sound vibration and motion sickness Flashcards
impulses are sent from inner ear to brain via
auditory nerve
acoustic reflex
The acoustic reflex is a response of the middle ear to sound.
Sound is collected in the outer ear, amplified and transmitted to inner ear. The mechanical energy is converted into electrical energy as it stimulates the auditory nerve. The electrical impulse travels through the auditory tracks of the brainstem which involves the cochlear nucleus and the superior olivary complex.
There is crossing of the nerve tracts at the cochlear nucleus so that sound perceived by one ear will be sent bilaterally to the auditory cortical areas. The acoustic reflex is generated at the level of the superior olivary complex.
When a loud stimulus is presented (70 dBA or above) this complex is stimulated and in turn it sends bilateral electrical impulses via the cranial nerve VII to the stapedius muscles of the middle ears causing a measurable change in the tension of the ear drum.
The acoustic reflex tells us that the brain’s “wiring” is intact and working.
auditory nerves go to…..
what happens there?
right and left cochlear nucleus
nerve tracts cross so info is sent bilaterally to the auditory cortical areas/right and left superior olivary complexes
a loud sound will cause what after the olivary nucleus?
bilateral impulses sent back to stapedius muscle via facial nerve -> changes tension in ear drum
decibel scale
logarithmic, cant be just added
–> for two identical sounds, just add 3 dB
–> for three, add 5 dB
dB of hazardous cont/intermittent noise?
discomfort threshold?
hazardous impact/impulse noise?
tissue damage?
death?
85
120
140
170
180+
ex: one machine is 90dB
two identical machines?
93 dB
STS
standard threshold shift
a change in hearing from baseline when on the audiogram:
sum of the shift at 2000, 3000, and 4000 hz is greater or equal to +30dB
how to verify STS?
•Repeat the test twice within the next 30 days; one within 14 hrs of rest from noise
audiogram
traces the sensitivity of sound reception
three types of audiograms
normal
high freq loss
conductive loss
normal audiogram
range between -10 to 25 dB
high freq loss audiogram
Losses at 2000 Hz and above are classified as high frequency sensorineural hearing losses. The classic curve is the notched loss. This “notch,” which will be shown on a subsequent slide, most frequently occurs at 4000 Hz
damage to the inner ear and/or the pathway to the brain. It is commonly seen in noise-induced hearing loss, presbycusis (age-related hearing loss) and acoustic trauma
conductive hearing loss audiogram
•conductive hearing loss in both ears. Note that the bone conduction (brackets) is better than air conduction.
The gap between bone and air conduction must be greater than 10 dB to be labeled as a a conductive hearing loss.
diseases involving the middle ear such as Eustachian Tube Dysfunction, Otitis Media and Otosclerosis
- Type “A” = Normal Middle Ear Status
- Normal Middle Ear Pressure -150 - +100 daPa
- Type “Ad” = Hypermobile Middle Ear
- Possible ossicular discontinuity or monomeric TM
- abnormally excessive (or floppy) movement in response to pressure
- Type “As” = Stiff Middle Ear system
- Stiff, scarred TM
- “stiffening” pathologies such as otosclerosis or tympanosclerosis.
- Type B = Flattened = Immobile Middle Ear
- Fluid behind the TM
- perforated ear drum, cerumen impaction, or a PE tube, although, it is also completely flat when the measuring device is pressed against the ear canal wall.
•Type “C” = Eustachian Tube Dysfunction
•Negative pressure behind the TM
•a negative pressure in the middle ear. Most commonly this means eustachian tube dysfunction
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