Vestibular and Auditory (2) Flashcards
A complex sound can be decomposed into what? How is it perceived?
spectrum of pure tones, each of a different frequency, no dominant rhythmicity get perceived as noise, hisses, or scratches; it is a pitch when there is a dominant rhythmicity
What is the measure of sound intensity?
decibel
What conduction properties and medium results in low impedence?
air, sound waves have low pressures and cause large
displacements of air molecules
What conduction properties and medium results in high impedence?
water, sound waves have high pressures and cause
small displacements of molecules
Mismatch in impedance causes what?
reflection of sound at an interface
What is necessary in order for the sound waves traveling through air to pass into the fluid of the cochlea?
pressure on the oval window must be greater than the pressure on the tympanic membrane; need ossicles to amplify
Increasing the force on the membrane is achieved how?
arm of malleus to which tympanic membrane is attached is longer than arm of the incus to which the stapes is attached-> lever action-> slight amplification of the sound pressure
Reducing the surface area of the membrane is achieved how?
surface area of oval window less than tympanic membrane; same force exerted on both-> smaller receives greater pressure
The middle ear does what to the sound force at the
oval window ? air molecule displacement?
magnifies 1.5 times; reduces 1.5 times
Mechanical control of ear sensitivity is regulated
by what?
tensor tympani and stapedius muscles; Contraction reduces sound transmission by 20 db; Ossicle joints could otherwise separate causing distortion of the sound
What is the attenuation reflex?
tensor tympani and stapedius muscles contract reflexively at loud sounds to protect the auditory
apparatus; delay of 50-100 msec
The basilar membrane dies what toward the apex?
widens
What is the helicotrema?
hole at the apex of the basilar membrane, connects the scala vestibuli and scala tympani
Why does the basilar membrane holding the hair cells vibrates easily at sound frequencies?
partly-coiling of cochlea; mainly- membrane structure varying width along length; stiffness of membrane decreases from base to apex;
The tectorial membrane has what function? characteristics?
filter of auditory system; holds tips of hairs, very flexible attachment, considerable mass, bends freely w/ slow movements, very stiff w/ fast movements (at sound frequencies); mechanical arrangement provides magnification of hair movement ->increases sensitivity
Bending of the stereocilia in cochlea is produced by what?
upward motion of the basilar membrane
Transduction by Hair Cells is acheived how?
hair tip toward tallest, cap over ion channel lifts, K+ into hair cell ->depolarization (endolymph high K+.); activates voltage-gated Ca2+ channels, Ca2+ triggers release of NT-> activates spiral ganglion fibers
Outer hair cells respond to sound with what?
receptor potential & change in length, Depol.-> motor proteins (prestin) contract-> cell shrinks in length->may augment basilar-memb. motion-> cochlear amplifier
Coding of sound intensity is done in what two interrelated ways?
Rate: intensity increases-> discharge rate of individual hair cell afferents increases; Recruitment: intensity increases, additional receptors get recruited. Not all
receptors have the same threshold.
What is Place theory of pitch coding?
hair cell measures energy in narrow band of frequencies; vibration pattern of basilar memb.& tonotopic arrang. of hair cells along membrane sharpens response of hair, arrang. provides CNS w/ frequency spectrum of sound
What is characteristic frequency?
An auditory neuron is most responsive to one frequency
What is Tonotopy?
systematic organization within auditory structure based on characteristic frequency; basilar membrane, auditory nerve, and cochlear nucleus
What is duplex theory of sound localization?
Localization of sound in horizontal plane; relies on Interaural time delay in short sound; continuous sound needs interaural intensity difference
Localization of sound in the vertical plane is based on reflection from where?
pinna
The vestibular sensory organs are the primary
organs of what?
equilibrium; transduce forces associated with head acceleration and gravity into a biological signal
The vestibular apparatus in humans serves what three major functions?
perception of orientation, posture, eye movemnets
The vestibular apparatus is what?
labyrinth of fluid filled canals and cavities in the temporal bone; associated with the cochlea.
Angular accelerations are detected by what?
