Auditory system Flashcards
what is the pinna also known as?
auricula
What is the external auditory meatus?
osseous part of the external ear
What is the external auditory canal?
consists of osseous and cartilage of the external ear
what is the function of the external ear?
collect air, conduct sound, waves and allow access to the tympanic membrane
What is the middle ear also known as?
tympanic cavity
What are the ossicles of the middle ear?
malleus
Incus
Stapes
What are the openings of the osseous labrinth of the inner ear?
oval window
round window
what is another name for the oval window?
fenestra vestibuli
what is another name for the round window?
fenestra cochlea
What covers the oval window?
foot plate of the stapes
what covers the round window?
secondary tympanic membrane
Where are vibrations of the tympanic membrane transferred?
transferred through the ossicular chain to the oval window and leads a pressure change in the inner ear
what are the muscles of the ear?
tensor tympani muscle
stapedius
what innervates the tensor tympani muscle?
V nerve
What innervates the stapedius muscle?
VII nerve
What is the function of the muscles of the ear?
dampen/ attenuate movements of ossicles and tympanic membrane in response to high intensity sounds
what are the two portions that make up the inner ear?
osseous and membranous labyrinths
What is the osseous labyrinth?
consists of a system of interconnecting spaces located in the petrous part of the temporal bone
What fills the osseous labyrinth?
perilymph
what are the parts of the osseous labyrinth?
semicircular canal (posterior)
Vestibule (middle)
cochlea or cochlear canal (anterior)
What is the central bony axis of the cochlea called?
modiolus
How many turns does the cochlea do around the modiolus?
2.75
What is the membranous labyrinth?
Consists of a series of interconnecting membrane tubes that are suspended within the spaces of the osseous labyrinth
What is the lumen of the membranous labyrinth filled with?
endolymph
what are the parts of the membranous labyrinth/
semicircular ducts
utricle
saccule
cochlear duct
Where are the utricle and saccule found?
within vestibule of osseous labryinth
What 3 parts is the cochlear canal divided into?
scala media
scala vestibuli
scala tympani
What is the scala media?
cochlear duct which forms the middle space
what is scala vestibuli?
space superior to the scala media filled with perilymph
What is the scsala tympani?
interior to the scala media filled with perilymph
what is the small opening where at the apex of the cochlea where the scala tympani and scala vestibuli communicate known as?
helicotrema
what window is the scala tympani continuous with?
Round window
Do all three scala spiral up the cochlear canal?
Yes, all three scala spiral up the cochlear canal
What is the cochlear duct?
membranous duct suspended in the middle of the cochlear canal
What are the three wall borders of the cochlear duct?
vestibular membrane
stria vascularis
basilar membrane
what is the vestibular membrane also known as?
Reissner’s membrane
What does the vestibular membrane do?
separates the scala media from the scala vestibuli
what is the stria vascularis?
the outer wall that includes an epithelial lining over vascular connective tissue
what does the stria vascularis do?
produces endolyph that fills the membranous labyrinth
what is the basilar membrane?
separation between the scala media and the scala tympani
what is included in the basilar membrane of the cochlear duct?
(spiral) organ of corti
What is the organ of corti?
specialized mechano receptor for auditory information
How does the organ of corti travel?
It extends continuously along the spiral turns of the cochlear duct (basal membrane)
what are the support cells of the organ of Corti?
Border cells, phalangeal cells, pillar cells and cells of Hensen
What is the tectorial membrane?
gelatinous membrane continuous along the organ of corti where tips of the hair cells are embedded into the membrane
What are the sensory cells of the organ of corti?
hair cells (receptor cells of organ of cortis)
what are the two types of sensory cells in the organ of corti?
inner hair cells and outer hair cells
what is the presentation of the inner hair cells?
Single row consisting of 7000 cells
What is each inner hair cell connected to?
each cell is engaged at its base by terminals of fibers of the cochlear nerve (division of VII nerve)
What is the presentation of outer hair cells?
multiple rows consisting of about 25000 cells
what are the “hairs” of inner and outer hairs?
modified microvilli that extend from the apical end of the cells and are embedded in the tectorial membrane
What happens to the outer hair cells when the basilar membrane vibrates?
The hairs bend in relation to the tectorial membrane, and changes the excitability of the hair cells and generates auditory information relayed in the sensory fibers of the cochlear nerve (towards the brain)
With the activation of the organ of corti what occurs first?
