Auditory and Vestibular System Flashcards
Compare endolymph to perilymph in terms of potassium concentration, which end of hair cells it contacts, and where it is found
Endolymph — potassium-RICH fluid filling cochlear duct and membranous labyrinth; bathes APICAL end of hair cells. Found in SCALA MEDIA.
Perilymph — potassium-POOR fluid filling bony labyrinth; bathes BASAL end of cochlear hair cells. Found in SCALA VESTIBULI and SCALA TYMPANI.
In terms of regions of the basilar membrane and position of oval window vs. helicotrema, where are high frequency vs. low frequency sounds registered?
High frequency sounds = near oval window, where basilar membrane is narrow and stiff
Low frequency sounds = near helicotrema where basilar membrane is wide and flexible
Hair cells are mechanoreceptors that are stiff, graded in size, and rich in actin. Stereocilia exist on their ___ surface, while neural synapses are on the ______ surface
Apical; basal
Following deflection of stereocilia, ____ ions enter the cell from endolymph and depolarize it.
K+
Following deflection of stereocilia, K+ ions enter the cell from endolymph and depolarize it.
The electrochemical gradient driving this results from what 2 factors?
Large endolymphatic potential (K+ concentration gradient)
Large electrical gradient (scala media has high positive charge)
Deflection of stereocilia causes depolarization, release of NT _______ and generation of APs in CN 8. Stereocilia are linked together and deflect as a bundle. Deflection toward the tallest stereocilia causes _____ while deflection in the opposite direction causes _____
Glutamate; depolarization; hyperpolarization
What are the ion channels in the hair cells that allow K+ in to initiate depolarization?
TRPA1
Activation of TRPA1 and influx of K+ allows voltage gated ____ channels to open which is what triggers release of _____ at the postsynaptic cell, a spiral ganglion neurite
Ca; glutamate
What structure maintains the electrochemical properties of the endolymph?
Stria vascularis
Difference in function between inner hair cells vs. outer hair cells of basilar membrane
Inner hair cells = type I afferents; primary source of auditory info (transmission)
Outer hair cells = type II afferents; amplification
In terms of hair cell innervation, hair cells receive afferent innervation from the ____ _____ and efferent innervation from the _____ ____ ____
Spiral ganglia; superior olivary complex
Function of dorsal cochlear nuclei
Determine location of sound
Function of ventral cochlear nuclei
Determine nature of sound (high vs. low frequency)
Function of medial superior olivary nucleus (primary nucleus of superior olivary complex)
Difference in TIME of arrival to ears
Function of lateral superior olivary nucleus
Differences in INTENSITY
Function of superior colliculus vs. inferior colliculus
SC: takes location data from IC and adds final dimension (vertical height) to create spatial map of sounds location
IC: Suppresses info related to echoes, which would interfere with localization and arrives at a final estimation of localization of sound along horizon
Function of primary auditory cortex (A1) vs. association (A2)cortex
A1 = Beginning to interpret sound
A2 = processing complex sounds, name sounds, speech undulations
First site in brainstem where information from both ears converges
Superior olivary complex
Relay station in auditory pathway located in the thalamus, allows processing of speech inflections
Medial geniculate nucleus
In the tonotopic map of the primary auditory cortex, more rostral areas are activated by ____ frequencies while more caudal areas respond to _____ frequencies
Low; higher
3 types of efferent input to the auditory system
Olivocochlear efferents
Middle ear muscle motor neurons
Autonomic innervation of inner ear
Olivocochlear efferents originate in the superior olivary complex
Medial OC neurons innervate ____ hair cells while lateral OC neurons innervate ____hair cells
The main function of these efferents is ______
Outer; inner
Protective
[shifts responses to higher sound levels]
Function of middle ear efferents
Tensor tympani to the malleus (from CN V)
Stapedius to the stapes (from CN VII)
May prevent damage and prevent low frequency masking which improves speech discrimination
What are otoacoustic emissions? What are their clinical importance?
The ear can emit sound — either spontaneous or evoked. Spontaneous occur in 1/3 of people and evoked are used to test for hearing loss
Clinically important for newborn hearing screen, tinnitus, and ototoxicity
Type of hearing loss caused by damage to hair cells or nerve fibers or both
Sensorineural hearing loss
[caused by noise damage, ototoxic drugs, age]
Which type of hair cells are more susceptible to injury in terms of sensorineural hearing loss? Which area of the cochlea is more susceptible?
Outer hair cells
Base (high frequency) of cochlea is more susceptible
What structures detect rotational acceleration vs. forward/backward linear acceleration vs. vertical linear acceleration?
Rotational acceleration (horizontal, anterior, posterior) = semicircular canals
Horizontal linear acceleration = utricle
Vertical linear acceleration = saccule
Rotation in the horizontal plane is best detected by what ear structure?
Horizontal semicircular canal
Rotation in the vertical plane backwards maximally activates what ear structure?
Posterior semicircular canal
Rotation in the vertical plane forwards maximally activates what ear structure?
Anterior semicircular canal
Regardless of which direction we fall, our reflexes are designed to keep out eyes on the _______
Horizon
[while rotating, our eyes rotate horizontally, if you fall forward your eyes move up, if you fall backward your eyes move down]
When the horizontal semicircular canal is active, the ipsilateral _____ m. is activated while the ipsilateral ______ m. is inhibited
Medial rectus; lateral rectus
When the posterior semicircular canal is activated, the _____m. is activated while the ____ m. is inhibited so that the eyes move down to continue to focus on a point as you fall backwards
Superior oblique; inferior oblique
When the anterior semicircular canal is activated, the ____ m. is activated and the _____ m. is inhibited so that the eyes move up to continue to focus as you fall forward
Superior rectus; inferior rectus
________ resides inside the vestibular apparatus (in the membranous labyrinth)
_______ surrounds the vestibular apparatus (in the bony labyrinth)
Endolymph (high [K+])
Perilymph (high [Na+])
The vast majority of the cortical and cerebellar involvement of the vestibulooptic reflexes is to _____ the reflex to allow for voluntary motion
Suppress
