Anatomy and physiology of the earAnatomy and physiology of the ear

External earExternal ear

Pinna (auricle) & External auditory meatusPinna (auricle) & External auditory meatus

Function: LocalizationFunction: Localization

Middle earMiddle ear

Tympanic membrane, Tympanic membrane, middle ear cavity, & middle ear cavity, & ossicles (malleus, ossicles (malleus, incus, stapes)incus, stapes)

Function: Function: Compensating for Compensating for impedance mismatch impedance mismatch between air and fluidbetween air and fluid

Three main components of middle ear Three main components of middle ear transfer function transfer function

1.1. Area difference between tympanic Area difference between tympanic membrane and stapes footplatemembrane and stapes footplate

2.2. Ossicular level actionOssicular level action

3.3. Buckling movement of tympanic Buckling movement of tympanic membranemembrane

Inner earInner ear

Bony and Bony and membraneous membraneous labyrinth labyrinth

Vestibular system Vestibular system (Semicircular (Semicircular canals & Vestibule) canals & Vestibule)

Auditory system Auditory system (Cochlea)(Cochlea)

Macrostructure of cochleaMacrostructure of cochlea

Microstructure of cochleaMicrostructure of cochlea

Function of cochleaFunction of cochlea

Frequency analysis of incoming sound: Frequency analysis of incoming sound: Basilar membrane acts as a series of Basilar membrane acts as a series of bandpass filtersbandpass filters

Transduction of mechanical vibration to Transduction of mechanical vibration to electrochemical/neural impulses: Forward electrochemical/neural impulses: Forward transductiontransduction

Outer hair cells: Responsible for Outer hair cells: Responsible for cochlear cochlear amplifieramplifier (Backward transduction) (Backward transduction)

Pathways of soundPathways of sound

Air conduction (AC): Transmission through Air conduction (AC): Transmission through outer, middle, inner ear, and higher up.outer, middle, inner ear, and higher up.

Bone conduction (BC): Transmission that Bone conduction (BC): Transmission that stimulates the inner ear directly through stimulates the inner ear directly through mechanical vibration of the skull.mechanical vibration of the skull.

Normal hearing

Conductivehearing loss

Sensorineuralhearing loss

Mixedhearing loss

Outer ear Middle ear Inner ear Auditory nerve

Outer ear Middle ear Inner ear Auditory nerve

Outer ear Middle ear Inner ear Auditory nerve

Outer ear Middle ear Inner ear Auditory nerve

CONDUCTIVE SENSORINEURAL