Ch 14: Hearing Flashcards
what is the functional component of CN 8?
SSA
sound consists of ?
sinusoidal waves- alternating condensations and rarefactions- of air molecules
the frequency of the waves is measured in?
frequency determines?
measured in Hz
determines pitch of the sound
the amplitude of each wave is measured in?
amplitude relates to?
measured in decibels (dB)
relates to the loudness of the sound
the human ear can detect sound frequencies from ____ and loudness from _____?
frequencies: 20 - 20,000 Hz
loudness: 1 - 120 dB
what are the 3 components of the auditory apparatus?
external ear
middle ear
inner ear
these components occupy 3 spaces in the skull, separated solely by membranes
what does the external ear (auricle) lead to?
the external auditory meatus
what separates the external auditory meatus from the cavity of the middle ear?
the tympanic membrane
what are the 3 ossicles that span the middle ear?
malleus
incus
stapus
what does the malleus attach to?
the tympanic membrane
what does the stapes attach to?
the oval window through a ligamentous membrane on its footplate
what does the oval window do?
separates the air filled middle ear cavity from the fluid filled inner ear cavity
provides an opening into the vestibule portion of the inner ear which contains perilymph
what happened when sound mediated by air strikes the tympanic membrane?
it induces motions in this membrane that the ossicles convey to the oval window
the chain of these 3 ossicles in the middle ear serves as an amplifier as well as an impedance-matching device that decreases the amount of energy lost by the sound waves in going from air to the fluid (perilymph) behind the oval window
what is continuous on either side of the vestibule of the inner ear?
vestibule consists of a chamber that is continuous on one side with the cochlea and on the other side with the semicircular canals
what is the cochlea?
a perilymph-containing tube
resembles a snail shell
about 3.5 cm long wrapped around itself in 2.5 turns
the cochlea, semicircular canals and the vestibule make up the:
what lies within it?
these 2 connected chambers within the temporal bone of the skull make up the bony labyrinth
a membranous labyrinth lies within the bony and contains endolymph
what is the modiolus?
a conical central bony core that forms the axis of the cochlear turns
what is the spiral lamina?
a ridge of bone turning around the moidolus, projects into the cochlear space
partially divides the cochlear cavity into two perilymphatic chambers
what are the 2 perilymphatic chambers?
1- scala vestibuli
2- scala tympani
what is the scala media or cochlear duct?
forms the membranous labyrinth within the cochlea
completes the separation of the scala vestibuli from the scala tympani
what is the organ of Corti?
contains sensory epithlium, or hair cells, forms a ribbon that stretches along the length of the cochlear duct and rests on the basilar membrane as it spirals around the turns of the cochlea
what is the helicotrema?
the apical connection between the scala vestibuli and scala tympani
the piston action of the footplate of the stapes at the oval window produces:
an instantaneous pressure wave in the perilymph of the stala vestibuli. this pressure wave travels to the helicotrema –> sets up a traveling wave on the basilar membrane.
as a result, the pressure wave produced by a sound of a specific frequency (pitch) causes the basilar membrane to vibrate maximally at a particular point along its length. this vibration maximally activates the hair cells of the organ of Corti located at that point
what are the 2 types of receptors of the organ of Corti?
inner hair cells
outer hair cells
what does inner hair cells function as?
auditory receptor cells
the base of each inner hair cell forms an indirect attachment to the basilar membrane
the apex of each cell bears stereocilia, which extend above the surface of the cell. the tips of the stereocilia lie just below the tectorial membrane
what is the tectorial membrane?
forms an attachment to the wall of the cochlear duct separately from the attachment of the basilar membrane to the boney spiral lamina
when sound waves enter the cochlea, the basilar and tectorial membranes move independently of each other and the stereocilia touch the tectorial membrane and receive shearing forces. The resultant bending of the stereocilia:
opens up ionic channels and causes changes of potential in the hair cell membrane.
synapses at the base of each hair cell activate the closely applied dendritic processes of the spiral ganglion cells.
what do outer hair cells do?
contain stereocilia embedded in the tectorial membrane, possess contractile properties.
this permits them to control the sensory response properties of the organ of Corti by regulating the apposition of the tectorial membrane to the inner hair cells.
