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Hearing apparatus is a complex transducer; converts sound waves into _____________, which are suitable for analysis by the CNS.
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What are the parts of the Auditory System?
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Auditory System
| Question | Answer |
|---|---|
| Hearing apparatus is a complex transducer; converts sound waves into _____________, which are suitable for analysis by the CNS. | CODED ACTION POTENTIALS |
| What are the parts of the Auditory System? | External ear, Middle ear, Inner ear, Central Auditory Pathways |
| What is the bony labyrinth? | a series of cavities within the petrous part of temporal bone |
| What is the membranous labyrinth? | series of membranous sacs and ducts contained within the bony labyrinth |
| What are the parts of the bony labyrinth? | vestible (central part) cochlea (anterior to vestibule) semicircular canals (posterior to vestible) |
| What does the bony labyrinth contain? | Clear fluid (perilymph) in which membranous labyrinth is suspended; perilymph is rich in Na and poor in K |
| The 3 semicircular canals are perpendicular to each other and open into what? | posterior part of vestibule |
| Descibe the appearance of the cochlea. | snail shell; central pillar (modiolus) around which a hollow bony tube makes 2.5 turns, each turn is of a smaller radius; apex is anterolaterally, base is posteromedially (towards bottom of internal acoustic meatus) |
| Where is the membranous labyrinth located? what is it filled with? | located within bony labyrinth, surrounded by perilymph. It is filled with endolymph (rich in K, poor in Na) |
| Name the parts of the membranous labyrinth. | Utricle and saccule 3 semicircular ducts cochlear duct (scala media) |
| The Utricle and the Saccule are connected by what? | utriculosaccular duct |
| The endolymph duct arises from the utriculosaccular duct and traverse what? | vestibular aqueduct |
| The posterior expanded end of the endolymph duct is located where? | under the dura mater of the posterior surface of the petrous part of the temporal bone (it is a storage place for lymph) |
| Saccule is connected to cochlear duct via what? | ductus reuniens |
| Utricle and saccule contain specialized receptors (maculae) which are sensitive to the position of the head with respect to what? | gravity, linear acceleration, tilting of the head |
| The ampulla of each semicircular duct contains a specialized receptor (crista ampullaris) which is sensitive to what? | angular acceleration |
| The Cochlear duct contains a specialized receptor for hearing. Name it. | spiral organ/organ of Corti |
| The maculae and cristae ampullaries are innervated by what? | vestibular part of CN VIII |
| The spiral organ is innervated by what? | cochlear part of CN VIII |
| A cross section of the cochlea will show 3 fluid filled compartments. What does the scala vestibuli and the scala tympani contain? | The scala vestibuli and the scala tympani contain perilymph. |
| where are the scala vestibuli and the scala typani continous with one another? | at the apex of the cochlea (helicotrema) |
| What labyrinth is the cochlear duct part of? | membranous labyrinth |
| The scala vestibuli connects with __________ at the base of the cochlea and with __________ at apex of cochlea (helicotrema) | vestibule; scala tympani |
| The scala tympani spirals from the apex to the base of the cochlea. It communicated with the tympanic cavity via what? | communicated with tympanic cavity via round window (closed by secondary tympanic membrane) |
| The Cochlear Duct (Scala Media) is _________ in cross section and is separated from the scala tympani by what? | triangular; basilar membrane |
| The Cochlear Duct (Scala Media) is separated from scala vestibuli by what? | Vestibular (Reissner's membrane) |
| Where is the stria vascularis located? Describe its structure. What does it produce? | The stria vascularis lines the lateral wall of the cochlear duct. It is highly vascular and slighty pigmented. It produces endolymph that fills the membranous labyrinth. |
| What organ is the auditory receptor? Where is it located? What does it consist of? | spiral organ (of Corti); located on basilar membrane; consists of neuroepithelial receptor cells and supporting cells |
| What are the neuroepithelial cells of the Spiral Organ (of Corti)? | hair cells (50 to 100 stereocilia project from free to apical surface of cells) |
| These hair cells are arranged in 2 groups, the inner hair cells and the outer hair cells. Describe each group. | Inner hair cells --> form single row from base to apex of cochlea outer hair cells --> form 3 rows from base to apex of cochlea |
| Once damaged, can hair cells regenerate? | No. |
