AUDITORY SYSTEM: Anatomy, physiology and function Chunfu Dai,m.d&PhD Otolaryngology Department Fudan University
Outer Middle Inner Bor Stapes Semicircular Malleus Oval Concha window The ear is divided into three parts Vestibular Outer, Midd Cochlear and nner ear nerve Cochlea Each serves different Vestibule aspects of the Round window auditory sensation The outer ear is collects sound waves Pinna and directs them towards the middle External ear auditory meatus Outer/ Middle Inner collection transformation \transduction
The ear is divided into three parts: Outer, Middle, and Inner ear. Each serves different aspects of the auditory sensation. The outer ear is collects sound waves and directs them towards the middle ear Outer Middle Inner collection transformation transduction Outer Middle Inner
Sound waves in the ear canal vibrate Ear oSsicles is of rotation the ear drum oscillating the middle ear bones. Thus, the oscillations of the ear drum are conveyed to the oval window at the base of the cochlea tympanic Malleus Incus Stapes small force LARGE FORCE LARGE AMPLITUDE small amplitude Middle ear bones act an impedance matcher, enabling sound pressure waves in air to be introduced into the fluid-filled inner ear at the oval window. at the base of the cochlea Tympanic Round Base of stapes membrane window In oval window
Sound waves in the ear canal vibrate the ear drum, oscillating the middle ear bones. Thus, the oscillations of the ear drum are conveyed to the oval window at the base of the cochlea Middle ear bones act an impedance matcher, enabling sound pressure waves in air to be introduced into the fluid-filled inner ear at the oval window, at the base of the cochlea
The Inner ear is a bony labyrinth, and contains the cochlea and the vestibular system Cochlear Receptors -Cochlear nerve Semicircular A Membranous Utricle canals labyrinth within bony labyrinth Sacco le path of sound waves Scala vestibuli Cochlear duct (scala media Scala tympani Round window Oval window and stapes Vibration of the stapes at the oval window results in pressure waves that travel through the cochlear fluids until they reach the round window
Vibration of the stapes at the oval window results in pressure waves that travel through the cochlear fluids until they reach the round window The Inner ear is a bony labyrinth, and contains the cochlea and the vestibular system
The membranous labyrinth partitions the bony labyrinth of the cochlea into three chambers-the perilymphatic scala vestibuli and scala tympani; and the endolymphatic scala media. These fluids also extend into the vestibular labyrinth Vestibular Apical turn membrane Tectorial membrane Middle turn Vestibular duct Modiolus (scala vestibuli- contaIns From perilymph) Cochlear duct scala media- contains Basal endolymph) turn Organ of Corti Tympanic F。e tympani membrane s contains To round perilymph) window Temporal bone Spiral ganglion (petrous portion) Cochlear nerve Vestibulocochlear nerve(N VIll)
The membranous labyrinth partitions the bony labyrinth of the cochlea into three chambers – the perilymphatic scala vestibuli and scala tympani; and the endolymphatic scala media. These fluids also extend into the vestibular labyrinth
Vibrations of the stapes at the Vestibular nerve oval window induces fluid Auditory nerve pressure waves in the cochlea fluids Oval Cross section of cochlea window Round Scala Tectorial media window Cochlea membrane Scala vestibuli Spiral lio this pi Scala tympani Inner hair cells Outer membrane
Vibrations of the stapes at the oval window induces fluid pressure waves in the cochlea fluids. QuickTime™ and a Animation decompressor are needed to see this picture
Sound waves enter the scala vestibuli, pass through the scala media at some point in their course to the scala tympani and round window, oscillating the basilar membrane QuickTime and leede m tensor tympan m stapedius Vestibule Oval window Scala media of malleus ess of incus Helicotrema membranc ,· Cochlear partition stapedial joint 2.crus stapes Scala tympani footplate Round window Eustachian tube
Sound waves enter the scala vestibuli, pass through the scala media at some point in their course to the scala tympani and round window, oscillating the basilar membrane. QuickTime™ and a Animation decompressor are needed to see this picture
Pressure waves in the scala vestibuli are conducted through ( bi Direction of wave propagation the scala media and into the scala tympani at the point of maximum deflection of the basilar membrane. This sets up a traveling wave in the basilar Base: Basilar membrane membrane, high frequency at the is narrow and stiff Apex base, low frequency at the apex BM is wide and compliant Relative 1600Hz Basilar membrane 800H Scala vestibuli Cochlear base 200Hz 100Hz Scala mani Unrolled Tympanic Narrow base of Distance from membrane basilar membrane Wider apex is Cochlear Helicotrema stapes(mn Stapes on is"tuned"for high,"tuned"for apex oval window frequencies low frequencies Thus the basilar membrane is tonotopically organized
Pressure waves in the scala vestibuli are conducted through the scala media and into the scala tympani at the point of maximum deflection of the basilar membrane. This sets up a traveling wave in the basilar membrane, high frequency at the base, low frequency at the apex. Apex: BM is wide and compliant Base: Basilar membrane is narrow and stiff Thus the basilar membrane is tonotopically organized
Traveling W ave behavior of QuickTime and a are needed to see this picture the basilar membrane The traveling wave appears to move to the right(cochlear apex This is an illusion. High frequencies vibrate more frequently higher amplitudes, thus displacement of the basilar h over time than low frequencies, while low frequencies lave membrane in response to a single click(broadband noise) “ appears”" to move to the right
QuickTime™ and a Cinepak decompressor are needed to see this picture
In order to sense the oscillations of the basilar membrane. we must introduce a sensory receptor, the hair cell