Fundamentals Audiology, of Sound, Anatomy & Physiology of Hearing Mechanism
Chapter 14
Overview
What is audiology? Fundamentals of sound
Frequency, pitch, pure tone, complex tone, periodic, aperiodic, amplitude loudness, dB
Auditory A & P
Outer ear Middle ear Inner ear Physiology of hearing
What is Audiology?
The discipline involved in:
Prevention, identification, and evaluation of hearing disorders
Prevention: e.g., public awareness re: noise induced hearing loss
Selection of hearing aids Habilitation/rehabilitation of hearing loss
Habilitation: For those born with a hearing loss Rehabilitation: For those w/ acquired hearing loss
An audiologist:
Expert in hearing and hearing disorders
Audiologists work in:
private practice settings Hospitals rehabilitation centers Schools
Classroom acoustics a big focus right now Kids don't have processing ability to screen out extraneous noise the way adults do
hearing aid companies Industry
E.g., hearing conservation programs ( such as coal mines)
Fundamentals of Sound
Sound
Vibrations traveling through a medium (such as air or water) that are audible Sound is caused by Vibrations Sound waves occur even if there is no one present to hear them
Frequency
Physical characteristic Number of vibrations per second Measured in Hertz (Hz.): Cycles per second E.g., Middle "C" on the piano = 256 Hz ~500-4000 Hz = speech frequency range
Pitch
Perceptual characteristic Perceptual correlate of frequency
That is, you can't hear frequency, but you can hear pitch
When the frequency changes, we hear different pitches
Increase frequency Increase in pitch
Pure tone
Tone of a single frequency e.g., a tuning fork
Complex tone
A tone containing two or more different frequencies Most sounds are complex tones E.g., sound of vehicle on the street, sound of construction outside
Periodic
A pattern that repeats itself at regular intervals E.g.
Dial tone on a phone
Aperiodic
No repetitive pattern E.g.
the static between stations on the radio (white noise) The "s" sound
Amplitude/intensity
Extent molecules are displaced during vibration Molecules do not move from point A to point B, remain in place and swing back and forth (think of ripples in a puddle or "the wave" during a sporting event)
Loudness
Perceptual correlate of amplitude The physical characteristic of intensity determines the psychological sensation of loudness Loudness is a perceptual event
That is, you can't hear amplitude, but you can hear loudness
Higher intensity the greater the loudness Loudness is measured in decibels
Decibel (dB)
A measure of sound intensity Helps compare the intensity of one sound against another the higher the dB, the louder the sound
Intensity of normal conversational speech varies between 50 and 70 db Live rock concerts 95 - 110
Overview
What is audiology? Fundamentals of sound
Frequency, pitch, pure tone, complex tone, periodic, aperiodic, amplitude loudness, dB
Auditory A & P
Outer ear Middle ear Inner ear Physiology of hearing
Auditory Anatomy and Physiology
Three main divisions of ear
Outer ear Middle ear Inner ear We'll start with the outermost part of the outer ear, and work our way in Notice on diagram:
Pinna, ear canal, tympanic membrane, eustatian ossicles, tube, cochlea
The Outer Ear
Pinna
Funnels sound into ear canal Helps localize sound
Ear canal
Increases the intensity of sound waves by concentrating them in a smaller area Cerumen (wax) helps to keep the ear canal clean
Smells bad to keep the bugs out!
The Middle Ear
Tympanic membrane (Eardrum) Middle ear space Eustachian tube Ossicles
The Middle Ear
Malleus
Incus
Tympanic Membrane
Stapes
Tympanic Membrane
Cone shaped structure of tissue Concentrates sound at its center Sound waves hit the tympanic membrane causing it to vibrate
Middle Ear Space
Lined with a mucous membrane Filled with air Connected to Eustachian tube
Eustachian Tube
Connects the M.E. to the nasopharynx Equalize pressure
When negative pressure builds up, it pulls the tympanic membrane into the middle ear space; Ears "pop:" this is your Eustachian tube opening and closing to release the pressure
Passageway for air to move in and out of middle ear Can be opened by yawning and swallowing (this lets fresh air into the middle ear)
Ossicles
Three small bones of the middle ear
The 3 smallest bones in the body
As a group, these 3 bones are called the "ossicles"
Malleus (Hammer) Incus (Anvil) Stapes (Stirrup)
Connect ear drum to inner ear Amplify vibration of ear drum
Ossicles
The Inner Ear
Semicircular canals Cochlea Acoustic nerve (cranial nerve VIII)
Inner Ear
Semicircular Canals
Oval window
Cochlea
Semicircular Canals
Part of the vestibular system Help maintain balance Filled with fluid On 3 different planes (1 = vertical, 1 horizontal in 1 direction, 1 horizontal in the other)
This is what gives you information when your head is turning
Cochlea
Primary inner ear structure of hearing Mechanical impulses from the ME are converted into electrical impulses Snail shaped Filled with fluid High frequency sounds stimulate base Low frequency sound stimulate tip Vibration stimulates the hair cells
Cochlea
Acoustic Nerve (VIII)
Carries electrical impulses from cochlea to the brain
Primary auditory area in the Temporal lobe
Review
pinna, ear canal, tympanic membrane, ossicles, eustachian tube, cochlea
Physiology of Hearing
Sound waves are directed by the pinna into the ear canal Waves strike the eardrum & cause it to vibrate The eardrum is connected to the malleus, which moves the ossicles back and forth
This is the mechanical part of the process
The movement of the footplate of the stapes makes makes wave in the fluid of the cochlea
This is the sensory part of the process
Pressure of the waves causes vibrations in the cochlea stimulating the hair cells
The movement of the hair cells generates nerve impulses that are electrical The nerve impulses are passed on to the 8th nerve and transmitted to the auditory area of the brain
Air and bone conduction
Air conduction
Sound waves travel through the air to the outer ear (starting at the pinna) and are transmitted through the
Bone conduction
Vibrations of bone cause cause movement of fluids in the inner ear The larger bones of the skull conduct sound because they vibrate in response to sound waves We normally hear our own voice through a combination of air and bone conduction
Audiologists test both air and bone conduction during hearing evaluations