| What is the tectorial membrane? (under heading of Spiral Organ of Corti) | The tectorial membrane is a gelatinous structure that extends over hair cells --> tips of stereocilia are embedded in (or brush) tectorial membrane |
| Are stereocilia arranged in curving rows or are they straight? Are they polarized or unpolarized? | stereocilia are arranged in curving rows and are polarized |
| Where are the longest stereocilia located? | The longest stereocilia are located on the outer part of the cell (toward stria vascularis) --> as one moves inward (toward modiolus) stereocilia become shorter |
| Outward deflection of stereocilia (towards longest stereocilia or stria vascularis) causes what? | depolarization of hair cell |
| Vibrations reaching the base of the stapes are transferred to what? | perilymph of scala vestibuli |
| When the footplate of stapes moves in, secondary tympanic membrane ____________. when footplate moves out, secondary tympanic membrane is drawn __________. | bulges out; drawn inward |
| Displacement of perilymph by inward movement of stapes causes ___________________ of basilar membrane. Outward movement of stapes causes ___________. | downward deflection; upward deflection |
| Sounds of different frequencies cause waves in basiliar membrane with maximal amplitude (maximal membrane displacement) at different points along the membrane. What is this known as? | tonotopic representation |
| High frequency sounds cause waves of maximal amplitude close to the ________ of the cochlea. | base |
| Low frequency sounds cause waves of maximal amplitude close to the _________ of cochlea. | apex |
| Is tonotopic representation maintained through the auditory pathway? | yes |
| Hair cells are very sensitive transducers --> convert mechanical forces applied to stereocilia into ___________________. | electrical signals |
| With upward movement of the basilar membrane, stereocilia are deflected __________________. | outward (towards stria vascularis) |
| Tension causes the opening of what? | mechanically gated ion channels (selective to K) --> K enters the cell following an electrical gradient --> depolarization of hair cell ensues. |
| Depolarization opens what? | voltage-sensitive Ca channels --> Ca enters cell --> further depolarization and increased intracellular Ca |
| Increased intracellular Ca leads to what? | Binding of glutamate-containing vesicles to cell membrane at base of hair cell. There is then a release of glutamate into the synaptic cleft b/t the hair cell and the cochlear nerve (afferent/sensory fibers) |
| The sensory fiber is then depolarized. The action potential is transmitted along the ____________ to the __________. | cochlear nerve; brainstem |
| The cell bodies of sensory neurons that innervate hair cells of the spiral organ form what, which is located within the modiolus? | spiral ganglion |
| The sensory neurons of the spinal ganglion are what type of neurons? | bipolar neurons |
| There are two types of sensory neurons: Type 1 cells and type 2 cells. Which type is more abundant? | type 1 hair cells make up 90-95% of cells in spiral ganglion |
| A type 1 hair cells' peripheral processes (dendrites) synapse with how many inner hair cells? | only 1 or 2 inner hair cells; each inner hair cell is contacted by dendrites of 20 or more type 1 sensory neurons; most auditory information conveyed to CNS originates from inner hair cells. |
| What hair cells do type II cells innervate? How many hair cells do type II cells innervate? | outer hair cells; 10 or more outer hair cells; each other hair cell is contacted by dendrites of approximately 4 Type II sensory neurons. |
| Auditory Pathway: Nerve impulses pass through at least ________ from receptor to cerebral cortex. | 4 neurons |
| What are the first order neurons? | spiral ganglion |
| What are the second order neurons? | anterior and posterior cochlear nuclei |
| What are the third order neurons? | inferior colliculus |
| What are the fourth order neurons? | medial geniculate nucleus |
| True or False: There are some additional nuclei (between 2nd and 3rd neurons) where some fibers synapse | True |
| In auditory pathway above cochlear nuclei, information from _________________ ear predominates, but they carry _______ information. | contralateral; bilateral (imput from both ears ascends on the right and on the left sides of the brainstem, and reaches auditory cortex of right and left cerebral hemispheres) |
| Where are the 1st order neurons located? What type of neurons are they? What do their peripheral processes synapse with? | -located in spiral ganglia -are bipolar neurons -peripheral processes synapse with hair cells of spiral organ |
| What do the central processes (axons) of the 1st order neurons do? | form the cochlear division of CN VIII |
