1. ANATOMY AND PHYSIOLOGY OF THE EAR

2. Main Components of the Hearing Mechanism
Outer Ear
Middle Ear
Inner Ear
Central Auditory Nervous System

3. Structures of the Outer Ear
Auricle (Pinna)
Collects sound
Helps in sound localization
Most efficient in directing high frequency sounds to the eardrum

4. External Auditory Canal
Approximately 1¼ inch in length
“S” shaped
Lined with cerumen glands
Outer 1/3rd cartilage; inner 2/3rds mastoid bone
Increases sound pressure at the tympanic membrane by as much as 5-6 dB (due to acoustic resonance)

5. Mastoid Process Bony ridge behind the auricle
Provides support to the external ear and posterior wall of the middle ear cavity

6. Tympanic Membrane Thin membrane
Forms boundary between outer and middle ear
Vibrates in response to sound
Changes acoustical energy into mechanical energy

7. The Ossicular Chain A: Malleus B: Incus C: Stapes
Ossicles are smallest bones in the body
Act as a lever system
Footplate of stapes enters oval window of the cochlea

8. Eustachian Tube
Lined with mucous membrane; connects middle ear to back of the throat (nasopharynx)
Equalizes air pressure
Normally closed except during yawning or swallowing
Not a part of the hearing process

9. Stapedius Muscle Connects the stapes to the middle ear wall
Contracts in response to loud sounds; known as the Acoustic Reflex

10. Structures of the Inner Ear
Cochlea - Snail-shaped organ with a series of fluid-filled tunnels; converts mechanical energy into electrical energy

11. Structures of the Inner Ear (Cont.)
Oval Window – located at the footplate
of the stapes; when the footplate vibrates,
the cochlear fluid is set into motion
Round Window – functions as the pressure relief port for the fluid set into motion initially by the movement of the stapes in the oval window

12. Organ of Corti
The end organ of hearing; contains stereocilia and hair cells.

13. Hair Cells Frequency-specific
High pitch sounds = base of cochlea
Low pitch sounds = apex of cochlea
When the basilar membrane moves, a shearing action between the tectorial membrane and the organ of Corti causes hair cells to bend

14. Vestibular System Consists of three semi-circular canals
Shares fluid with the cochlea
Controls balance
No part in hearing process

15. Central Auditory System
8th Cranial Nerve or “Auditory Nerve” carries signals from cochlea to brain
Fibers of the auditory nerve are present in the hair cells of the inner ear
Auditory Cortex: Temporal lobe of the brain where sound is perceived and analyzed

16. How Sound Travels Through The Ear...
Acoustic energy, in the form of sound waves, is channeled into the ear canal by the pinna. Sound waves strike the tympanic membrane, causing it to vibrate like a drum, and changing it into mechanical energy. The malleus, which is attached to the tympanic membrane, starts the ossicles into motion. (The middle ear components mechanically amplify sound). The stapes moves in and out of the oval window of the cochlea creating a fluid motion. The fluid movement within the cochlea causes membranes in the Organ of Corti to shear against the hair cells. This creates an electrical signal which is sent via the Auditory Nerve to the brain, where sound is interpreted!

17. QUESTIONS?