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Neuroscience > Auditory System > Flashcards

Auditory System Flashcards

1
Q

Hair cells

A

. Polarized epithelial cells
. Apical end specialized for reception and translation of mechanical energy into receptor currents
. Basal end specialized for transmission of info to the CNS via synaptic contacts w/ primary afferent neuron (housed into spinal ganglion)

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2
Q

Cochlea

A

. Part fo bony labyrinth

. Bony tube that winds spirally 23/4 turns around a modiolus (central pillar of bone)

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3
Q

Cochlear duct

A

. Part of membranous labyrinth
. Enter cochlea and is attached at edge of the 2 sides of the cochlea
. Divides cochlea into 2 long spiral chambers (Scala vestibuli above duct and scala tympani below duct)
. Scala vestibule and tympani communicate w/ each other at apex of modiolus via helictrema (small opening) and are both filled w/ perilymph
. Duct is filled w/ endolymph

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4
Q

Roof of cochlear duct

A

Vestibular (Reissner’s) membrane

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5
Q

Lateral wall of cochlear duct

A

. Spiral ligament
. Thickening of endosteum that lines cochlea
. Upper part of ligament is stria vascularis (vascularized epithelium that produces endolymph)
.

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6
Q

Floor of cochlear duct

A

. Basilar membrane that stretched from spiral ligament to osseous spiral lamina

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7
Q

Osseous spiral lamina

A

. Bony plate that winds around modiolus like threads of a screw
. Composed of 2 bony plates w/ n. Fibers in between
. Periosteum of upper surface forms an elevation (spiral limbus)

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8
Q

Tectorial membrane

A

. Thin, jelly-like membrane that arises from spiral limbus and overlies hair cells of organ of Corti

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9
Q

Organ of corti lies on ____

A

Basilar membrane

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10
Q

Organ of corti

A

. Complex epithelial structure consisting of neuroepithelial hair cells and supporting cells
. Hair cells arranged in rows: inner form single row, outer hairs for 3 rows
. Free surfaces of hair cells covered w/ sterocilia but no kinocilium
. Kinocilium embedded in tectorial membrane
. Base of each hair cell is contacted by afferent and efferent n. Endings

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11
Q

Spiral ganglion

A

. Located w/in modiolus of cochlea
. Contains 30,000 bipolar neurons
. 90% innervate hair cells w/ 1 fiber innervating 1 inner hair cell
. Each hair cell receives 10 fibers
. Inner cells are tuned to a specific tone
. 10% innervate outer hair cells w/ 1 fiber innervating many outer hair cells
. Outer hair cells receive olivocochlear synapses and function in fine-tuning aural input

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12
Q

Cochlear n. And nuclei

A

. Central process of spiral ganglion cells form cochlear n.
. Primary afferent fibers making up cochlear n. Bifurcate prior to termination in cochlear nuclei
. 1 collateral terminated in ventral cochlear nucleus
. Other collateral bifurcated once more to terminate in ventral cochlear nucleus and dorsal cochlear nucleus
. Yield 3 branches from each primary afferent fiber

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13
Q

Mechanical transduction through ear

A

. Airborne sound waves strike tympanic membrane which vibrates in response
. Vibrations transmitted across tympanic cavity via 3 bony ossicles
. Foot plate of stapes moves to and from oval window, transmitting vibration to fluid-filled inner ear
. Pressure from compression of perilymph is released via round window

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14
Q

How pressure waves get from perilymph to endolymph

A

. Pressure waves in perilymph result from oscillations of foot plate of stapes
. Pressure waves enter scala vestibuli and via helicotrema are transmitted to scala tympani
. Pressure waves transmitted through endolymph of cochlear duct makes basilar membrane vibrate

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15
Q

Characteristics of basilar membrane

A

. Narrow and taut near base of cochlea Vibrates preferentially to sounds of high pitch
. Membrane is wide and floppy neat apex of cochlea and vibrates preferentially to low pitch sounds
. Continuous resonance spectrum exists between 2 sides of membrane

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16
Q

Interactions between basilar membrane and hair cells

A

. Oscillations of basilar membrane alter the conformation between hair cell stereocilia and tectorial membrane
. Deformation of hair cells causes alteration of the pattern oof discharge in contacting afferent fibers
. APs generated in activated spiral ganglion cells and are propagated along central processes of bipolar neurons (cochlear n.) as it exits modiolus passing through internal acoustic meatus w/ vestibular component of CN VIII and enters brainstem at pontocerebellar angle

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17
Q

Dorsal and ventral cochlear nuclei

A

. Located dorsal and lat. to inf. Cerebellar peduncle

. Nuclei organized tonotopically

18
Q

Acoustic striae

A

. Fibers in 3 striae cross midline to enter contralat.
. Axons from dorsal cochlear nucleus form dorsal acoustic stria and ascend to form lat. lemniscus
. Axons from post. Portion ventral cochlear nucleus form intermediate acoustic stria, main branch projects to lat. lemniscus and collaterals project bilat. To sup. Olivary complexes
. Axons from ant. Portion of ventral cochlear nucleus form trapezoid body (ventral acoustic stria) and is largest of 3 striae, collaterals project bilat. To sup. Olivary complex