Movement of the footplate of the stapes at the oval window initiates corresponding pressure waves in the lymph
After footplate movement what occurs with organ of corti activation?
waves initiate movement of the secondary tympanic membrane opering the round window and of the basillar membrane
What occurs after the moment of the secondary tympanic movement
The specific part of the basilar membrane that vibrates maximally is dependent on the pitch of the sound
is the organ of corti organized tonotopically?
yes it is
what is important about the organ of corti in regards to pitch?
The pattern of organization is that high pitch sounds are in the basal turn and low pitch sound are monitored near the apical end
what is the normal range of frequency for human hearing?
20-20000 Hz
what can repeated exposure to excessively loud noises cause?
High frequency deafness due to degeneration changes of the corti at the basal turn
What is the primary neurons of the auditory pathways?
cell bodies of primary cochlear neurons comprise the Spiral ganglia positioned in spiral fashion in the modiolus along the turns of the cochlear duct
What do most peripheral processes of the auditory pathway do?
innervate hair cells
what do the central processes of the auditory pathway travel and how?
They are included in the VIII nerve and traverse the internal acoustic meatus to reach the brainstem
Where do central processes of the auditory pathway terminate?
In the rostral medulla at dorsal and ventral cochlear nuclei
What are the secondary neurons of the auditory pathway?
cell bodies in the cochlear nuclei
Where do processes from the cohlear nuclei of the auditory pathway travel?
processes of these neurons project rostrally through the central auditory pathway
What is is included in the process of the cochlear nuclei of the auditory pathway?
1) Contralateral and ipsilateral projections
2) the ascending auditory pathway is bilateral and determines the auditory information that originated from one ear and is projected to auditory cortex in both cerebral hemispheres
Can secondary neurons (cochlear nuclei) of the auditory pathway project axons to the contralateral side of the pons?
Yes, it can
what are the decussating fibers of the contralateral pathway of the auditory pathway known as?
trapezoid body
Where do some of the fibers of the contralateral pathway of the auditory pathway terminate from the cochlear nucleus?
superior olivary nucleus
What do the ascending fibers from the superior olivary nucleus to the inferior colliculus of the auditory pathway form?
lateral leminscus
where do the processes in the lateral lemniscus terminate?
terminate in the inferior colliculus
Where do fibers from the inferior colliculus of the contralateral pathway of auditory pathway travel and terminate?
from neurons of the inferior colliculous traverse the interior brachium and terminate in the medial geniculate body of the thalamus
Where do the neurons of the medial geniculate body project for the contralateral pathway of auditory pathway and where do they terminate?
Neurons of the medial geniculate body project axons through the posterior limb of the internal capsule and terminate in the primary auditory cortex in the temporal lobe
what are the projecting fibers of the auditory pathway from the medial geniculate body to Heschl’s gyrus known as?
auditory radiations
Do some secondary neurons in the ventral cochlear nucles project axons to the ipsilateral superior olivary nucleus?
Yes, this is known as the ipsilateral pathway
what is the pathway for auditory information ascending in the ipsilateral pathway/
rostral movement through the ipsilateral lateral lemniscus, inferior colliculus, inferior brachium, medial geniculate body and auditory radiations to the primary auditory cortex
where is the auditory cortex found?
Located in the floor of the lateral sulcus along the superior temporal gyrus
what is the transverse temporal gyrus also known as?
Heschl’s gyrus
what brodmann’s map areas is the auditory cortex located in/
41, 42
What is the function of the auditory cortex?
permits audition (hear sounds)
where is the auditory association cortex found?
anatomical areas include areas of the temporal lobe that surrounds the primary auditory cortex
What brodmann’s map rea is the auditory association cortex located in/
22
what is the function of the auditory association cortex/
permits recognition and interpretation of various qualities of sounds based upon one’s previous experiences
What is the clinical significance of a bilateral ascending auditory pathway?
There can be different clinical presentations depending on where damage occurs along these pathways.
What would unilateral damage to the ascending auditory pathway above the cochlear nuclei result in?
Slight decrease in both ears and can be difficult to detect
What would unilateral damage to the ascending auditory pathway peripheral to the the cochlear nuclei result in?
ipsilateral ear decrease or loss of hearing and extent of loss depends upon extent of damage
What do disturbances of the peripheral auditory receptor apparatus result in/
conductive hearing loss
What do interruption of the VIII nerve or elements of the central auditory pathway in the brain result in?
Neural hearing loss
When an unexpected loud noise occurs a reflex orientation occurs, list the pathway.
inferior colliculus -> superior colliculus -> (via tecto bulbar fibers to CN III, IV, IV for eye motion) and/or (via tectospinal fibers to the spinal cord onto motor neurons for the head and neck movements)