3 semicircular canals, horizontal, superior & posterior
What is the ampulla? ampullary crest?
swelling on each semicircular canal; contains sensory epithelia
Sensory epithelium of vestibular system consists of what?
vestibular hair cells-> w/ cilia embedded in cupula
The canals/cavities in vestibular labyrinth are surrounded by the what? and contain?
fluid, perilymph; the fluid, endolymph
What are the properties of endolymph?
high K+, low Na+; formed by stria vascularis; found in scala media; similar to cytoplasm; potential of +80 mV.
What are the properties of perilymph?
high Na+, low K+; similar to CSF, communicates w/ CSF; in scala tympani & scala vestibule; similar to most ECF in body (0 mV).
What are the characteristics of vestiburlar hair cells?
stereocilia on apical surface-gives the hair cell a morphological axis of polarity; have a kinocilium.
The membranous labyrinth contains what?
auditory structures (cochlear duct), vestibular structures (utricle, saccule and semicircular ducts).
Vestibular afferents fire how? why?
tonically (sustained)- some cells firing persists indefinitely, info about sustained stimulation (gravity) phasically (short bursts) some cells adapt to continued
stimulation-> info about abrupt changes in bodily
accelerations
Vestibular efferents send information from where to where? Why?
brainstem back to hair cells; Stimulation decreases excitability of some hair cells (IPSP); Activation of some efferent fibers may increase excitability of some hair cells
When the stereocilia are bent toward the kinocilium what happens?
conductance of apical membrane increases for cations,
depolarization-> more transmitter is released
When the stereocilia are bent away from the kinocilium what happens?
hair cell is hyperpolarized; less transmitter is released.
When patterns of motion are such that the endolymph
moves with respect to the wall of the canals there will be what?
excitation in the member of a pair of canals on one side of the head and inhibition on the other side
Rotation of the body to the left will cause bending of the
cilia in the left horizontal canal toward what? Causing?
utricle =excitation; horizontal canal on the right side will be inhibited as its cilia are bent away from the utricle
How do the superior and posterior canals pair as they work?
superior canal on one side and posterior canal on the
other side work as a pair
Linear accelerations or head tilt are detected by what?
two otolith organs;
The utricle is connected to what?
all semicircular canals
The saccule is connected to what?
cochlea
Sensory epithelia within otolith organs are called what?
macula utriculi and macula sacculi
The otolithic membrane is what?
gelatinous mass containing otoconia, stones of calcium carbonate crystals (calcite).
what is the function of the otoconia?
increase the specific gravity of the otolithic membrane to about twice that of the endolymph; direction of bending cilia depends on orientation of resultant acceleration force
What is the characteristic of the orientation of the vestibular hair cells?
hair cells of utricular macula do not all have the same orientation with respect to kinocilia. may be bent even though the head is maintained stationary.
Vestibulo-ocular reflexes do what?
compensate head movement; head moves, eyes are kept still; Visual cues not necessary
Vestibular nystagmus does what?
resets eye position during sustained rotation of the head.
Otolith reflexes do what? What are they?
compensate for linear motion and head deviations relative to gravity; Translational vestibulo-ocular reflex and Ocular counter-rolling response
Translational vestibulo-ocular reflex does what?
compensates linear head movement; input from otoliths; Graded modification of eye movement-> focus on near objects versus distant objects as one is moving in a linear direction as in a moving car.
Ocular counter-rolling response does what?
compensates for head tilt in vertical; input from otoliths; head tilts out of vertical position, otolith organs estimate deviation from vertical and initiate counter-rolling response of eyes to compensate.
The optokinetic system supplements what?
vestibuloocular reflexes; makes up for Habituation and Insensitivity to slow head movements
Habituation is what?
reduction in responses by semicircular canals with prolonged rotation
Insensitivity to slow head movements results from what?
Slow rotation of head won’t move endolymph;
The optokinetic reflex works how?
as eyes move fixed objects seem to move opposite direction as head; drives eyes in direction of image motion; complements vestibulo-ocular reflex; responds to very slow visual image motion, can take over as vestibular signal decays
Utricle and saccule maculae detect what?
linear acceleration
Meniere’s disease is what? cause?
idiopathicendolymphatic hydrops; disorder of semicircular canals and cochlea, recurrent attacks of dizziness, tinnitus (ringing in
the ear) distorted hearing; unknown cause; appears attacks ensue from poor drainage of endolymph
