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