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

Basic Parts of the Ear External ear: Hearing; terminates at eardrum 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

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. 19.20

Middle Ear Auditory or eustachian tube Opens into pharynx, equalizes pressure Ossicles: malleus, incus, stapes: transmit vibrations Oval window Fig. 19.21

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. 19.22

Structure of Cochlea Membranous labyrinth of cochlea Scala vestibuli (perilymph) Scala tympani (perilymph) Cochlear duct (endolymph) Fig. 19.27 Fig. 19.27

Structure of Cochlea Spiral organ (organ of Corti) Cochlear nerve Hair cells Stereocilia (microvilli) Tectorial membrane Cochlear nerve Fig. 19.27

Effect of Sound Waves on Cochlear Structures Fig. 19.28

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. 19.23

Vestibule in Maintaining Balance Fig. 19.24

Balance 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)

Crista Ampullaris and Balance Fig. 19.26

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

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.

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.

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