Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chapter 15 The Special Senses The Ear

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Ear: Hearing and Balance  The ear is composed of three parts:  The outer ear :  Involved with hearing  The middle ear :  Involved with hearing  The inner ear:  Involved with hearing & equilibrium  Receptors for hearing and balance:  Respond to separate stimuli  Are activated independently

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Ear: Hearing and Balance Figure 15.25a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Outer Ear  The auricle (pinna) is composed of:  The helix (rim)  The lobule (earlobe)  External auditory canal  Short, curved tube  Filled with ceruminous glands

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Outer Ear  Tympanic membrane (eardrum)  Thin connective tissue membrane  Vibrates in response to sound  Transfers sound energy to the middle ear ossicles  Forms boundary between outer and middle ears

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Ear: Hearing and Balance Figure 15.25a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Middle Ear (Tympanic Cavity)  A small, air-filled, mucosa-lined cavity  Flanked laterally by the eardrum  Flanked medially by a bony wall with:  oval (vestibular) window  round (choclear) windows  Epitympanic recess:  Superior portion of the middle ear cavity  Pharyngotympanic tube:  Connects the middle ear to the nasopharynx  Equalizes pressure between middle ear cavity & external air

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Middle and Internal Ear Figure 15.25b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Middle Ear: Ear Ossicles  The tympanic cavity contains three small bones:  The malleus  The incus  The stapes  They transmit vibratory motion of the eardrum to the oval window  Strong vibrations are dampened by the:  Tensor tympani muscle (tenses eardrum medially)  Stapedius muscle (check oscicle vibration)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Middle Ear: Ear Ossicles Figure 15.26

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Inner Ear (Labyrinth)  Has two main divisions:  Bony labyrinth: Tortuous channels in the temporal bone  Contains the vestibule, the cochlea, and the semicircular canals  Filled with perilymph  Membranous labyrinth  Series of membranous sacs within the bony labyrinth  Filled with a potassium-rich fluid

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Inner Ear Figure 15.27

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Vestibule  The central egg-shaped cavity of the bony labyrinth  Suspended in its perilymph are two sacs:  the utricle  the saccule  The utricle extends into the semicircular canals  The saccule extends into the cochlea  These sacs:  House equilibrium receptors called maculae  Respond to gravity & head position changes

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Vestibule Figure 15.27

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Semicircular Canals  Three bony canals; each define two-thirds of a circle  They are the anterior, lateral, & posterior canals  Each canal lies in one of the three planes of space  A corresponding membranous duct lines each canal  The ducts communicate anteriorly with the utricle  Each ducts has a swollen end called an ampulla  The ampulla houses an equilibrium receptor region called crista ampullaris  These receptors respond to angular (rotational) move- ments of the head

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Semicircular Canals Figure 15.27

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Cochlea  A spiral, conical, bony chamber that:  Extends from the anterior vestibule  Coils around a bony pillar called the modiolus  Contains the cochlear duct, which :  Ends blindly at the cochlear apex  Contains the organ of Corti (hearing receptor)

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Cochlea Figure 15.27

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Cochlea  The cochlear duct & the oseous spiral lamina divides the cochlear cavity into three separate chambers:  Scala vestibuli (superior cochlear bony cavity):  Continuous with the vestible & abuts the oval window  Scala media (middle, “the cochlear duct” ):  The cochlear duct itself  Scala tympani (inferior cochlear bony cavity):  Inferior to the cochlear duct & terminates at the round window

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Cochlea  The scala tympani terminates at the round window  The scala tympani and scala vestibuli are:  Parts of the choclear cavity  Filled with perilymph  Continuous with each other via the helicotrema  The scala media is the choclear duct itself  The scala media is filled with endolymph

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Cochlea  The “floor” of the cochlear duct is composed of:  The bony spiral lamina  The basilar membrane, which supports the organ of Corti  The cochlear branch of cranial nerve VIII runs from the organ of Corti to the brain

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Cochlea Figure 15.28

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Sound and Mechanisms of Hearing  Sound vibrations beat against the eardrum  The eardrum pushes against the ossicles  This presses fluid in the inner ear against the oval and round windows  This movement sets up shearing forces that pull on hair cells  Moving hair cells stimulates the cochlear nerve that sends impulses to the brain