Physiology of the Auditory and Vestibular Systems Flashcards
Where is endolymph found?
What is the K+ concentration like?
Does it bathe the apical or basal end of hair cells?
Within the cochlear duct and membranous labyrinth.
High [K+].
Bathes apical end.
Where is perilymph found?
What is the K+ concentration like?
Does it bathe the apical or basal end of the hair cells?
Between the membranous and bony labyrinth.
Low [K+].
Bathes basal end.
What fluid is in the scala media?
Endolymph
What fluids are in the scala tympani and scala vestibuli?
Perilymph
Higher frequencies have maximal motion at which region of the basilar membrane?
Lower frequencies?
Higher - at base.
Lower - apical part.
Near the oval window the basilar membrane is narrow and stiff. What sounds are absorbed best here?
High frequency sounds
Distal from the oval window the basilar membrane is wide and flexible. What sounds are absorbed best here?
Low frequency sounds
What kind of receptors are hair cells?
Mechanoreceptors
What causes an influx of K+ into the hair cells?
A deflection toward the kinocilium
What are the 2 factors that cause influx of K+ into the hair cell?
Large endolymphatic potential (high K+ conc in the cell).
Large electrochemical gradient (scala media has high + charge).
What NT is secreted once the hair cells are depolarized?
Glutamate
What happens when the stereocilia are deflected away from the kinocilia?
The cell is hyperpolarized
What ion causes depolarization of the hair cells?
What does depolarization cause the entry of?
What channel does it use?
K+
Ca++
TRPA1
Main function of scala vascularis:
Maintain electrochemical properties of endolymph
How many rows of inner hair cells?
What is their function?
1 layer.
Primary source of auditory info.
How many rows of outer hair cells?
Main function(s)?
3 layers.
Amplifier, otoacoustic emissions,
Where do hair cells receive afferents?
Where do they receive efferents?
Afferents from spiral ganglia.
Efferents from superior olivary complex.
What neuron fibers do inner hair cells use?
What neuron fibers do outer hair cells use?
Type I
Type II
Dorsal cochlear nuclei function:
To integrate acoustic info w/ somatosensory info for localization of sound.
Ventral cochlear nuclei function:
Begins processing the temporal and spectral features of the sound.
What nerve branches to reach the DCN and VCN?
Cochlear n.
What is the first site in the brainstem that info from both ears converge?
Superior olivary complex
What is the primary nucleus of the superior olivary nucleus?
Medial superior olivary nucleus
What is the main function of the medial superior olivary complex?
To generate a map of interaural time differences, which helps to localize the sound.
What is the primary function of the lateral superior olivary complex?
Generate a map of interaural intensity differences, which helps to localize the sound.
What does the superior colliculus add to the sound?
The final dimension (vertical height) to create a spatial map of the sound’s location.
What does the inferior colliculus do?
Suppresses info related to echoes, which would interfere with localization.
What is the relay station of the thalamus for the auditory pathway?
The medial geniculate nucleus
Main function of the primary auditory cortex (AI)
It is essential in conscious perception of sound and more higher order processing. Basically, beginning to interpret sound.
Anterior (rostral) areas of the primary auditory cortex (AI) are activated by?
The posterior (caudal) areas?
Apex of cochlea (low frequency)
Base of cochlea (high frequency)
Roles of the auditory (secondary, A2) association cortex (3)
Responding to more complex sounds.
Naming a sound.
Speech.
3 components of efferent input to auditory system
Olivocochlear efferents
Middle ear muscle motoneurons
Autonomic innervation of inner ear
Olivocochlear efferents begin at:
End at (medial OC neurons and lateral OC neurons):
Begin at superior olivary complex.
Medial - outer hair cells. Lateral - inner hair cells.
Functions of olivocochlear efferents (4)
Shifts responses to higher sound levels.
Decreases adaptation.
Reduced response to noise.
May protect hair cells.
Middle ear efferents include:
Main role:
CN V (tensor tympani m.) CN VII (staoedius m.)
Prevents damage by responding to high sounds.
Otoacoustic emissions
What is a positive test?
Sounds emitted by ear.
Can be spontaneous or evoked.
Positive test is no evoked emissions.
Which cells are more susceptible to injury in sensorineural hearing loss?
Outer hair cells
Cochlear prosthesis
Multiple elctrodes are threaded thru cochlea to stimulate surviving nerve fibers.
What do semicircular canals detect?
Rotational acceleration
Utricle detects:
Linear acceleration forward and backward.
Saccule detects:
Linear acceleration up and down.
Rotation in horizontal plane is best detected by:
Horizontal semicircular canal
Rotation in the vertical plane backwards (falling back) maximally activates:
Posterior semicircular canal
Rotation in the vertical plane forwards (falling forward) maximally activates:
Anterior semicircular canal
Falling back activates which muscle?
Inhibits which one?
Activates SO m. and inhibits IO m.
Falling forward activates which muscle?
Inhibits which one?
Activates IO m. and inhibits SO m.
Which fluid resides in the vestibular appatus?
Which surrounds it?
Endolymph is within it.
Perilymph surrounds it.
