EAR AND HEARING Resonant Frequencies of pinna and EAM are
1500-8000 Hz
Tympanic Membrane 3 tissue layers outer: epithelial intermediate: fibrous
inner: mucous
Portions of the Ossicles
Anterior Crus (Crus Anterius) Base (footplate)
Structures of the Middle Ear
Ossicles
Middle Ear Mechanism
Impedance (resistance to flow of energy) matching device Increases pressure of signal arriving at cochlea 25dB gain between TM and OW due to area ratio
lever advantage of ossicles provides a 2dB gain
Inner Ear
Semi Circular Canals
Cochlea:
Tonotopic
Arrangement -Low frequency processed at apex, high at apex
-Modiolus
Organ of Corti
Traveling wave
Shearing Force
Traveling Wave
• Initiation caused by compression of the fluid in the scala vestibuli which is transmitted directly to the basilar membrane
• Point of maximum excursion of BM determines fx information transmitted to brain
• BM quickly damps after reaching maximum excursion
• Fx analysis of BM determined by stiffness, thickness and width of membrane– Stiffer, thinner, narrow at base
Outer and Inner
Cells Of Organ of
Corti
Many nerve cells innervate each inner hair cell, excitation from fluid flow and turbulence of endolymph
Many outer hair cells are innervated by one nerve fiber, excitation from shearing effect on cilia
VIII Cranial Nerve: Vestibular and Cochlear CN: tonotopic representation in tuning curves SOC: localization of sound in space IC: inhibition response, time and intensity sensitivity MGB: relay to the cortex HG: full tonotopic map CC: receives stimuli from contralateral ear via ipsilateral MGB