ANATOMY AND PHYSIOLOGY OF THE EAR (HEARING)
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
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
Tympanic Membrane: Thin membrane Forms boundary between outer and middle ear Vibrates in response to sound
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 &Organ Of Corti 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.
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!
Vestibular System Consists of three semi-circular canals Shares fluid with the cochlea Controls balance