19
Q

Superior olivary complex in auditory system

A

. In caudal pons
. Consists of med. and lat. sup. Olivary nucleus and nucleus of trapezoid body
. 1st point in auditory pathway that input from both sides converges
. Cells sensitive to differences in time of arrival of auditory stimuli from both ears
. Function to localize sound in space but auditory cortex still necessary to interpret input
. Send axons bilaterally to lat. lemnisci

20
Q

Lateral lemniscus

A

. Receives secondary fibers from contralat. Cochlear nuclei via acoustic striae, and tertiary fibers from ipsilat and contralat. Sup. Olivary complex
. In lat. pons, fibers either enter nucleus of lat. lemniscus, enter RF to become part of reticular activating system (RAS), or enter inf. Colliculus

21
Q

Nucleus of lateral lemniscus

A

. Communicate w/ one another via a commissure

. Send axons to ipsilat. Inf. Colliculus

22
Q

Inf. Colliculus in auditory system

A

. Located in caudal midbrain
. Receives afferents from ipsilat lat. lemniscus, bilateral sup. Olivary nuclei, and contralat. Cochlear nuclei
. Sends fibers to opposite inf. Colliculus via commissure of inf. Colliculus and to ipsilat. Med. geniculate nucleus of thalamus via brachium of inf. Colliculus

23
Q

Medial geniculate nucleus (MGN)

A

. Located in caudal and ventral thalamus

. Axons project to ipsilat. Primary auditory cortex via sublenticular part of internal capsule

24
Q

Primary auditory cortex

A

. Located deep w/in lat. fissure
. Also called transverse temporal gyrus of Heschl (area 41,42)
. Cells show tonotopic organization

25
Q

Auditory assoc. cortex

A

. Post. 2/3 of the sup. Temporal gyrus (part of area 42, area 22)
. In dominant hemisphere
. Largely synonymous w/ Wernicke’s area

26
Q

Descending auditory pathways

A

. Olivocochlear bundle arises from nuclei close to sup. Olivary complex
. Axons leave brainstem in vestibular division of CN VIII, crossing into cochlear division in internal acoustic meatus
. Axons terminate on hair cells in organ of Corti or presynpatically on afferent fibers
. Pre and postsynaptic inhibition is used to inhibit all hair cells except those in the region of max. Basilar displacement
. Called auditory sharpening: results in dec. background noise

27
Q

Conduction deafness

A

. Vibrations do not reach oval window
. Hear better via bone conduction than normal route of air conduction
. Causes: otosclerosis (fixation of foot plate of stapes from abnormal growth of annular ligament), otitis media, excess cerumen (ear wax) in external auditory canal

28
Q

Sensoryneural deafness

A

. Due to disease of cochlea, cochlear division of CN VIII, or cochlear nuclei in medulla
. Causes: prolonged exposure to loud noise, med side effects, acoustic neuroma (Schwann cells grow too much in space of pontocerebellar angle impeding n. Transmission), BM, rubella, syphilis, Ménière’s disease

29
Q

Anacusis

A

Absent hearing

30
Q

Hypacusis

A

. Reduction in hearing

31
Q

Presbycusis

A

. Hearing loss assoc. w/ aging
. Most common cause of hearing loss
. Gradual bilateral loss w/ high-frequency tones lost first

32
Q

Ipsilateral hearing loss

A

. Caused by damage to cochlear division of CN VIII or to cochlear nuclei

33
Q

Lesions of primary auditory cortex

A

. Affect ability to localize sounds in space

. Due to commissures connecting both sides of cortices, unilateral lesion is difficult to recognize clinically

34
Q

Air conduction screening

A

. Hearing by air conduction requires intact outer, middle, and inner ear structures
. Damage to any of these could result in hearing loss via air conduction

35
Q

Bone conduction screening

A

. Hearing via bone conduction only requires intact inner ear structures
. Sensorineural deficit indicated when hearing loss is measured by bone conduction

36
Q

Unilateral conduction deafness

A

. Patient does not hear sound when tuning fork is next to ear

37
Q

Unilateral sensorineural deafness

A

. Patient hears the sounds somewhat better when tuning fork is next to ear than on mastoid process

38
Q

Weber test

A

. Normal: sound come inside patient’s head
. Unilateral conduction: sounds louder in abnormal ear
. Unilateral sensorineural: sounds louder in normal ear

39
Q

Cochlear implant

A

. Partial resorption of hearing from cartilage or complete hair cell loss
. Consists of microphone to detect sound, electronic processor that transform sound waves into code of electrical stimuli
. Array of stimulating electrodes in cochlea inserted through round window into scala tympani where it lies close to peripheral axons of primary auditory neurons
. Electrodes positioned to stimulated n. Fibers

40
Q

Success of cochlear implant depends on ____

A

. Number of surviving primary auditory neurons
. Orientation of electrodes w/ respect to neurons
. Coding scheme of processor used

Neuroscience (31 decks)

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