1. Journal#5: What would happen if you were born without cones
Journal#5: What would happen if you were born without cones? Had a vitamin A deficiency? Had a blocked canal of Schlemm?
Objective #4: Describe the structures of the outer, middle, and inner ear and explain how they function in hearing and equilibrium. Trace the pathways to the brain.

2. ANATOMY AND PHYSIOLOGY OF THE EAR Interactive pgs. 573-586

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

4. Structures of the Outer Ear
Auricle (Pinna)
Collects sound
Localization
Amplifies sound (approx. 5-6 dB)

5. External Auditory Canal:
Approx. 1 inch in length
“S” shaped
Lined with cerumen glands
Outer 1/3 surrounded by cartilage
Inner 2/3’s surrounded by mastoid bone

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

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

8. The Ossicles: A: Malleus B: Incus C: Stapes Stapedius Muscle
Smallest bones in the body
Acts as a lever system
Footplate of stapes enters oval window of the cochlea
Stapedius Muscle
Connects stapes to wall of middle ear
Contracts in response to loud sounds (called the Acoustic Reflex)

9. Eustachian Tube (AKA: “The Equalizer”)
Lined with mucous membrane
Connects middle ear to nasopharynx
“Equalizes” air pressure

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

11. Organ Of Corti: The end organ of hearing
Contains stereocilia and hair cells.

12. Hair Cells: Frequency specific High pitches= base of cochlea
Low pitches= apex of cochlea

13. Vestibular System Consists of three semi-circular canals
Shares fluid with the cochlea
Controls balance

14. Central Auditory System
VIIIth Cranial nerve or “Auditory Nerve”
Carries signals from cochlea to brain
Auditory Cortex
Temporal lobe of the brain where sound is perceived and analyzed

15. How Sound Travels Through The Ear...
1. Acoustic energy, in the form of sound waves, is channeled into the ear canal by the pinna
2. Sound waves hit the tympanic membrane and cause it to vibrate, like a drum, changing it into mechanical energy
3. The malleus, which is attached to the tympanic membrane, starts the ossicles into motion
4. The stapes moves in and out of the oval window of the cochlea creating a fluid motion
5. The fluid movement causes membranes in the Organ of Corti to shear against the hair cells
6. This creates an electrical signal which is sent up the Auditory Nerve to the brain
The brain interprets it as sound!