Hearing and the Ear Flashcards
Hearing
• The hearing mechanism takes the acoustic wave
converts it into mechanical motion, then converts it
to a hydraulic wave, which triggers a bio-electrical
signal.
• The brain takes the bio-electrical signal and decodes
• cognitive information (knowledge, ideas,
judgment)
• affective information (emotion, feeling, mood)
Ear Parts
• The ear is divided into three parts
•Outer
•Middle
•Inner
Outer
• The outer ear includes
• Pinna
•Auditory canal
(external ear canal)
The Pinna
• The job of the Pinna is to catch and focus the
acoustic waves into the ear canal
•Note that the folds in the pinna cause path length
differences (phase shifts). The comb filter results of
these phase shifts are used by the brain to help in
sound source location of high frequencies
The Pinna directs the sound into the ear canal.
The Pinna helps locate sound from above.
Auditory Canal
• The auditory canal is 1 to 1.5 inches long
• Like any pipe it has a resonant frequency
• The resonant frequency is around 3 k Hz
•We hear best at this frequency
Middle Ear
• The middle ear includes
• Eardrum
•Ossicles
• Hammer (malleus)
• Anvil (incus)
• Stirrup (stapes)
• Eustachian tube
Ear Drum
• The ear drum vibrates as acoustic waves strike it
• The vibrations can be as small as 1/10th the
diameter of a hydrogen atom.
Ossicles
• The vibrations of the eardrum are carried across the
middle ear by three bones called the Ossicles
• The three bones are called the hammer (malleus),
anvil (incus), and stirrup (stapes)
• These bones act as a mechanical amplifier
• The amplitude of the vibrations is increased by a
factor of about 30
Acoustic Reflex
• The ear drum and the stirrup have muscles which
when tightened can reduce the amplitude to the
vibrations carried across the middle ear
• This occurs in response to loud sounds and is called
the acoustic reflex
• This results in a temporary threshold shift
Eustachian Tube
• The middle ear is an air filled chamber
connected to the outside by the Eustachian
tube, which runs to the back of the mouth
• The air pressure between the outside and the
middle ear is equalized by way of the this tube
• When this tube is closed because of a cold or
other problem there can be a difference in air
pressure between the inside and the outside of
the ear drum
• This can interfere with hearing and can result
in damage to the eardrum in extreme cases
Inner Ear
The inner ear includes
• Cochlea
•Oval Window
•Basilar membrane
•Hair cells
•Organ of Corti
•Round Window
• Semicircular canals
Cochlea
• The inner ear starts where the stirrup rests on
the oval window
• The oval window is a membrane and part of
the cochlea
• The cochlea is fluid filled
• The movement of the stirrup on the oval
window cause a wave in the fluid
• The hydraulic wave passes along the basilar
membrane
Organ of Corti
• The basilar membrane has hairs (cilia) along its
length
•Under the cilia are bundles of nerves, the Organ of
Corti
•As the hair cells are moved by the hydraulic wave
they cause the nerve endings to fire
Auditory Nerve
• The nerve firings in the Organ of Corti carries both
amplitude and frequency information to the
auditory nerve.
Noise Induced Hearing Loss
Very loud sounds can damage and destroy the hair cells. Once
destroyed they do not grow back
