Transcript Slide 1
EAC -2.5 cm long S-shaped curved anteriorly -lateral 1/3 cerumen cartilaginous -resonance at 3500 Hz, gain of 15 dB for adults *resonance is 8000Hz for baby until 2.5 years of age Innervation •Anteriorly auriculotemporal nerve V3 •posterior superior CN 7 •posterior inferior and floor CN 9 (Jacobsen) +10 (Arnold) •clockwise Head Shadow effect Head blocks sound Shorter wavelengths > 2000Hz can’t bend and will have interaural INTENSITY difference Longer wavelengths can bend around head and will have interaural TIME difference Middle ear must compensate for loss of energy from air to fluid transition (impedence) Impedence match Area of TM to area of footplate 17 : 1 Handle of malleus and long process of incus 1.3 : 1 Shape of TM allows difference in reception of oval and round window 22 : 1 advantage 25-30 dB gained Transformer ratio Cochleariform process houses tensor tympani which attaches to handle of malleus (CN V) and points to facial Stapedieus emanates from the pyrimidal process CN 7 Both are smallest striated mm of body Stapedial reflex is bilateral Protects cochlea esp. <2000Hz from sounds > 90dB Delay of 10 ms COCHLEA 2.5 turns Helicotrema connects vestibuli and tympani at apex 3 compartments Scala vestibuli, media, tympani Endolymph Intracellular fluid low Na; high K Perilymph Vestibuli and tympani (extracellular) high Na; low K Footplate attached to vestibule of labyrinth Contiguous with scala vestibuli Walls of scala media Reissner’s membrane Basilar membrane – organ of Corti Lateral wall – stria vascularis Na-K ATPase Cochlear implant into scala tympani Organ of Corti Outer hair cells (3) Inner hair cells Supporting cells Tectorial membrane Inner Hair Cells Type 1 neurons many spiral ganglion cells to 1 inner hair cell Efferents project lateraly Outer Hair Cells More numerous Innervated by type 2 afferent neurons One spiral ganglion cell branches to many outer Efferents project medially Sound vibrates basilar membrane Stiffer at base than apex Tonotopically constructed with high freq maximal displacement at base Cochlear amplification Outer hair cells enhance frequency pick up Hair cells have stereocilia Directly contact tectorial membrane in outer Deflection causes K+ influx depolarization Auditory Nerve CN 8 Auditory nerve function measured by tuning curves of type I cells (inner) Sound is presented an frequency and intensity adjusted until change in firing rate Nadir is where nerve is best at that frequency Characteristic frequency SNHL loses tips Presbycusis caused by dysfunction of stria vascularis Normal two-tone suppression OAE Sound detected in EAC emanating from cochlea Spontaneous OAE Transient evoked OAE Frequency matched deficit 20-30 dB loss will lose OAE Used in newborn hearing Auditory Central Nervous System Cell bodies in spiral ganglion with afferent to hair cells, axons sent to cochlear nucleus Mostly contralateral innervation to superior olivary complex, small ipsilateral contribution Stimulation of the contralateral ear is usually stimulatory and ipsilateral is inhibitory Medial portion of superior olivary complex is where crossed efferents to outer cell originates Lateral superior olivary complex is where efferents to uncrossed inner originates Next synapse is at inferior colliculus (crossing) Medial geniculate body (crossing) Slyvian fissure of the auditory cortex in temporal lobe (no crossing) There is tonotopic orginaztion Auditory Brainstem Response 7 waves measured after given stimulus I and II: 8th nerve III : Cochlear nucleus IV: superior olive V : inferior colliculus Auditory steady-state Response Continuous tones used with