Auditory and Vestibular System Flashcards
tympanic membrane connects with this bone
Malleus
Ossicular chain consists of these three bones
malleus, incus, and stapes
stabes vibrates against
the oval window
Fluid inside the cochlea is incompressible, which travels through scala vestibuli and scala tympani, and gets let out at this place
the round window
The basilar membrane sits in the middle of?
The cochlea
What are the best frequencies for each end of the basilar membrane?
basal end: high frequency
apical end: low frequency
This end of the membrane is at the base of the cochlea near the stapes
the basal end (high frequency)
Sitting on the basilar membrane is the
organ of corti
Fluid movement results in these three effects
Shearing, deflection, depolarization
how many rows are there of inner and outer hair cells?
A single row of inner hair cells (3,000), 3-5 outer (12,000)
membrane potential of inner hair cells
-45 mV
Perilymph contained within _______, (high/low K+), and membrane potential
Scala tympani, low K+, 0 mV
Endolymph contained within ____, (high/low K+), membrane potential
Scale media, High K+, 80 mV
Depolarization of hair cells (move towards the tallest) causes an influx/outflux of K+ into the cell
Influx (K+ moves from endolymph, which has a higher K+ concentration). This is a weird exception to what normally happens during depolarization.
Depolarization of the hair cell causes these channels to open allowing ions to come (in/out) of cell
Calcium channels open, calcium enters, causes release of transmitter
Deflection of hair cell produces what type of potentials
graded potentials (away from resting potential of -45 to -60 mV)
Depolarization is caused from an (upward/downward) movement of basilar membrane
Upward
Hyperpolarization is caused from an (upward/downward) movement of basilar membrane
Downward
The membrane sitting on top of the hair cells
tectorial membrane
30,000 afferent fibers are coming in, what is the percentage that synapse on inner hair cells?
90-95%
ratio of fibers synapsing with inner hair cells
20 fibers to 1 single inner hair cell
enormous amount of redundancy
Ratio of fibers synapsing on outer hair cell
1 single fiber innervating ~10 outer hair cells
Efferent fibers coming from ___ synapse on hair cells producing an (excitatory/inhibitory) response
Superior olive, inhibitory response (modulate response)
The type of neurons innervating hair cells
biopolar neurons
As kHZ increases, move towards (apical/basal) end
basal (recall that kHz is BIG–2 kHz would be considered high frequency)
How to identify inner and outer hair cells from a photo:
Inner hair cells: flat hair bundles
Outer hair cells: triangular, v-shaped hair bundles
Bult of information into auditory system comes from
inner hair cells-primary afferent receptors
2,000 efferent fibers synapse largely on outer hair cells. What is their job?
Adjust level of the system to change the threshold of your hearing
Low frequency would travel down and reach its peak in which region
Apical region
High frequency wave would reach maximum vibration at what end of the membrane?
at the base (basal)
These hair cells are responsible for
tuning the membrane, enables sharp tuning
Characteristic frequency
tip of the tuning curve, sharpest point of tuning, outer hair cell role
Phase-locking
auditory nerve is firing in lock step with the frequency of sound coming in
Phase locking is a (low/high) frequency phenomena
Low frequency
Cut off for phase locking
nothing above 1,000 Hz, works for anything about
A click contains broad range of frequencies. Auditory nerve fibers in lock step up tunil a higher frequency at which point this dissolves. This is measured using what?
PST (post-stimulus time) histograms
Explain “cochlea sings”
The whole cochlea is active, it is called the cochlear amplification and has energy.
This part of ear is important for vertical localization, allowing us to differentiate sounds coming from above, below, front and behind
pinna
Works as a funnel for pressure variations of sound
ear canal
The greater the amplitude, the (greater/lesser) distance the tympanic membrane moves
greater
Most sensitive region of tympanic membrane
2-3 kHz, where much of human speech is
No single auditory nerve codes the entire 120 decibel range. How can system respond to such a dynamic wide range?
