Hearing

Question 1

Mechanism of cochlear implants

Answer 1

• Pass multiple electrodes into the scala tympani

- Determines which electrodes should be activated in accordance with its analysis of the sound waves being presented

Question 2

Amplitude of a sound wave

Answer 2

• Represents the magnitude of the pressure change

- Greater amplitude means a greater physical magnitude of the sound (in decibels)

Question 3

Decibel

Answer 3

20*log(test pressure/reference pressure)

Question 4

Compensation for loss of energy (and consequently dB) at the oval window

Answer 4

• 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

Question 5

Tympanometry

Answer 5

• Clinical technique that measures the impedance of the middle ear to sound
• Conductive hearing loss: more sound reflected than in the normal middle ear

Question 6

Frequency analysis

Answer 6

• 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

Question 7

Steps of analyzing sound

Answer 7

• 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.

Question 8

Distance a travelling wave will progress

Answer 8

• 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

Question 9

Auditory receptor cells

Answer 9

• 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

Question 10

Organ of corti

Answer 10

• 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

Question 11

Bending toward the kinocilium

Answer 11

-Depolarization

Question 12

Bending away from kinocilium

Answer 12

-Hyperpolarization

Question 13

Cochlear nuclei

Answer 13

• 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

Question 14

Primary auditory cortex

Answer 14

• Transverse temporal gyrus

- Buried in the sylvian fissure

Question 15

Organization of the primary auditory cortex

Answer 15

• 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

Question 16

Vestibular system

Answer 16

• 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

Question 17

Ampulla

Answer 17

• 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

Question 18

Sacculus and utricle

Answer 18

• Vestibular organ
• Striola separates hair cells with opposite polarity
• Concerned with more linear movements

Question 19

Polarization of vestibular hair cells

Answer 19

• Utricle oriented horizontally
• Sacculus oriented vertically
• Allows for continuous representation of all body movement directions

Question 20

Otolithic membrane

Answer 20

• 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

Question 21

Response of vestibular hair cells and vestibular nerve

Answer 21

• 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

Question 22

Three degrees of rotation

Answer 22

• Yaw: around z axis
• Pitch: around y axis
• Roll: around x axis

Question 23

Teamwork of the paired canals

Answer 23

• 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

Question 24

Vestibular occular reflex

Answer 24

• 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)

Question 25

Pathological nystagmus

Answer 25

• 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