The Process of Hearing 1. Sound is caused by vibrations/waves moving through a medium

Sound waves Volume= determined by amplitude (height) of wave Pitch= determined by frequency (# of waves per unit time)

Pathway of sound waves 1.Pinna directs sound waves through auditory canal 2.Sound waves first hit tympanic membrane (ear drum) 3.Vibrations move through malleus, incus, and stapes, then through oval window to perilymph 4.Fluid conduction through cochlea moves basilar membrane

Pathway of sound waves (cont’d) 5. Sensory hair cells on Organ of Corti are stimulated when stretched 6. Hair cells fire and transmit nerve impulses along cochlear nerve

Different frequencies travel different distances in fluid  stimulate different hairs Lower frequencies travel farther into cochlea, stimulating different part of basilar membrane Different hairs respond to different frequencies

Higher frequencies (high pitch) stimulate hair cells nearer the stapes Lower frequencies stimulate hair cells nearer the distal end of cochlea (apex)

Higher amplitude of wave causes more movement of basilar membrane (bigger bulge) Higher the bulge causes cilia on hairs to bend more This causes increased volume Bulge on basilar membrane

Loudness (volume) detected= louder  more stretched hairs Too loud  hairs detach from membrane

Cochlear Implants When hairs are damaged but cochlear nerve remains healthy, cochlear implant can improve hearing Receiver sends code down electrode to the cochlea Wires stimulate nerve endings directly, avoiding use of hair cells