high spontaneous rate fibers- many fibers, saturate quickly after certain threshold
low spontaneous rate fibers-few fibers, threshold beings at higher sound level, takes a while to saturate
frequency analyzer
peripheral auditory system
designer to determine what and where a sound is
central auditory system
temporal coding
phase locking, “where” it is relies on this
Each fiber first synapses and bifurcates here
cochlear nucleus
Bifurcation of fibers at cochlear nucleus innevate caudal and rostral branch, and end up in these two areas
PVCN/DCN = dorsal cochlear nucleus AVCN = anterior ventrical of cochlear nucleus
end-bulbs of Held
auditoiry nerve terminals, sepcial and secure synapses, maintain tight timing and locking to stimulus (sound coming in
End-bulbs of Held securely synapse on this type of cell
a single bushy cell (getting convergence of many auditory nerve fibers on a single bushy cell, supports highly synchronized timing)
Cochlear nuclei cell
bushy cell
What happens after a bushy cell integrates signals
if can get enough agreement, it will fire an action potential
The signal moves up from cochlear nucleus to this next region / level of processing
Superior olive, mid pons
First site of crossing of inputs of ears, serves binaural processing
Superior olive
Major binaural cues (2)
- Interaural temporal disparities (ITD)
2. Interaural intensitive disparities (IID)
ITD
Timing differences across the ear, predominant cue at low frequencies (phase locking is low frequency phenomena)
IID
When sound over to one side, generally more intense at the ear on that side. Depends on frequency of sound, predominant cue is at high frequencies (because at low frequencies, it travels around the head/head shadow, so there isn’t much difference)
Coincidence detection
explains how the pattern of auditory nerve and trapezoid fibers fire. Bushy cell requires the summation of several events, needs some agreement
axon of bushy fiber
trapezoid body fiber
AVCN sends its signals through trapzeoid body and ends up here, containing what type of cells?
Contralateral medial superior olive (MSO); contains EE (excitatory-excitatory) cells
What type of detection is present in the MSO?
Binaural coincidence detection
Characteristic delay
each cell in MSO (each coincidence detector) has a time delay it likes to receive
MSO cell will not fire an AP without
coincident input-needs agreement from both ears
How does the system inside the brain compensate for delays outside the brain?
Arrangement of cells in MSO such that there are different lengths of axonal inputs, axon is shorter ipsilateral, requires precise timing
MSO projects (ipsilaterally/contralaterally), and arrives here
Ipsilaterally, inferior colliculus (and beyond)
Location of inferior colliculus
caudal midbrain
Processing of Interaural time disparities (ITD) sends inputs here
Medial Superior Olive
Processing of Interaural intensitive disparities (IID) sends inputs here
Lateral Superior Olive
High frequency and IID signals in cochlear nucleus make two connections. Where are they, and are they excitatory or inhibitory?
Ipsilateral LSO - Excitatory
Contralateral LSO- Inhibitory
The Lateral superior olive projects ipsilaterally (excitatory/inhibitory) and contralaterally (excitatory/inhibitory) to the inferior colliculus
Ipsilateral IC-inhibitory
Contralateral IC- excitatory
Afferent activity in the central auditory system generally proceeds through the following areas. Which is THIRD in the sequence?
A. cochlear nucleus B. inferior colliculus C. medial geniculate D. superior olivary nucleus E. superior temporal gyrus
B. All auditory afferents synapse in this midbrain structure.
Auditory afferents travel through the midbrain in the
A. medial lemniscus B. lateral lemniscus C. medial longitudinal fasciculus D. trapezoid body E. sublenticular portion of the internal capsule
B.
The vestibular system serves these three primary functions = equilibrial triad
- Head position
- Posture/balance
- Stabilization of visual images (fixation point of eyes when the head moves
thus interacts with visual-motor and proprioceptive systems
Relative to the cochlea, the vestibular apparatus is (anterior/posterior)
posterior position
the space between the bony and membranous labyrinth? filled with?
perilymph, CSF
membranous labyrinth is also filled with this fluid
endolymph
high in potassium ions and resembles intracellular fluid
endolymph
two cavernous structures, collectively referred to as
utricle and saccule = otolithic organs
The receptor regions of the semicircular canals reside in a dilated portion called?
