Nervous System: Kretzer Auditory System

Front 1

4 functions of kinocilium during fetal development

Back 1

- create axis of bilateral symmetry
- establish height of hair bundles
- dictates (via height) the diameter of the stereocilia whose actin inserts into cuticular plate
- resp for short/fat to tall/skinny gradient that exists from base to apex of cochlea (unique phenomenon of outer HCs)

Front 2

Why do babies hear higher pitches better at birth?

Back 2

bc at birth, kinocilium involutes starting from base to apex. myelination of second order neurons occurs first in those second order neurons carrying information about high pitched frequencies from base of cochlea. thus, baby hears better at higher pitched sounds

Front 3

Compare the single row of inner HCs vs the 3 rows of outer HCs in the organ of Corti.

Back 3

They both have phalangeal cells and pillar cells adjacent to them.

Front 4

Contrast the single row of inner HCs vs the 3 rows of outer HCs in the organ of Corti.

Back 4

- inner phalangeal cells totally surround inner hair cells but outer phalangeal cells have space in between bc there is somatic electromotility in the outer HCs
- only inner HCs are arranged in stepladder wall-like configuration (for efficient depolarization by endolymph jet)
- only outer HCs have stereocilia bundle that inserts into undersurface of tectorial membrane; only outer HCs are capable of electrosomatic motility with the depression of basilar membrane
- only inner HCs depolarize and release glutamate into secondary afferent neurons in the spiral ganglion
- only outer HCs have unique W shaped hair bundle with short/fat to tall/skinny change from base to apex of cochlea
- outer HC don't have secondary afferent neurons at the base of outer hair cells. however there are lots of inhibitory efferents of the olivocochlear blundle on basal surface of the outer HCs.

Front 5

The basilar membrane is suspended between the _________ and the ______________.

Back 5

tympanic lip of the osseous spiral lamina; spiral ligament

Front 6

the basilar membrane is VASCULAR/AVASCULAR.

Back 6

avascular

Front 7

define reticular lamina

Back 7

single, unified functional unit made up of cuticular plates linked by adherent junctions that tilt with the depression of the outer pillar cells

Front 8

3 boundaries of scala media witih its k-rich endolymph

Back 8

- Reissner's membrane
- Stria vascularis
- reticular lamina

Front 9

2 ways that endolymph jet occurs

Back 9

- depolarization causes outer HCs to shrink and W shaped stereocilia bundle catches endolymph
- as outer HC shorten, they narrow the space between the reticular lamina and the tectorial membrane to further create more of the endolymph jet. Due to the action of the outer hair cells, the traveling wave is converted into a very narrow focused envelope with a unique point of maximal defection along the tonotopic map which is nothing but place coding.

Front 10

path of endolymph jet

Back 10

• Under the tectorial membrane
• Over the inner hair cells
• Around the inner spiral tunnel
• Bangs into the inner hair cell stereocilia causing depolarization

Front 11

What are the causes of otoacoustic emissions?

Back 11

the highly sensitized microphone in the external auditory canal can hear specific sounds generated by:
• Synovial joints between the malleus, incus, and stapes
• Pulsation of the foot process of the stapes in the oval window
• inner/outer pillar cells as outer pillar cells drops
• Reticular lamina dropping
• Somatic electromotility shortening of the outer hair cells with depolarization
• Movement of the endolymph jet

Front 12

How does the afferent auditory central pathway calculate the localization of sound in space?

Back 12

1) bilateral cross-talk at multiple synapses (superior olivary nucleus, nuc of lateral lemniscus, inferior colliculus, corpus callosum)
2) timing and intensity differences b/w ears
3) sound shadow produced by pinna

Front 13

Explain why any lesion distal to cochlear nucleus has no impact on hearing but only on localization.

Back 13

• Because of 40/60 bilaterality of the ascending auditory afferent pathway, any given central lesion does not produce a hearing deficit but only a very annoying inability to localize sound from the contralateral side.

Front 14

State the pathway from cochleus to the brain

Back 14

cochleus, cochlear nucleus, superior olivary nucleus, nucleus of lateral lemniscus (pons), inferior colliculus (midbrain), medial geniculate nucleus of thalamus, Brodman's 41 (in temporal lobe via auditory radiations in the PLIC)

Front 15

Where is there commissural cross talk and where is there calossal cross talk?

Back 15

commisurral:
- between nucleus of lateral lemniscus
- commissure of inferior colliculus

calossal:
- between both Brodmann areas 41

Front 16

What are the causes of unilateral deafness?

Back 16

• Problems in the middle ear
• Hair cells/tectorial membrane within the organ of Corti
• Spiral ganglion
• Cochlear nucleus
basically any lesion peripheral to the cochlear nucleus. one example is acoustic neuroma; if bilateral, think Neurofibromatosis 2

Front 17

What does early demyelinating plaque in MS cause?

