Module D-11 Flashcards
What is sound?
pressure waves generated by mechanical vibrations
what are 3 characteristics of sound?
1) Frequency - perceived as a high or low tone or pitch
2) Intensity or amplitude- perceive as loudness
3) the point of origin - location
What is unit for the frequency of sound?
cycles per second ( cps) or Hertz ( Hz)
What is frequency range of sound audible to humans?
20 to about 20,000 Hz
What is sound intensity?
sound pressure levels (p) relative to the human auditory
threshold (p0) at 1000 Hz
Equation for sound intensity
Intensity (dB) = 20 log (p/p0)
unit for sound intensity
Decibels (dB)
What is the speed sound travels through air?
331 meter per second (m/s)
Describe pathway of sound into outer ear
The outer ear, filled with air, focuses sound into the external auditory meatus. Pressure waves generated by sound pass through the external auditory meatus
and produce vibrations of the tympanic membrane.
What separates the inner and outer ear?
Tympanic membrabe
What is the middle ear filled with?
air
How is the middle ear connected with the nasopharynx?
Eustachian ( pharyngotympanic ) tube
What are the ossicles of the ear?
malleus, incus and stapes
What are the 2 muscles of the inner ear?
m. tensor tympani and the m. stapedius
What is the function of the 2 muscles of the inner ear?
Contract To prevent damage to the inner ear during high intensity sound
The stapes vibrates the _______ window to produce vibratory waves of the inner ear
Oval
What is the bony compartment that contains the inner ear?
the Cochlea
Which compartments of the inner ear contain Perilymph?
scala vestibuli and scala tympani
Which compartments of the inner ear contain Endolymph?
scala media
The hair cells are located in the ___________ of the chochlea
Organ of corti
Where are the cell bodies of the afferents that receive the signal from the hair cells?
Spiral ganglion (form axons of auditory nerve CN VIII)
What are the 2 mechanisms of sound amplification in the middle ear?
1) Size difference of Tympanic membrane compared to oval window
2) Lever Ratio of the Ossicular Chain
How does the size difference cause pressure amplification of sound?
because the smaller the surface area the greater the pressure produced for the same force
How does the lever ratio of the ossicular chain cause pressure amplification?
Large movements (with little force) of the tympanic membrane are transformed into little movements (with greater force) at the oval window
By how much does the middle ear amplify pressure?
70-100 fold
Which ossicle is the tensor tympani muscle attached to ?
Malleus
Which ossicle is the stapedius muscle attached to ?
Stapes
Which nerve innervates the tensor tympani muscle?
Trigeminal nerve V
Which nerve innervates the Stapedius muscle?
Facial nerve VII
What happens when the 2 inner ear muscles are contracted
1) tensor tympani, limits the movement of the tympanic membrane;
2) stapedius, limits the movement of the stapedius
What are the 3 fluid compartments of the cochlea?
the scala vestibuli, the scala media and the scala tympani.
Perilymph s similar in composition to ___________
Extracellular fluid
The part of the cochlear labyrinth where the scala tympani and the scala vestibuli meet
HELIOCTREMA
What causes the High K+ levels in the endolymph of scala media?
due to an active secretion process of the stria vascularis
Where is the Stria Vascularis located?
Lateral wall of the scala media
Which membrane separates the scala media from the scala tympani?
Basilar membrane
Which membrane separates the scala media from the scala vestibuli?
Reissner’s membrane
Why are travelling waves produced by sound in the inner ear and not compression waves as in air?
because fluid isn’t compressed it moves
Describe movement of sound from stapes into cochlea
Movement of the stapes produces pressure on the oval window, pushing against the perilymph compartments (and
indirectly on the endolymph compartment) in the cochlea and pulling back.
Describe signal transduction in organ of corti
travelling waves through the cochlea, which deflect the basilar membrane relative to the tectorial membrane
which then causes deflection of the stereocilia
Which cells are the signal amplifiers of the INNER ear?
Outer hair cells
Which cells are the transducers of sound?
Inner hair cells
How do Outer hair cells cause signal amplification?
motor proteins cause shortenings of the outer hair cells
when they are depolarized, and elongation when they are at rest
Part of the Cerebral cortex that is an element of the auditory pathway
Transverse Temporal gyrus
Part of the Thalamus that is an element of the auditory pathway
Medial geniculate nucleus
Part of the Midbrain that is an element of the auditory pathway
Inferior colliculus
Part of the Pons that is an element of the auditory pathway
- Lateral lemniscus nucleus
- Superior olive
- Trapezoid nucleus
Part of the medulla that is an element of the auditory pathway
Cochlear Nuclei
Part of the PNS that is an element of the auditory pathway
Auditory nerve VIII , Spiral ganglion
Where does the auditory nerve enter the brainstem?
ponto-medullary junction, and the fibers synapse in
the anterior and posterior cochlear nuclei
Which Lesions cause unilateral hearing loss?
lesions affecting the structures of the ear, the eighth nerve, or cochlear nuclei
Lesions that affect sound localization
Lesions of the inferior colliculus
Why are bilateral hearing loss more common than unilateral one?
the auditory pathways are characterized by extensive
crossing fiber connections at each level
3 ways to categorize hearing loss:
- Unilateral or bilateral
- Conductive or sensorineural
- Acquired or age related
What is Otosklerosis?
a gradual replacement of normal bone of the bony
labyrinth and the stapes footplate by lamellar new bone. This leads to a fusion of the stapes with the borders of the oval window
What type of hearing loss is Otosklerosis?
Conductive hearing loss, up to 40 dB sound pressure
What is a vestibular Schwannoma ?
- a benign tumor originating from the Schwann cells of the vestibular division of CN VIII
tumor - compresses the vestibulo-cochlear nerve within the internal auditory meatus.
What are the symptoms of a vestibular Schwannoma?
UNILATERAL sensorineural hearing loss and tinnitus
What is Meniere’s disease?
Abnormalities of endolymph circulation can lead to significant dilation of endolymph compartments and degeneration of hair cells
Symptoms of Meniere’s disease?
characterized by recurrent sudden attacks of vertigo, tinnitus and sensorineural hearing loss
What type of sounds cause hearing loss?
Extremely loud percussive sounds, such as explosions or gun fire, can rupture the tympanic membrane and cause conductive hearing loss.
Repeated exposure to less dramatic, but still high sound intensities (100dB or higher), including sounds generated by machinery or amplified music (also loud sound exposure through head phones), causes sensorineural hearing loss, due to the damage to hair cells in the organ of Corti.
what is presbycusis?
a progressive bilateral and symmetrical sensorineural hearing loss associated with aging
What gets damaged over time as we age?
hair cells, peripheral nerve
damage and damage to central auditory pathways
What needs to be intact for hearing aids to be used?
the elements of sound conduction in the
middle ear, as well as the sensorineural elements, including hair cells in the inner ear and the auditory pathways
How do cochlear implants work?
The stimulating electrodes are surgically inserted into the cochlea and on the
reception of sound, suitable patterns of electrical stimuli are delivered to the
fibers of the cochlear nerve.
used for sensorineural hearing loss where only hair cells are damaged but afferent fibers are intact
