Anatomy and physiology of the ear External ear

Anatomy and physiology of the ear

External ear l Pinna (auricle) & External auditory meatus l Function: Localization

Middle ear l Tympanic membrane, middle ear cavity, & ossicles (malleus, incus, stapes) l Function: Compensating for impedance mismatch between air and fluid

Three main components of middle ear transfer function 1. Area difference between tympanic membrane and stapes footplate 2. Ossicular level action 3. Buckling movement of tympanic membrane

Inner ear l Bony and membraneous labyrinth l Vestibular system (Semicircular canals & Vestibule) l Auditory system (Cochlea)

Macrostructure of cochlea

Microstructure of cochlea

Function of cochlea l Frequency analysis of incoming sound: Basilar membrane acts as a series of bandpass filters l Transduction of mechanical vibration to electrochemical/neural impulses: Forward transduction l Outer hair cells: Responsible for cochlear amplifier (Backward transduction)

Pathways of sound l Air conduction (AC): Transmission through outer, middle, inner ear, and higher up. l Bone conduction (BC): Transmission that stimulates the inner ear directly through mechanical vibration of the skull.

CONDUCTIVE SENSORINEURAL Normal hearing Outer ear Middle ear Inner ear Auditory nerve Conductive hearing loss Outer ear Middle ear Inner ear Auditory nerve Sensorineural hearing loss Outer ear Middle ear Inner ear Auditory nerve Mixed hearing loss Outer ear Middle ear Inner ear Auditory nerve