1. The Ear and Hearing

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

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

4. Incus Malleus Stapes Fig10.07
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Incus
Malleus
Stapes
© The McGraw-Hill Companies, Inc./Jim Womack, photographer

5. 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. 3a. Oval window -receives amplified sounds waves from stapes. 3b. Round window-opening to inner ear, moves opposite oval window to ensure fluid moves in cochlea. 3c. Cochlea-hearing, hair cells detect frequency of sound 3d. Cochlear nerve -sends information about sound to brain 3e. Vestibular nerve -sends information about the heads position to brain 3f. Vestibule-detects static equilibrium (the position of the head when still) 3g. Semicircular canals -detect dynamic equilibrium (motion of head) and aids in balance

6. Fig10.08 Osseous labyrinth Perilymph Membranous labyrinth Endolymph
Copyright © The McGraw-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
window
Maculae
Cochlea

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

11. 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.

12. 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 membrane-
closer 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.

13. 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.

14. 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.

15. Hearing Loss Limits

16. iPOD Listening Times

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