Ampulla
The receptor area for the utricle and saccule reside in a sheet like area called?
macula
This hair cell type is akin to the inner hair cells of the cochlea, and is the primary sensory transducer
Type I
This type of hair cell closely corresponds to the outer hair of cochlea
Type II
Each of the hair cells has 100 of these modified microvilli and a single one of these modified cilia
Steriocilia, kinocilium
Movements of the steriocilia towards the kinocilium produce (hyperpolarization/depolarization) of the hair cell and (inhibitory/excitatory) discharges in the afferent fiber
depolarization, excitatory
What establishes the hair cell’s polarity?
Kinocilium (but not involved in the actual generator mechanisms)
This provides a shearing force on the embedded stereocilia during head movement
otoconia or otolith (calcium carbonate crystals)
The hair cells are organized as functional paris along this line
striola (so within a pair, when one hair cell is excited, the other is inhibited)
There is a (high/low) level of discharge at resting levels
high (40 spikes/sec when head it in normal position, 0 degrees tilt)
For the sensory epithelium of the semicirucular canals, the force for bending hair cells is provided by what pushing against what during what type of movement?
Endolymph pushing against the cupula during angular rotation
Cupula
gelatinous material in the semicircular canals that embed the stereocilia
Function pair organization seen in the macula is not present within the cupula. Why not?
All the hair cells are oriented the same way
Function pair oragnization for semicircular canals is brought about by the relationship between semicircular canal pairs where?
on right and left side
Once angular acceleration has stopped, what happens to the force on the cupula?
It is no longer present because moves at same rate as head (which is good or we’d feel sick all the time!)
Afferents innervating the hair cells have their cell bodies where?
Scarpa’s ganglion
Scarpa’s ganglion is divided into a superior and inferior division. Which cell bodies go where?
Superior vestibular ganglion- afferents from the superior and horizontal canals and utricle
Inferior vestibular ganglion- afferents from posterior canal and saccule
The axons of the ganglion cells form the vestibular part of VIII and enter the upper medulla and ___ of the cerebellum
inferior peduncle
Upon entering the brain, the primary afferents bifurcate into short ascending and descending fibers before synapsing in the _______
vestibular nuclei
How many vestibular nuclei are they, and what part of the medulla do they occupy?
4 (each has a distinct set of inputs and outputs), large part of the medulla beneath the floor of the fourth ventricle
The medial longitudinal fasiculus (MLF) is comprised of crossed and uncrossed fibers from the lateral, superior, and medial vestibular nuclei, which ascend and innervate?
Extraocular nuclei (oculomotor, trochelar, and abducens)
What is the function of the Medial longitudinal fasiculus pathway?
Control conjugate eye movement in coordination with head movements to maintain visual fixation
This reflex serves to stabilize visual images during head movements
vestibulo-oculomotor reflexes (VORs)
As head rotates to left, the endolymph pushes against the cupula and causes the hair cells in the left horizontal canal to (hyper/depolarize)
depolarize, increase firing in their afferents
As head rotates to left, increased afferents make excitatory synapse onto neurons in the (ipsilateral/contralateral) ________
ipsilateral medial vestibular nuclei (left side)
The axons from the medial vestibular nucleus cross the midline and make excitatory synapses onto neurons in the contralateral _______, which in turn activate the _______
abducens nucleus, lateral rectus of right eye
Some of the axons from the right abducens nucleus cross the midline and travel with the left ____ to make excitatory synapses onto neurons in the left _____ muscles, which activates the ____ muscle of the left eye
Medial longitudinal fasiculus (MLF), occulomotor nucleus, medial rectus
Non comatose patients: cold water evokes fast phase of nystagmus, causing the eyes to move in the (same/opposite) direction to the ear that was stimulated
Opposite direction
COWS (cold-opposite, warm-same)
(CSWO for comatose)
two phases of nystagmus
slow phase-slow conjugate eye movement in the direction opposite to the rotational direction
fast phase- quick eye movement to reset in direction the rotation occurs
Comatose patients do not display which phase
fast phase (thoguht to be a cerebral reflex, while slow phase involves the vestibulo-ocular pathway)
When using a cold caloric test in right ear, a patient with a bilateral MLF lesion displays the following:
Appropriate nystagmus in the right eye, left eye remains stationary (axons from the abducents to the opposite occulomotor nucleus that travel in the MLF are lesioned)
When use cold caloric text in right ear, a patient with a low brain stem lesion displays the following:
Both are remain stationary (occurs because either the abducens and/or the vestibular nuclei are destroyed