system of efferent nerve fibers from the superior olivary complex of the pons, the olivochochlear bundle, accomplishes this important function
the organ of corti serves as a :
audiofrequency analyzer
tonotopically organized so the highest tones (in pitch and frequency) maximally stimulate the hair cells in the most basal portion of the cochlea
the cochlear nerve enters the BS at the:
pontomedullary junction
as the cochlear nerve attaches to the BS, the nerve clings to:
the lateral side of the inferior cerebellar peduncle and enters the posterior and anterior cochlear nuclei
each entering nerve bifurcates and connects synaptically with neurons in both cochlear nuclei (ventral and posterior)
what are the 3 projections that relay information from the cochlear nuclei to other structures centrally and rostrally?
dorsal, intermediate and ventral acoustic striae
what is the path of the dorsal striae?
originates in the dorsal cochlear nucleus, passes over the CIP and crosses to join the contralateral lateral lemniscus
–>contralateral inferior colliculus –> medial geniculate body–> auditory areas of the cortex
*constitutes “Monaural central auditory pathway”- carries information about the frequency of auditory signals
what is the path of the intermediate striae?
originates in the VENTRAL cochlear nucleus,
then takes a course similar to the dorsal stria (over the ICP–> contralateral lateral lemniscus–> inf colliculus–> medial geniculate)
“monaural central auditory pathway” - carries info about the frequency of auditory signals
what is the path of the ventral striae?
originates from the ventral cochlear nucleus
passes anterior to the ICP and terminates in the ipsilateral and contralateral nuclei of the trapezoid body and superior olivary nuclei
these nuclei in turn project fibers into the ipsilateral and contralateral lateral lemniscus
form bilateral “Binaural pathway” that includes synapses in the trapezoid body, superior olivary complex and the nuclei of the lateral lemniscus.
this specialized pathway can analyze the location of origin, or direction, of auditory stimuli.
also ends in the inferior colliculus which sends its axons to the medial geniculte nucleus
what does the medial geniculate nuclei serve as?
special sensory nuclei of the thalamus and constitutes the final sensory relay station of the hearing pathway
what is air conduction?
mediates sound when the source of the sound arises some distance from the ear and air transmits the sound waves to the tympanic membrane
what is bone conduction?
mediates sound when the source of the sound, a vibrating body, maintains contact with the skull or bones of the body and these bones transmit sound waves tot he ear
injury to the sensory components of the inner ear or to the fibers of the 8th nerve commonly produces:
hearing loss (sensorineural deafness)
tinnitus (ringing)
disease affecting the auditory conducting mechanisms in the middle ear may also cause:
hearing loss and tinnitus
“conductive deafness)
what is the Weber Test? how is it performed?
distinguishes sensorineural deafness from conductive
physician apples the base of a vibrating fork to the forehead in the midline and asked the pt whether the sound seems loudest in the midline or in one ear
normal hearing= loudest in midline
conductive deafness= sound louder in affected ear
because: conductive deafness, an abnormality in middle ear structures reduces sound perception by air conduction, whereas perception by bone conduction becomes relatively enhanced as a result of the inability of the ear to perceive ambient noise in the environment by air conduction
sensorineural deafness= sound louder in the normal ear
because: bone conduction of sound remains as ineffective in stimulating the damaged nerve as air conduction
what is the Rinne test? how is it performed?
compares the pt’s ability to hear a vibrating tuning fork by bone conduction and by air conduction
fork placed over 1 mastoid process and asks the pt to indicate when the sound can no longer be heard. PT removes the form from mastoid process and holds the tines of the still vibrating tuning fork in front of the ear.
normal hearing= continues to hear by air conduction after bone conduction ceases.
conductive deafness= bone conduction functions better than air conduction
sensorineural deafness= both are diminished but air conduction remains better than bone
what are audiometers?
provide refined testing of hearing because pure tones can be used at controlled intensities
sensorineural deafness commonly occurs with:
Meniere's disease trauma drug damage infection aging occlusion of the internal auditory meatus
conductive deafness may result from:
wax in the external auditory canal
otis media
diseases that impair the capacity of the ossicles to function properly
what are auditory reflexes?
involuntary responses to sound that are mediated by branches from the main auditory pathway
evoke autonomic responses
auditory reflexes by way of the tectospinal tract:
fibers project from the inferior colliculus to the superior colliculus and fibers projecting from this site downward provide auditory input by way of the tectopsinal tract
these fibers terminate on LMNs in the BS and cervical SC and supply the oculomotor system and muscles of the head and neck that respond to sound
what is the general acoustic muscle reflex?
generalized startle reflex or jerking of the body in response to a loud sudden sound
what is the auditory palpebral reflex?
consists of blinking the eyelids in response to loud sound
what is the auditory oculogyric reflex?
involves deviation of the eyes in the direction of sound
what is the cochleopupillary reflex?
consists of dilation of the pupils in response to a loud noise
