Physiology of Auditory and vestibular systems Flashcards
Explain how different frequencies get picked up in the cochlear duct
closer to the oval and round window the basilar membrane is narrower and stiff so it picks up higher frequencies
where as closer to the helicotrema the basilar membrane is wider and looser and is able to pick up lower frequency pitches
these are the areas where the frequencies produce the greatest amount of deflection occuring from the wave created by the sound vibration (tonotopy)
How does depolarization occur in the cochlear duct and what are some characteristics of the channels
depolarization occurs whe cation channels open at the apex of the sterocilia
these sterocillia are connected to each other via tip links that transmit a force that opens a TRPA1 channel
since these are mechanotransduction channels, they are much faster signal transduction process and dont require receptor potentials so are much more sensitive as well
Endolymph is found in what in the cochlear duct
high in K+ and low in Na+ similar to intracellular fluid
and is found on the apical ends of the hair cells in the scala media
Perilymph is found in what in the cochlear duct
low K+ and high Na+ similar to extracellular fluid
found on the basal end of the hair cells in the scala tympani and scala vestibuli
what happens when the basilar membrane is moved up or downward
upwards displacement of the basilar membrane creates a shearing force that results in lateral movement of the sterocilia that cause a depolarization
-influx of K+ causing a depolariation leading to influx of Ca+ from the voltage gate channel leading to a release of glutamate into the synaptic cleft on to the cochlear nerve
Downward displacement of the membrane creates a force that results in hyperpolarization of the hair cell thus inhibiting the signal
What are the inner vs outer hair cells purpose
Inner hair cell is important for hearing (one layer)
lateral olivary complex neurons innervate the inner hair cell
outer haircell is important for amplifying the signals that are processed by the inner hair cells (three layers)
medial olivary complex neurons innervate the outer hair cell
job of the stria vascularis
produces the endolymph with high levels of K+
done by the stratified epithelial cells that extend cytoplasmic processes and folds around capillaries
the K+ is released from the capillaries and is transported accross tightly joined cells at the strial surface into the endolymph
This creates the Blood-labyrinth Barrier (BLB) to drive the positively charged ions down their concentration gradient
What makes ototoxic drugs dangerous
they disrupt the function of the stria vascularis and diminish the endocochlear potential and impact hearing
this can be caused from carbon monoxide as well
what makes outer hair cells special
primary cells that amplify sound waves that results in the movement of the basilar membrane
these cells are also contractile making them a specialized type of epithelial cell will synapse with sensory afferent peripheral terminals and with efferent neurons as well
Otoacoustic emission
due to the motillity of the outer hair cells that cause the basilar membrane to move it causes a retrograde movement toward the oval window through the middle ear via the ossicles causing displacement of the tympanic membrane
causing it to produce sound, these can be measured in the external auditory meatus, this is done in infants to asses the function of the inner and middle ear
used for sensorineural hearing loss but cant detect auditory neuropathy though
What does the olivocochlear efferents do
reduces the electromotillity of outer hair cells
decreases basilar membrane motion
reduces responses of inner hair cells and auditory nerve fibers
What medial ear efferents help protect the cochlea during exposure to intense sounds
Tensor tympani to the malleus and the tympanic membrane: attenuates the sound
Stapedius to the stapes: attenuates sound
Bilateral response to sounds contractions decrease transmission of sound act at low frequencies may prevent damage may prevent low frequency masking
Autonomic efferents that protect the cochlea
Arise from the 8th cranial nerve
sympathetic adrenergic fibers
regulates vascular tone in blood supply to cochlea
Functions of the Dorsal and ventral cochlear nuclei
Dorsal cochlear nuclei: integrates the acoustic information with somatosensory information
Ventral cochlear nuclei: begins processing the temporal and spectral features of the sound
Functions of the medial superior and lateral superior olivary complex
both receive glutamergic input
MSO= generates a map of interaural TIME diferences to help localize the sound
LSO= generates a map of interaural intensity differences to help localize the source of a sond
Tonotopic map is maintained
Functions of the inferior colliculus
suppresses the information related to echos which would interfere with localization and arrives at a final estimation of localization of sound along the horizon
information about time and intensity differences converge into the IC to help create a precise origin of sound localization along the horizon
tonotopic map is maintained in IC
Functions of the Medial genticulate nucleus
lots of converging information allowing for processing features of speech inflections
Precise information regarding intensity, frequency, and binaural properties of sound are integrated and relayed onward
Tonotopic map is maintained
Functions of the primary auditory cortex (A1)
Essential in conscious perception of sound
higher order processing of sound (loudness, modulations in volume rate of frequency)
Tonotopic is maintained
Functions of the secondary auditory association cortex (A2)
Composed of multiple areas
less specifically organized tonotopic arrangement than the primary auditory cortex
This is thought to respond to more complex sounds (music) identifying or naming a sound and speech
What is a cochlear implant
composed of an internal and external part
internal part includes a receiver and electrode array
the reciever decodes the signal and delivers the electrical signal to the electrode array
the electrode array is inserted into the cochlea through the oval window where it sits in the cochlear duct along the afferents from CN VIII. Electrical signals anywhere along the electrode array will stimulate a particular cochlear nerve afferent along the basilar membrane. THe electrode array mimics the tonotopy of the basilar membrane and stimulates the nerve at discrete frequencies
FUnction of the anterior semicircular canal
rotation in the vertical plane forwards maximally activates it
function of the horizontal semicircular canal
Rotation in the horizontal plane is best detected
Function of the posterior semicircular canal
rotation in the vertical plane backwards maximally activates it
Function of the utricle
Utricle detects linear acceleration forward and backward
Function of the saccule
Saccule detects linear acceleration up and down
