Physiology of the Auditory System Flashcards
Where is the basilar membrane displacement for high frequency noises?
at the base
where is the basilar membrane displacement for lower frequency sounds?
more apical
what is the structure of the membrane near the oval/round windows?
narrow and stiff
what is the structure of the membrane near the helicotrema?
it is wider and more flexible
how is the frequency of sound (pitch) coded?
by where along the basilar membrane there is greatest deflection
what type of cells are hair cells?
they are mechanoreceptors
what is on the apical end of hair cells?
stereocilia
what is the ion composition of endolymph?
it is high in K+ but low in Na+
where is endolymph found?
it fills the cochlear duct and the membranous labyrinth ; found in the scala media
what is endolymph produced by?
stria vascularis
what is the composition of perilymph?
it is potassium poor- low K+ but high Na+
where is perilymph found?
it is found in the scala vestibuli and scala tympani
what does the perilymph bathe?
the basal end of the cochlear hair cells
what does the endolymph bath?
the apical end of the hair cells
what happens when there is a pressure differential that will bend/ pivot the stereocilia in the direction of the longest stereocilia?
K+ ions will enter the cells and depolarize the cell
what are the specific Ca2+ ion channels that open due to a change in voltage?
TRPA1
deflection of stereocilia that causes depolarization will cause what?
release of the NT glutamate and a generation of action potentials in the 8th CN nerve fibers
what happens when there is deflection of stereocilia towards the shortest stereocilia?
hyperpolarization
what is the main role of the stria vascularis?
it maintains the electrochemical properties of the endolymph aka it keeps the scala media very highly concentrated with potassium
what forms the blood-labyrinth barrier?
the high endocochlear potential drives positively charged ions into the hair cell down its concentration gradient
what is a common source of ototoxic drug secretion into the cochlea?
the stria vascularis
what is the primary function of the inner hair cells?
these are the primary source of auditory information
what is the primary function of outer hair cells?
there are the primary cells that amplify sound waves; they are also contractile
what are the olivocochlear efferents?
when the ear itself produces a sound- movement of the basilar membrane toward the oval window and through the middle ear
what neurons innervate outer hair cells?
medial olivary complex neurons
what neurons innervate inner hair cells?
lateral olivary complex neurons
how can olivocochlear efferents be measured?
in the external auditory meatus as otoacoustic emissions (OAE)
what is the clinical significant of OAE?
newborn hearing screening, ototoxicity, tinnitus
what makes up the cochlear nuclear complex?
the ventral cochlear nuclei and the dorsal cochlear nuclei
what is the role of the dorsal cochlear nuclei?
it integrates the acoustic information with somatosensory information
what is the role of the ventral cochlear nuclei?
it begins processing the temporal and spectral features of the sound (nature of the sound- high/low)
where is the first site in the brainstem where information from both ears converges?
the superior olivary complex
what is the role of the superior olivary complex?
binaural processing
what is binaural processing essential for?
to accurately localize sound
what makes up the superior olivary complex?
the medial superior olivary nucleus and the lateral superior olivary nucleus
what is the role of the medial superior olivary nucleus?
localizes sound due to differences in TIME of arrival to ears
what is the role of the lateral superior olivary nucleus?
localizes sound due to differences in INTENSITY of sounds between ears
what is the role of the inferior colliculus?
it suppresses information related to echoes and arrives at a final estimation of localization of sound along the horizon
what is the relay station in the auditory pathway?
the medial geniculate nucleus of the thalamus
what is essential in the conscious perception of sound?
the primary auditory cortex
how is the set up of the primary auditory cortex?
more rostral areas are activated by low frequencies and more caudal areas respond to higher frequencies
the auditory (secondary) association cortex is composed of multiple areas including what?
Broca’s and Wernicke’s
what does the auditory association cortex respond to?
more complex sounds such as music, identifying (naming) a sound, and speech
where do olivocochlear efferents originate?
in the superior olivary complex
what is the primary role of the olivocochlear efferents?
they decrease basilar basilar membrane motion- reduces responses to noise- may protect hair cells from damage to intense sounds
the middle ear efferents include motor innervation to what?
tensor tympani to the malleus and tympanic membrane and the stapedius to the stapes
when do middle ear efferents act and what may they prevent?
they act at low frequencies and they may prevent damage
what is sensorineural hearing loss caused from?
damage to the hair cells or nerve fibers or both
injury to outer hair cells causes what?
decrease in sensitivity
injury to inner hair cells causes what?
it cuts off auditory input to the CNS
what is the anterior semicircular canal activated by?
rotation in the vertical plane forwards (falling forward)
what is the horizontal semicircular canal activated by?
rotation in the horizontal plane (twirling like ice skating)
what is the posterior semicircular canal activated by?
rotation in the vertical plane backwards (falling backwards)
what is the utricle activated by?
linear acceleration forward and backward (running)
what is the saccule activated by?
linear acceleration up and down (dunking a hoop)