Back 17

• Internuclear ophthalmoplegia
• Sudden vision loss in one eye due to a demyelinating plaque in the optic nerve
• Inability to localize sound in space due to a demyelinating plaque at some site along the afferent auditory pathway

Front 18

What do the 5th,6,7,8th order neurons for each Hertz do in the auditory system?

Back 18

they eventually synapse in a unique auditory dominance column in Brodmann 41 tuned to one specific Hz

Front 19

List the pyramidal outputs of a givenn auditory dominance column in A1(Brodmann's 41) which is tuned to a specific Hz.

Back 19

o From each auditory dominance column in Brodmann 41
• Some pyramidal outputs become inhibitory efferents to the MGN back down along the auditory radiations.
• Other pyramidal neurons become inhibitory efferents to the inferior colliculus (back down the auditory radiations and the brachium of the inferior colliculus).
o From both the medial geniculate nucleus and the inferior colliculus, inhibitory efferents descend in the lateral lemniscus and bombard inhibition on the superior olivary nucleus, tonotopically
o The newest data indicate that there are no inhibitory stops in the nucleus of the lateral lemniscus
o The olivocochlear bundle leaves the superior olivary nucleus, crosses the midline in the trapezoid body, avoids the cochlear nucleus, and passes out the spiral ganglion and impacts on the three rows of outer hair cells causing them via hyperpolarization to elongate via somatic electromovements. This elongation tightens the basilar membrane so that it cannot vibrate at the exact place of the hertz along the tonotopic map that you consciously do NOT want to hear.

Front 20

What is detected in the noninvasive audioevoked brainstem response (ABR)?

Back 20

Use the audio-evoked brainstem response (ABR) before newborn released from the hospital
o Place external electrode patch on skin along brainstem (totally noninvasive and done with a portable machine) so you record wave form of activity in three nuclei
• Cochlear nucleus
• Superior olivary nucleus
• Inferior colliculus
o Give a train of clicks in each ear (100 clicks per second at 3000 Hz at 60dB) and detect waveform of activity along the brain stem

Front 21

What are causes of congenital (bilateral) deafness?

Back 21

-hair cells are dead
-some spiral bipolar neurons of CN8 and the afferent auditory pathway are intact

Front 22

Explain the very strong inhibitory efferents in the auditory system. Compare this with the scarce inhibitory efferents of the vestibular system.

Back 22

The strong inhibitory efferents in the auditory system come from the auditory dominance columns that send inhibitory signals to both the inferior colliculus and directly to the medial geniculate to dampen down specific hertz's by ultimately causing hyperpolarization and decreased somatic electromotility of outer HCs in the organ of Corti at specific hertz range. this is very strong in the sense that the inhibition really works to block out certain unwanted pitches.

the scarce inhibitory efferents in the vestibular system, in contrast, are pisspoor and do not really constitute a major effect upon the system at all.

Front 23

How does a cochlear implant work?

Back 23

Wear a speech processor in your pocket, so speech is broken down maximally into 17 hertzes, somewhere in the consonant range. So then you can understand speech better. Breaks down into hertzes into a transmitter. Then they have carved out in temporal bone where receiver is and the electrodes are fed up the round window through scala tympani (in fluid) and now it literally sends electrical stimulation to stimulate depolarization in the spiral ganglia.
- only pt with bilateral deafness can get cochlear implant and requires intact CN8 pathway from 2nd order bipolar cells to brain.

Front 24

Compare cochlear implant with Auditory Brainstem Implant (ABI).

Back 24

ABI- Used only when both spiral ganglions (CN8) are removed due to neurofibromatosis type II. Implant is placed in recess of 4th ventricle over tonotopic map of cochlear nucleus. These 21 electrodes sink directly into cochlear nucleus. She can differentiate b/w dog barking, husband speaking, etc. but still not perfect hearing…

cochlear implant- spiral ganglions still intact so electrodes feed into scala tympani through round window to send electrical stimulation to stimulate depolarization in the spiral ganglia

Front 25

Reasons for deafness within the organ of Corti

Back 25

• Death of hair cells by rubella, CMV, aminoglycosides, cisplatin
• Mutated three proteins in the tectorial membrane
• Mutated five repair and maintenance enzymes of the hair bundle
• Labile cilia syndromes (kinocilium falls apart before the hair bundle is formed along the gradient of short/fat to tall/skin)
• Acoustic trauma
• Episodic elevations of endolymph pressure as in Meniere’s disease (death of hair cells from apex to base)
• Death of bipolar cells in spiral ganglion due to obstruction of internal auditory artery or proliferation of Schwann cells