Physiology of Auditory and Vestibular Systems

Question 1

Basilar membrane structure

Answer 1

Narrow and stiff near oval/round windows - detects high frequency sounds
Wide and flexible near helicotrema - defects low frequency sounds

Question 2

TRPA1 channels

Answer 2

Connected to stereocilia and are opened when the stereocilia are displaced
Mechanotransduction channels- can open within 50us
Do no require receptor potentials
Allows K+ influx

Question 3

Endolymph

Answer 3

Potassium rich fluid filling the cochlear duct and membranous labyrinth
Bathes the apical end of the hair cells
Found in scala media, produced by stria vascularis

Question 4

Perilymph

Answer 4

Potassium POOR

Found in scala vestibuli and tympani

Question 5

Downward vs upward displacement of basilar membrane

Answer 5

Downward causes hyperpolarization, while upward causes lateral displacement and depolarization

Question 6

Ototoxic drug effect on stria vascularis

Answer 6

Blood labyrinth barrier is one of main sites of drug entry to access the inner hair cells
Any substance that disrupts function of the stria vascularis will diminish the endocochlear potential and impact hearing

Question 7

Inner vs outer hair cells

Answer 7

Inner hair cells are primary source of auditory information and synapse with the peripheral terminal of a primary afferent sensory neuron
Outer hair cells are primary cells that amplify sound waves that results in movement of the basilar membrane
-outer cells are contractile which help them boost the mechanical vibrations of the basilar membrane

Question 8

Otoacoustic emissions

Answer 8

Originate in the superior olivary complex
Known as olivocochlear efferents
Medial olivary complex neurons innervate outer hair cells
Lateral olivary complex neurons innervate inner hair cells
OAE testing measures the presence or absence of sound waves generated by the cochlear outer hair cells in response to sound stimuli

Question 9

Olivocochlear efferents

Answer 9

Reduces electromotility of outer hair cells
Decreases basilar membrane motion
Reduces responses of inner hair cells and auditory nerve fibers

Question 10

Medial ear efferents

Answer 10

Tensor tympani to the malleus and the tympanic membrane - attenuates sound
Stapedius to the stapes - attenuates sound
Act at low frequencies, may prevent damage

Question 11

Autonomic efferents in ear

Answer 11

Arise from CN VIII
Sympathetic adrenergic fibers
Regulates vascular tone in blood supply to the cochlea

Question 12

Dorsal vs ventral cochlear nuclei

Answer 12

DCN- integrates acoustic information with somatosensory information
VCN- begins processing the temporal and spectral features of the sound

Question 13

Medial superior and lateral superior olivary complex MSO/LSO

Answer 13

MSO- generates a map of interaural time differences to help localization of sound
LSO- generates a map of interaural intensity differences to help localize the source of a sound

Question 14

Inferior colliculus

Answer 14

Suppresses information related to echoes, which would interfere with localization and arrives at a final estimation of localization of sound along the horizon
Receives info about time and intensity differences to help create precise origin of sound location

Question 15

Medial geniculate nucleus

Answer 15

Helps process features of speech inflections

Precise info regarding intensity, frequency and binaural properties are integrated and relayed onward

Question 16

Primary auditory cortex

Answer 16

Essential in conscious perception of sound

Higher order processing of sound

Question 17

Secondary auditory association cortex

Answer 17

Brocas, wernickes etc..

Respond to more complex sounds like music, identifying/naming a sound, and speech

Question 18

Utricle vs saccule

Answer 18

Utricle detects linear acceleration forward and backward

Saccule detects linear acceleration up and down