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Hearing for Neuro

Neuro Exam 2- Hearing

QuestionAnswer
What makes up the outer ear? Auricle (pinna) EAM Tympanic Membrane
What is the middle ear aka? What makes up the middle ear? Tympanic cavity Connects to nasopharynx via Eustachian tube & with mastoid air cells Round & Oval windows separate middle from inner ear 3 bony ossicles- hammer, anvil, stirrup
Anatomical Parts for Hearing Cerebellopontine angle- site of acoustic neuroma (CN 5, 7, 8) Internal acoustic meatus & auditory canal- CN 8 travels with 7 Tympanic membrane Middle ear ossicles Oval & Round windows
Inner ear (Labyrinth) Cochlea, Vestibule (Utricle & Saccule), 3 Semi-Circular canals, Bony labyrinth, Membranous labyrinth, Scala vestibuli & tympani
Bony Labyrinth Surrounds membranous labyrinth Filled with perilymph, which suspends the membranous labyrinth
Membranous Labyrinth Cochlear duct, Utricle, Saccule, & 3 semi-circular canals Only the cochlear duct is our concern for hearing
Pathway for Acoustic Vibrations Acoustic Vibrations -> Scala vestibuli -> Cochlea -> Scala tympani -> Round window Vibrations also reach the scala media (cochlear duct)
Organ of Corti Hair cells of the cochlea, basilar & tectorial membranes
Higher Frequency sounds go where? Oval Window
Lower frequency sounds go where? Cochlear Apex
What are sound waves transmitted by? Tympanic Membrane
Sound waves are amplified by? Middle ear ossicles Mvmts dampened by tensor tympani & stapedius Muscles attached to 3 bones
After hitting the bony ossicles, sound waves go where? Oval window, then on to inner ear structures
Two inner ear structures receive vibrations 1. Oval window the scala vestibuli->End of cochlea joins scala tympani-> out thru round window (occurs whether sound heard or not) 2. Scala media- mechanoreceptor cilia activated by mvmt of basilar membrane relative to stiff tectorial membrane
The basilar membrane is? Tectorial membrane? Soft & elastic Stiff & rigid
Where do hair cells attach? Tops of hair cells attach to tectorial membrane, bottom of hair cells attach to basilar membrane axons. Scala vestibuli in motion from vibration, mvmt transmitted across organ of Corti, mvmt of fluid in coch duct from vibration, goes to axons/nn/hair cell
Where is pressure equalized? Eustachian Tubes
If you hear something what is the pathway? EAM->Tympanic Membrane-> 3 ossicles-> Oval window-> Scala vestibuli-> Scala media-> Scala tympani->Round window
If sound is not heard what part of the pathway is eliminated? Scala Media
Components of the Cochlea 3 compartments separated by bony shelf/membranes Scala media contains auditory end organ Oval window & round window separate, respectively, scala vestibuli & scala tympani from middle ear
Another name for the scala media is what? Cochlear Duct- contains endolymph
Where is the organ of Corti? "Sits" on the basilar membrane
Tectorial Membrane Gelatinous, extends over free surface of organ of Corti Hairs of hair cells are attached to this membrane
What occurs when vibrations in endolymph are transmitted to the tectorial membrane? Deformation of hairs attached to it, which initiates impulse in afferent nerve fibers in contacct with basilar part of hair cells
Do lesions in the CNS proximal to the cochlear nuclei result in unilateral hearing loss? NO Hearing is bilateral, once signals are in this far, it's really hard to be unilaterally deaf. There are lots of crossings, another reason it's hard to get a central lesion & become completely deaf
Cochlear Nerve Nuclei & Central Connections- Hearing Pathway Cochlear Nucleus->Trapezoid Body & Superior Olivary Nucleus-> Lateral Lemniscus/Nuclei-> Inferior Colliculus of midbrain-> Medial Geniculate Body-> Acoustic Radiation-> Auditory Cortex of Sup. Temp. Gyrus
After sound is processed, when is it actually "heard"? When impulses reach Heschl's Gyrus
What does decoding language require? Primary, Secondary, & Association cortices
Localization of Sound Begins in superior olive & inferior colliculus. Requires auditory assn areas in superior temporal gyrus & posterior parietal cortex
Unilateral Lesion Wouldn't interfere with other impulses from both ears projecting to the cortex of opposite hemisphere. Deafness in one ear usually signifies damage to the acoustic nerve, cochlea, or the sound- conducting apparatus of middle ear on that side.
3 routes for sound waves to reach inner ear 1.Ossicular- AIR conduction 2. Air Route- ossicles no longer vibrate; vibrations transmitted thru air in middle ear to round window (not effective) 3.Bone route- conducted via bones in skull to perilymph of inner ear. Used by people who use hearing aids
Sensorineural Deafness Injured Nerve
Conductive Deafness Cerumen/blockage preventing sound from getting into the ear
Weber Test Tuning fork on skull vertex; Pt report louder side. Normal= tone equal bilaterally. Sensorineural loss- louder on normal side; Conductive loss- louder on affected side
Rinne's Test Fork over mastoid (BC) & outside ear canal (AC); AC shoulder be 2x > BC Conductive loss- BC > AC Sensorineural loss- AC>BC but hearing decreased in affected ear
Audiomotor Reflex Hear a sound, have a motoric response; motoric response- contraction of tensor tympani & stapes No conscious control over this
General Acoustic Reflex If someone drops something loudly, you startle/jump Sensory = sound Motor = Jumping/Startling
Auditory Palpebral Reflex Sound causes you to blink CN 7
Auditory-Oculogyric Reflex Someone walks in a room, you look at the door
Cochleopupillary Reflex Hear something, your pupils either dilate or first constrict then dilate CN 3
Role of tectospinal tract in auditory reflexes Fiber tract from just above midbrain into spinal cord Pathway that many reflexes use. Get on the path & either go up or go down Tract is a transport system!
Created by: 1190550002