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What are the 2 primary components of the outer ear?
- depression area of the auricle (pinna)
- serves to collect and direct sound to the external auditory meatus (opening to ear canal)
What structures of the outer ear are responsible for resonance?
What divides the outer and middle ears?
tympanic membrane (ear drum)
- connects nasopharynx to the middle ear
- usually closed except when yawning or swallowing
- allows fluid to drain from the middle ear
- allows us to equalize pressure in the middle ear (ears pop when going up in a plane or up the mountain)
- in cochlea
- filled with perilymph fluid
- connects scala tympani and scala vestibuli
- between scala tympani and scala vestibuli
- filled with endolymph fluid
Orgain of corti
- sensory organ of hearing
- in the scala media
What structure contains several thousand receptor hair cells?
organ of corti which rests on the basilar membrane in the cochlea (inner ear)
Order of the ossicles
- malleus (hammer)
- incus (anvil)
- stapes (stirrup)
What are the various functions served by the outer ear?
- to distinguish the elevation of sound
- to distinguish whether the sound is in front
- protects delicate middle ear from foreign bodies
- concha enhances the frequencies at 5000 Hz (resonant frequency of this space) and the external auditory canal enhances the frequencies at 2500 Hz (resonant frequency of this space)
What kinds of frequencies are amplified by the outer ear?
- high frequencies
- enhanced high frequency sounds aid in understanding conversational speech (consonant sounds are high frequency sounds)
What is the resonant frequency of the ear canal for an adult?
approx. 2500 Hz
What is the resonant frequency of the concha of an adult?
approx. 5000 Hz
Where do the sound vibrations travel after striking the eardrum?
through the ossicles to the footplate of the stapes that rests in the oval window, then to the inner ear
What compensates for loss of sound energy when going from air to a fluid filled medium through what two primary mechanisms?
- the middle ear
- 1. the areal ratio of the tympanic membrane to the footplate of the stapes
- 2. a complex level system existing within the ossicles
What do the vibrations cause when the ear is stimulated by sound?
the oval window to move in, at the same time that the round window is moving out
What do fluid vibrations through the inner ear do?
push the round window out when the oval window is pushed in by the rocking of the stapes footplate
How are the nerve cells in the cochlea arranged?
What kind of nerve fibers does the base of the cochlea contain?
- high frequency
- tonotopic organization
What kind of nerve fibers does the apex of the cochlea contain?
- low frequency
- tonotopic organization
How is the auditory nerve organized?
- so that each characteristic frequency corresponds to a place within the nerve bundle
- tonotopic organization
For frequencies between 50 and 5000 Hz, what may underlie the perceived pitch?
both place-based and timing-based codes for sound frequency
What is the transducer function (transduction function)?
it is the shearing forces applied to the cilia in the organ of corti in response to acoustic stimulation which gives rise to electrical potentials (receptor potentials)
What are OAEs?
otoacoustic emissions or cochlea echoes
What type of OAEs were first measured in humans?
TEOAEs or transient evoked otoacoustic emissions (first measured by david kemp)
What is the response of the action potentials evoked by the auditory nerve fibers?
- "all or none"
- the amplitude of the response does not vary
- once it is evoked there is always a 100% response
What is the characteristic frequency of a nerve fiber?
the frequency requiring the least amount of stimulus intensity to provoke a response from the nerve fiber
Afferent pathways of the auditory CNS
What is the ratio of nerve fibers in the afferent pathways to the nerve fibers in the efferent pathways?
100 to 2
What are the characteristics of the auditory brainstem response (ABR)?
- it can be recorded reliably and easily
- it can be used to estimate hearing loss
- it is useful in assisting with detection of neurological problems along the path of the auditory CNS
What is the hearing threshold?
the lowest level at which the sound can be detected 50% of the time
What are a normal hearing person's best (lowest) thresholds?
2000 to 4000 Hz
What is the range of audibility for the normal hearing human ear?
What is masking?
refers to the ability of one acoustic signal to obscure the presence of another signal so it cannot be detected
What is binaural processing?
- allows us to combine or integrate the neural information from both ears
- one of the key functions of the auditory CNS
What is binaural processing necessary for?
localization of sound and the ability to hear in noisy situations
What may genetic transmission of hearing loss be due to?
- autosomal (non-sex linked) dominant inheritance
- autosomal recessive inheritance
- sex linked inheritance (x-linked)
What percentage of all auditory disorders do hereditary factors make up?
a trait or disorder that arises from the individual's genes
a trait or disorder that is not attributable to genetic causes
a trait or disorder that is present at birth
Are congenital hearing losses hereditary?
- they may or may not be
- ex. maternal rubella causes hearing loss that is present at birth
Can hearing loss be hereditary but not congenital?
- ex. hereditary types of hearing loss that don't manifest until adulthood
What are causes of outer ear disorders?
- deformity of the pinna
- collapsed canals
- cerumen or foreign bodies
- external otitis
- cysts and tumors
What is the common cause of hearing loss for people in their 20's, 30's and 40's?
What is otosclerosis caused by?
a buildup of spongy bone that immobilizes the stapes footplate
What can otosclerosis be treated with?
- surgery (stapedectomy)
- hearing aid
What are medical complications associated with otitis media?
- cholesteotoma (growth of skin and debris associated with perforation of eardrum)
- facial paralysis (facial nerve crosses through the middle ear)
- perforation of the tympanic membrane (hole in the eardrum)
- tympanosclerosis (plaque that forms on eardrum and ossicles causing stiffening)
- adhesive otitis media (glue ear)
What is the prevalence of otitis media?
- 76-95% of children will have at least one episode by the age of 6 yearsone of the most common diseases of childhood
- prevalence is highest in the first 2 years of life
- more common in males
- occurs more often in winter and spring
What are procedures used to alleviate otitis media?
- surgery (myringotomy and adenoidectomy)
What are risk factors for hearing loss among newborns?
- in utero infections (storch- syphillis, toxoplasmosis, rubella, cytomegalovirus, herpes simplex)
- low birthweight
- family history of hearing loss
- evidence of a sydrome
- craniofacial abnormalities
What is a common cause for unilateral hearing loss that occurs after birth (post-natally)? Bilateral?
- refers to damage to the nerve fibers along the ascending auditory pathways from the internal auditory meatus to the cortex
- most often due to a tumor (other causes include MS and CVA)
- hearing loss associated with aging
- sloping, high frequency, sensorineural hearing loss
- progression is usually more pronounced in men than in women
Noise induced hearing loss (NIHL)
- characterized by:
- 1. an audiogram with a "4 K notch" configuration
- 2. a permanent sensorineural hearing loss in the high frequencies and near normal hearing in the low frequencies
- 3. destruction of outer hair cells in the cochlea in the base with little or no inner ear damage near the apex
usually cause high frequency hearing loss
Why should a speech pathologist know about the complications of otitis media?
it's the most common cause of hearing loss in children and it could be the cause of their speech problems
Why is binaural hearing important?
it helps you localize sound and allows you to focus on one specific sound and block out background noise
Which type of hearing loss can usually be treated medically? Conductive or sensorineural?