| How does the cochlear division of CN VIII travel? | It enters cranial cavity via internal acoustic meatus and attaches to brainstem at the lateral end of pontomedullary junction (cerebellopontine angle) |
| Cochlear nerve fibers synapse with 2nd order neurons where? | in anterior and posteror cochlear nuclei, located on lateral and posterior surfaces of restiform body, respectively, at pontomedullary junction. |
| Fibers from the posterior cochlear nucleus and some from the anterior cochlear nucleus form what? | Posterior acoustic stria --> passes behind restiform body, decussates and ascends to contralateral inferior colliculus in lateral lemniscus. |
| Most fibers from the Anterior Cochlear Nucleus pass anterior to the restiform body and terminate in . . . | ipsilateral and contralateral superior olivary nuclei (fibers crossing midline to end in contralateral superior olivary nucleus form a fiber bundle known as trapezoid body) |
| Where is the superior olivary nucleus located? Where does it receive fibers from? | -anterior part of the tegmentum of lower pons -ipsilateral and contralateral anterior cochlear nuclei |
| The Superior olivary nucleus gives rise to fibers that that ascend largely in what? | ipsilateral lateral lemniscus |
| What does the superior olivary nucleus play an important role in? | localization of sounds in space |
| Fibers of the lateral lemniscus terminate where? | inferior colliculus |
| Fibers from the medial geniculate nucleus form what? | auditory radiations; these pass inferior to lentiform nucleus (sublenticular limb of internal capsule) and terminate in primary auditory cortex. |
| Where is the primary auditory cortex? | transverse temporal gyri (Brodman's areas 41 and 42) -> superior surface of temporal lobe (floor or lateral fissure) |
| The nucleus of the trapezoid body is found between the cochlear nuclei and the inferior colliculus. What does it consist of? What fibers does it recieve? where does it send fibers to? What does it do? | -consists of neurons located among fibers of trapezoid body -receives fibers from contralateral anterior cochlear nucleus -sends fibers to ipsilateral superior olivary nucleus -helps superior olivary nucleus in localizing sounds in space. |
| Where is the nuclei of the lateral lemniscus located? What fibers does it recieve? What does it send fibers to? | -Groups of neurons located within lateral lemniscus in upper pons -Receives fibers from lateral lemniscus -sends fibers to ipsilateral and contralateral inferior colliculi |
| What do brainstem auditory evoked potentials do? | make it possible to follow the sequence of electrical events in the auditory pathways from the cochlea to primary auditory cortex |
| Explain the procedure of brainsteam auditory evoked potentials. | place scalp electrodes -> click sounds -> computer separates responses along the auditory pathways -> 7 averaged out waves detected |
| Pathology anywhere along the way results in what? | reduction or absence of the waves above the level of the lesion. |
| What are brainstem auditory evoken potentials commonly used for? | Used for suspected lesions at the cerebellopontine angle or higher levels of auditory pathways, as well as in the medico-legal domain, to access claims of deafness from environmental noise in industry. |
| Define conduction deafness (conduction hearing loss): | results form any interference w/ passage of sound waves through external or middle ear (ex. serous otitis media, otosclerosis) |
| Define nerve deafness (sensorineural hearing loss): | results from damage to receptor cells in spiral organ, cochlear nerve, or cochlear nuclei (ex. ototoxic drugs, acoustic neuroma) |
| Why do unilateral lesions to the auditory cortex or auditory pathways distal to the cochlear nuclei cause no significant hearing loss? | because of bilateral representation -> they only produce subtle hearing impairments (inability to localize direction and distance of sounds) |
| What does the Rinne's Test determine? How is it performed? | bone conduction vs. air conduction; vibrate-stem on mastoid until pt cannot hear-move out to air condu-should be able to hear for ~ 15 secs; if not 15 sec, external or middle ear is dysfunctional. |
| The Weber's test is an adjunct to the Rinne's test. Describe how it is performed. | base of vibrating tuning fork put on midline structure; pt is asked if its equal or different in both ears. Normal individual it is equal in both ears. |
| When performing the Weber's test, a patient who has a nerve deafness will have what result? | sound is louder in NORMAL ear |
| When performing the Weber's test, a patient who has conduction deafness will have what result? | sound is louder in AFFECTED ear |
Created by:
Lisa1585