Hearing Flashcards
1
Q
Mechanism of cochlear implants
A
- Pass multiple electrodes into the scala tympani
- Determines which electrodes should be activated in accordance with its analysis of the sound waves being presented
2
Q
Amplitude of a sound wave
A
- Represents the magnitude of the pressure change
- Greater amplitude means a greater physical magnitude of the sound (in decibels)
3
Q
Decibel
A
20*log(test pressure/reference pressure)
4
Q
Compensation for loss of energy (and consequently dB) at the oval window
A
- Smaller area–20 fold increase in pressure
- Lever action of ossicular chain–exceeds force at tympanic membrane by 1.3
- Overall increase in pressure of a factor of 26
- 3dB reflects back
5
Q
Tympanometry
A
- Clinical technique that measures the impedance of the middle ear to sound
- Conductive hearing loss: more sound reflected than in the normal middle ear
6
Q
Frequency analysis
A
- Determined by the impact on the basilar membrane
- Basilar membrane increases in width and decreases in stiffness from base to apex
- Increase in phase lag from base to apex
7
Q
Steps of analyzing sound
A
- Basilar membrane is coupled to traveling wave, through the fluid media surrounding it
- As stapes moves into the oval window a volume of scala vestibuli is compressed
- Round window bulges out to compensate
- Restoring force brings the membrane back up to a neutral position
- When stapes moves out an upward bulge is produced which, following the downward bulge produces a full traveling wave.
8
Q
Distance a travelling wave will progress
A
- Greater frequency will travel less distance along the basilar membrane
- Lower frequency will travel a greater distance along the basilar membrane
- Only the lowest frequencies will produce waves traveling the full length of the membrane
9
Q
Auditory receptor cells
A
- Arranged in an orderly manner along basilar membrane
- Translates a template of mechanical events into a primary neuron discharge
- Respond in proportion to the amplitude of the traveling wave at their positions along the basilar membrane
- Housed in the organ of corti
10
Q
Organ of corti
A
- Houses the auditory receptors
- Rests upon the basilar membrane
- Hair cells are lodged within the tectorial membrane at the roof of the organ of corti
- Pushing on the basilar membrane pushes the tectorial membrane up which causes a shearing action on the cilia
11
Q
Bending toward the kinocilium
A
-Depolarization
12
Q
Bending away from kinocilium
A
-Hyperpolarization
13
Q
Cochlear nuclei
A
- Operate in a parallel and hierarchical fashion
- Each 8th nerve fiber terminates within the cochlear nuclei by branching to each of its three divisions (posteroventral, anteroventral, dorsal)
- Full range of frequencies is represented in each of the three nuclei
- High frequencies dorsally and low frequencies ventrally in each nuclei
14
Q
Primary auditory cortex
A
- Transverse temporal gyrus
- Buried in the sylvian fissure
15
Q
Organization of the primary auditory cortex
A
- Neurons of similar best frequency arrayed in a strip running perpendicular to the high low tonotopic axis
- Some cells appear to be involved with patterns of pitch rather than pitch itself
16
Q
Vestibular system
A
- Output of the vestibular system is proportional to head velocity
- ie:sends signal to rotate eyes in the opposite direction of movement but with the same acceleration
17
Q
Ampulla
A
- Vestibular organ
- Located at base of semicircular canal
- Hair cells oriented in the same direction
- Detect angular direction of movement
- Contains a gelatinous membrane called the cupula
- Displaced by inertia of fluid in the canal due to angular acceleration or deceleration of the head
- Fluid (endolymph) goes in opposite direction as acceleration
- Detects rotation in the horizontal plane
18
Q
Sacculus and utricle
A
- Vestibular organ
- Striola separates hair cells with opposite polarity
- Concerned with more linear movements
19
Q
Polarization of vestibular hair cells
A
- Utricle oriented horizontally
- Sacculus oriented vertically
- Allows for continuous representation of all body movement directions
20
Q
Otolithic membrane
A
- Vestibular hair apexes of utricle and sacculus project into it
- Comprised of otoconia–calcium carbonate crystals that add mass to the membrane
- Will move in opposite direction of acceleration
21
Q
Response of vestibular hair cells and vestibular nerve
A
- Bending toward kinocilum: depolarization–>increases firing of CN8 fiber (K+ filters in which then opens Ca2+ channels)
- Bending away from kinocilium: hyperpolarization–>decrease response of CN8 fiber
22
Q
Three degrees of rotation
A
- Yaw: around z axis
- Pitch: around y axis
- Roll: around x axis
23
Q
Teamwork of the paired canals
A
- Bilateral horizontal canals work together
- Anterior canal on one side works with posterior canal on the other side
- Rotation in one direction will excite the hair cells in one canal of a pair and inhibit the other canal
- Left and right responses are summed
24
Q
Vestibular occular reflex
A
- Left rotation excited L CN8 and vestibular nuclei, inhibits the right
- L vestibular nuclei excite the R abducens nucleus which activates the right lateral rectus muscle
- Via mlf the L vestibular nuclei excites L CN3 nucleus which activates the left medial rectus muscle
- Cause the eyes to rotate right (equal and opposite direction of the rotation)
25
Q
Pathological nystagmus
A
- Resting discharge mistakenly read as true head motion
- If no activity in the L canal will perceive a right rotation
- Will see slow eye movements to the left and a quick saccade reset to the right
