physiology of auditory and vestibular systems Flashcards
auditory system
detects sound and uses acoustic cues to ID and locate sound sources in the environment
sound
oscillations of air pressure that vary rapidly with time
amplitude
sound pressure (intensity) specified by a scale of sound pressure level (SPL) in decibels (dB)
frequency
number of oscillations of air pressure per second (Hz)
endolymph
potassium-RICH fluid filling cochlear duct and the membranous labyrinth; bathes apical end of hair cells
- similar to intracellular fluid: high in [K+] low in [Na+]
- found in scala media
perilymph
potassium-POOR fluid that bathes basal end of cochlear hair cells
- similar to ECF: high [Na+] and low [K+]
- found in scala vestibuli and scala tympani
central axons from the primary auditory neurons of the spiral ganglion project to the brainstem via the _____
auditory nerve (part of CN VIII)
basilar membrane
allows conversion of pressure waves from ossicles
Which side of the basilar membrane is higher frequencies? How much movement?
base
maximal
Which side of the basilar membrane is lower frequencies? How much movement?
apex
minimal
What direction does the sound wave travel in the basilar membrane?
base of the cochlea to the apex
What is the base of the basilar membrane near?
oval window
What is the apex of the basilar membrane near?
helicotrema
What are the properties of the basilar membrane near the oval window?
narrow and stiff
What are the properties of the basilar membrane near helicotrema?
wider and more bendy
hair cells are ___
- mechanoreceptors
- specialized polarized epithelial cells
- basal and apical ends
- stereocilia on apical surface
- stiff, graded in size, rich in actin
- neural synapses on basal side
kinocilium
tallest cilia next to the second tallest stereocilia
What happens when stereocilia are deflected toward kinocilium?
-K+ ions from endolymph enters hair cell to depolarize it
What are the 2 factors driving electrochemical gradient?
- large endolymphatic potential (K+ gradient)
- large electrical gradient (scala media has high positive charge)
What happens when K+ enters a hair cell?
- opening of voltage-gated Ca2+ channels
- Ca2+ enters cell
- vesicle-membrane fusion
- excitatory NT released
Are stereocilia connected? If so, by what?
YES, chains called tip links, ankle links, and kinociliary links
What is the result of stereocilia reflection?
toward kinocilium = depolarization –> release of glutamate and generation of APs
away from kinocilium = hyperpolarization = inhibition
TRPA1
mechanically gated K+ ion channel on hair cells
stria vascularis
component of the scala media that maintains electrochemical properties of the endolymph
inner hair cells
single row
- primary source of auditory information
- afferents - neuron from inner hair cell to brain stem (type 1 afferent neuron)
outer hair cells
- 3 rows
- act as amplifier
- contractile (prestin)
- boost mechanical vibrations of the basilar membrane
- sensitivity and tuning of responses are susceptible to injury of outer hair cells
- otoacoustic emissions
- afferents - single neuron from multiple outer hair cells to brain stem (type II afferent neurons)
- efferents - single neuron from brain stem to multiple outer hair cells
Where are hair cells positioned?
along the length of the cochear spiral
Where do hair cells receive afferent innervation from?
spiral ganglia
Where do hair cells receive efferent innervation from?
superior olivary complex
What does the cochlear nerve branch to?
cochlear nuclear complex in the medulla - VCN and DCN
DCN
dorsal cochlear nuclei
-integrates acoustic information with somatosensory information for LOCALIZATION of sound
VCN
ventral cochlear nuclei
-begins processing the temporal and spectral features of sound
superior olivary complex
- info from both ears converge=binaural processing
- MSO = medial superior olivary nucleus - primary nucleus of superior olivary complex
- tonotopic organization
- receives excitatory (glutamate and/or aspartate) projections
MSO function
- interaural TIME differences to localize sound
- responds strongest when 2 inputs arrive simultaneously
LSO function
-generates a map of the interaural INTENSITY differences to localize sound
inferior colliculus function in hearing
- suppresses info related to echoes
- estimates location along horizontal plane
superior colliculus function in hearing
-takes localization from IC and adds vertical height to create a spatial map of the sound’s location
medial geniculate nucleus (MGN)
- thalamus
- tonotopic map
- convergence from distinct spectral and temporal pathways
- processes speech inflections
primary auditory cortex (AI)
- conscious perception of sound
- higher order processing of sound (loudness, modulations in volume, rate of frequency modulation)
- tonotopic map maintained
- rostral area - lower frequencies
- caudal area - higher frequencies
auditory (secondary) association cortex
- multiple areas (Broca’s Wernicke’s)
- less specifically organized in tonotopic arrangement
- respond to more complex sounds (music), identifying (naming) a sound, and speech
efferent input to the auditory system
- olivocochlear efferents
- middle ear muscle motoneurons
- autonomic innervation of the inner ear
olivocochlear efferents
- originate in superior olivary complex
- medial OC neurons innervate outer hair cells
- lateral OC neurons innervate inner hair cells
- shifts responses to higher sound levels
- decreases adaptation
- reduces the response to noise
- may protect hair cells from damage to intense sounds
middle ear efferents
- tensor tympani to the malleus (from CN V)
- stapedius to the stapes (from CN VII)
- bilateral response to high sound levels
- contractions decrease transmission of sound
- act at low frequncies
- may prevent damage
- may prevent low frequency masking (improving speech discrimination)
otoacoustic emissions
- ear emits sound, low intensity
- spontaneous or evoked
- spontaneous OAE in 1/3 of normal people in pure tones generated from motile outer hair cells
- evoked emissions used to test for hearing loss (no emissions evoked if there is damage)
- clinically important for newborn hearing screening, tinnitus, and ototoxicity
sensorineural hearing loss
- caused by damage to hair cells or nerve fibers or both
- noise damage, ototoxic drugs, age related, loss of unknown etiology
- OHCs are more susceptible to injury than IHCs
- base (high frequency) end of cochlea is more susceptible to damage than apical (low frequency) end
- injury to outer hair cells causes decrease in sensitivity (higher thresholds) and broader tuning
- injury to inner hair cells cuts off auditory input to CNS
- some hearing may be restored with a cochlear prosthesis
cochlear prosthesis
multiple electrode array threaded through cochlea to stimulate surviving nerve fibers
angular acceleration
- spinning, turning
- falling forward
- falling backward
linear acceleration
- moving along a line (head’s point of view)
- horizontally walking
- vertically jumping
utricle detects___
linear acceleration forward and backward
saccule detects ____
linear acceleration up and down
rotation in the horizontal plane is best detected by the ___
horizontal semicircular canal
roatation in the vertical plane backward is best detected by the ___
posterior semicicular canal
rotation in the vertical plane forward is best detected by the ____
anterior semicircular canal
What eye muscles are activated when the horizontal semicircular canal is activated?
- ipsilateral medial rectus m activated
- ipsilateral lateral rectus m inhibited
- contralateral lateral rectus m activated
- contralateral medial rectus m inhibited
What eye muscles are activated when the posterior semicircular canal is activated?
- superior oblique m is activated
- inferior oblique m is inhibited
What eye muscles are activated when the anterior semicircular canal is activated?
- superior rectus m activated
- inferior rectus m inhibited
