Term
| what is the transmission of mechanical sound energy? |
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Definition
| auricle (pinna) -> external acoustic meatus -> tympanic membrane -> malleus -> incus -> stapes -> oval window -> fluid w/in bony labyrinth -> basilar membrane beneath the organ of corti |
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Term
| what characterizes the bony labyrinth of the inner ear? |
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Definition
| it is filled w/perilymph (CSF), low K+/high Na+ (extracellular fluid composition), and is continuous w/the subarachnoid space. |
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Term
| what characterizes the membranous labyrinth of the inner ear? |
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Definition
| this is a closed system (diffusion barrier of tight junctions) w/in the bony labyrinth which is filled w/endolymph: high K+, low Na+ (intracellular fluid composition) |
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Term
| what characterizes endolymph circulation? |
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Definition
| endolymph is secreted from the stria vascularis of the spiral ligament (part of cochlea) and travels through cochlear ducts into the saccule and endolymphatic duct (part of vestibular system) where it then communicates w/the rest of the vestibular system (utricle/semicircular ducts). it is eventually reabsorbed from the endolymphatic sac. |
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Term
| what is the structure of the cochlea? |
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Definition
| the structure spirals and becomes more narrow as it goes. the center of the shaft is called the (spongy) modiolus, which houses the spiral ganglion (primary auditory afferents which innervate the auditory receptors - hair cells). a cross section inside the hollow portion of the cochlea (bony labyrinth - perilymph) would include an extension of the modiolus called the osseous spiral lamina which reaches out about halfway until the membranous labyrinth (endolymph) is formed. the roof of the membranous labyrinth is called the vestibular membrane/reissinger’s membrane, the floor is called the basilar membrane, and the top of the spiral organ of corti inside is called the tectorial membrane. |
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Term
| what characterizes the 3 chambers of the cochlea? |
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Definition
| the scala vestibuli is on top and is where sound is transmitted into first (tympanum->malleus->incus->stapes->oval window-> scala vestibuli). vibrations travel all the way down to the helicotrema (opening which allows communication of perilymph between the scalas vestibule and tympani) and come back through the scala tympani, which is below the intermediate scala media. |
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Term
| what is the effect of sound pushing in the tympanic membrane? how do different frequencies affect this? |
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Definition
| the scala vestibuli compresses the basilar membrane (floor of the basilar membrane) down. once the vibration stops (rarefaction), the tympanic membrane pulls back, bringing some perilymph back w/it - pulling the basilar membrane upwards. different frequencies thus cause different kinds of vibration of the basilar membrane (moving back and forth due to compression/rarefaction), low frequency causes vibration furthest away from the oval membrane and high frequency causes vibration closest to the oval window. (complex sound causes many vibrations occurring at the same time). |
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Term
| what is tonotopic organization? what does this allow in terms of tx? |
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Definition
| the basilar membrane is organized tonotopically - meaning each segment has a frequency of greatest sensitivity. essentially the 4 main tonotopic areas move from closest to the oval window (high frequency) to farthest away (low frequency). this allows for the possibility of cochlear implants which in response to sound, tonotopically stimulates the auditory nerve. |
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Term
| how does the tonotopic organization of the basilar membrane project to the primary auditory cortex? |
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Definition
| in the same sequence, the auditory cortex (transverse temporal gyrus) is organized by high frequencies being most medial and low frequencies being most lateral. |
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Term
| what are the types of hearing loss up to the oval window? after the oval window? |
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Definition
| before: canal obstruction, otitis, tympanic perforation, and ossicular sclerosis. after: receptor and neural level. |
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Term
| what is the structure of the organ of corti? how does it work? |
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Definition
| the inner hair cells (type I) are closer to the center of the cochlea and the outer hair cells (type II) are farther out. the hair cells project stereocilia into the tectorial membrane and if the modiolus is on the L, movement of the tectorial membrane upward will pull the stereocilia to the R and if the tectorial membrane goes downward, the stereocilia will be pulled to the L. this is how the movement of the basilar membrane is transformed into nerve signals. supporting cells: pillar and phalangeal. |
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Term
| how does the mechano-electrical transduction of the stereocilia work? |
