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.

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

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

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

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

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

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

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)

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

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

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

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

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

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

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!