Labyrinth Lymphs Bony Endolymph Perilymph Membranous
Cochlea: Hearing
Vestibule: Balance
Semicircular canals: Balance
Membranous
Lymphs
Endolymph
In membranous labyrinth
Perilymph
Space between membranous and bony labyrinth
Fig

6. Structure of Cochlea Membranous labyrinth of cochlea
Scala vestibuli (perilymph)
Scala tympani (perilymph)
Cochlear duct (endolymph)
Fig
Fig

7. Structure of Cochlea Spiral organ (organ of Corti) Cochlear nerve
Hair cells
Stereocilia (microvilli)
Tectorial membrane
Cochlear nerve
Fig

8. Effect of Sound Waves on Cochlear Structures
Fig.
19.28

9. Balance
Two structural and functional components of balance in inner ear
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

10. Vestibule in Maintaining Balance
Fig

11. Balance Rotational Movements of Head
Evaluates movements of head (i.e. angular acceleration)
3 semicircular canals
Ampulla
Crista ampullaris
Hair cells
Cupula
Fig
Vestibular nerve + Cochlear nerve = Vestibulocochlear nerve (VIII)

12. Crista Ampullaris and Balance
Fig

13. 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
Bending of the microvilli of the spiral organ
Movement of perilymph fluid in the vestibule
Movement of the gelatinous covering over the maculae
Movement of endolymph fluid in the semicircular canals
Movement of the cupula

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. 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.

16. Questions?