The Ear and Hearing 1 Outer Ear main

The Ear and Hearing

1. Outer Ear- main purpose is to funnel sound waves to inner ear. 1 a. Auricle-gathers sound waves 1 b. External acoustic meatus- transmits sound waves to tympanic membrane 1 c. Tympanic membrane (eardrum)-amplifies sound and transmits it to middle ear.

2. Middle Ear (tympanic cavity)- main purpose is to transmit sound waves through movement and vibration of the ossicles (bones) to the inner ear. 2 a. Malleus-receives sound waves from eardrum 2 b. Incus-transmits sound waves to stapes 2 c. Stapes-transmits sound waves to oval window 2 d. Auditory tube (Eustachian tube)-connects middle ear to throat and helps maintain air pressure 2 e. Tympanic cavity- air filled cavity that connects to the auditory tube

Fig 10. 07 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Incus Malleus Stapes © The Mc. Graw-Hill Companies, Inc. /Jim Womack, photographer 4

3. Inner Ear- major purpose is to generate movement of tiny hair like cells with a fluid called endolymph and perilymph to transmit impulses to the brain through nerves. 3 a. Oval window -receives amplified sounds waves from stapes. 3 b. Round window-opening to inner ear, moves opposite oval window to ensure fluid moves in cochlea. 3 c. Cochlea-hearing, hair cells detect frequency of sound 3 d. Cochlear nerve -sends information about sound to brain 3 e. Vestibular nerve -sends information about the heads position to brain 3 f. Vestibule-detects static equilibrium (the position of the head when still) 3 g. Semicircular canals -detect dynamic equilibrium (motion of head) and aids in balance

Fig 10. 08 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Osseous labyrinth Perilymph Membranous labyrinth Endolymph Osseous labyrinth (contains perilymph) Membranous labyrinth (contains endolymph) Semicircular canals Utricle Vestibular nerve Saccule Cochlear nerve Scala chambers (cut) containing perilymph Cochlear duct (cut) containing endolymph Ampullae Oval window Round Maculae window Cochlea 6

Video Links How Hearing Works Conductive Hearing Loss Sensorineural Hearing Loss Cochlear Implants

I. HOW WE HEAR A. The outer ear- funnels sound waves of a given frequency (measured in hertz) and intensity (measured in decibels) to the tympanic membrane, causing it to vibrate. B. Vibration of the tympanic membrane causes vibrations in the middle ear ossicles(tiny bones)malleus, incus and stapes, which vibrates the oval window of the cochlea. C. Vibration of the oval window sets up a traveling wave of perilymph in the vestibule of the inner ear. The wave passes through the cochlear duct- filled with endolymph.

D. The sensory structure of the cochlea is called the organ of Corti. 1. Organ of Corti- consists of sensory hair cells on the basilar membrane. The hair cells send messages to vestibulocochlear nerve when stimulated. 2. High frequency sounds- cause maximal displacement of the basilar membranecloser to its base near the stapes. 3. Low frequency sounds- produce maximal displacement of the basilar membrane closer to its apex. 4. Pitch discrimination -- depends on the region of the basilar membrane that vibrates maximally to sounds of different frequency.

Hearing Loss Conductive hearing loss -something is inhibiting the sound waves from reaching the inner ear Malformation of outer ear, ear canal, or middle ear structures. Fluid in the middle ear from colds. Ear infection. Allergies. Poor Eustachian tube function. Perforated eardrum.

Hearing Loss Sensorineural hearing loss -indicates the malfunction of the inner ear in conducting the message to the brain. Exposure to loud noise. Head trauma. Virus or disease. Autoimmune inner ear disease. Hearing loss that runs in the family. Aging (presbycusis) Malformation of the inner ear. Meniere's Disease.

Hearing Loss Limits

i. POD Listening Times

Exposures >85 d. B for more than 10 minutes at a time may cause hearing loss