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Definition
| the stereocilia are connected at the top through tip links, so if the stereocilia move in respect to each other, K+ channels open. the K+ diffuses down to the cell body and changes the electric potential (causes influx of Ca+), causing release of glutamate - increasing the firing rate of the cochlear nerve. deflecting the hair bundle in the opposite direction decreases the tip link tension, closes the channels and causes less NT to be released. thus, a leak altering the electrochemical gradient of the hair cell will affect its ability to be depolarized by the vibrations of the stereocilia (affect both the auditory and vestibular systems). |
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Term
| do the stereocilia bundles have a preferred orientation? |
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Definition
| yes, and if you turn them by 90 degrees - there will not be as much of a response |
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Term
| what is the logarithmic relationship between the threshold of hearing (0 db) and the threshold of pain (140 db)? |
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Definition
| 10,000,000x the sound energy |
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Term
| what level of sound is required for permanent hearing loss in mammals? how does this occur? |
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Definition
| prolonged exposure to 90+ db which causes physical break down of the stereocilia |
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Term
| what is purpose of the efferent/afferent innervation of the hair cells? |
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Definition
| the inner hair cells (type I) make up 90% of the CN8 afferents. the outer hair cells (type II) contain more efferents which controls contraction of the outer hair cells - allows movement of the tectorial membrane and the ability to vibrate in sympathy w/the incoming vibration (tuning mechanism to distinguish between tones which are close to each other) |
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Term
| what is the CN VII innervation affecting the auditory pathway? |
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Definition
| that going to the stapedius muscle (attached to the neck of the stapes) modulates transmission of *low frequencies and is stimulated in response to loud noise. |
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Term
| what is the CN V innervation affecting the auditory pathway? |
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Definition
| that going to the tensor tympani muscle, which is attached to the handle of the *malleus - modulates tension on the tympanic membrane and overall transmission. it is stimulated by noise, fright, facial touch and vocalization (screaming). |
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Term
| what is the path of innervation from the inner ear to the primary auditory cortex? |
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Definition
| spiral ganglion -> cochlear nuclei -> superior olivary nucleus -> lateral lemniscus -> inferior colliculus -> inferior brachium -> medial geniculate nucleus -> primary auditory cortex (transverse temporal gyrus). *at the level of the cochlear nuclei, the innervation crosses over via the trapezoid body (cochlear nuclei to contralateral superior olivary nucleus) as well as the inferior colliculus - therefore auditory information is present at both superior olivary nuclei from a single spiral ganglion. |
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Term
| what characteristics of sound combine to create meaning? |
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Definition
| intensity, frequency, and location of stimulus (first decoded at the level of the superior olivary nucleus - via differences in frequency and time delay). |
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Term
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Definition
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Term
| what would be the result of a lesion in the trapezoid body? |
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Definition
| both superior olivary nuclei would allow hearing in both ears, but the lack of decussation would lead to an inability to locate sound. |
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Term
| what does the auditory processing occurring the the L brain cover? |
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Definition
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Term
| what does the auditory processing occurring the the R brain cover? |
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Definition
| intonation - sarcasm/humor/music |
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Term
| what is sensory aprosodia? |
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Definition
| difficulty understanding meaning conveyed by tone of voice. prosody = musical/tonal aspects of speech |
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Term
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Definition
| difficulty conveying meaning through tone of voice. prosody = musical/tonal aspects of speech |
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Term
| what is the innervation of the visual pathway? |
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Definition
| image-> optic nerve -> optic chiasm (R+L visual fields separated) -> optic tract (wraps around cerebral peduncles and sends a branch -> superior colliculi, pretectal area) -> lateral geniculate nucleus -> geniculocalcarine tract/meyer's loop -> optic radiations -> visual cortex |
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