Physiology of the Auditory and Vestibular Systems

Question 1

Describe the basilar membrane near the oval and round windows versus near the helicotrema?

Answer 1

Oval/Round Windows: narrow and stiff

Helicotrema: wider and more flexible

Question 2

What do high frequency sounds cause at the basilar membrane?

Answer 2

Greater deflection of the basilar membrane where it is narrow and stiff

Question 3

What do lower frequency sounds cause at the basilar membrane?

Answer 3

Greater deflection of the basilar membrane where it is loose and flexible

Question 4

How is the frequency of sound (pitch) coded?

Answer 4

Coded by where along the basilar membrane there is the greatest deflection

Question 5

Define the auditory system

Answer 5

Detects sound and uses acoustic cues to identify and locate sound sources in the environment

Question 6

Define sound

Answer 6

Oscillations of air pressure that vary rapidly with time

Question 7

Define amplitude

Answer 7

Sound pressure (intensity) specified by a scale of sound pressure level (SPL) in decibels (dB)

Question 8

Define frequency

Answer 8

Number of oscillations of air pressure per second (Hz)

Question 9

What is tonotopy? What does this apply to?

Answer 9

Applies to the inner ear, with distinct locations interpreting discrete frequencies

Question 10

What does the vibration of the basilar membrane create?

Answer 10

Creates a pressure differential, which results in a shearing force against the stationary tectorial membrane, causing the stereocilia of the outer hair cells to be displaced in that plane

Question 11

When does depolarization of the cell occur?

Answer 11

When cation channels open at the apex of the stereocilia

Question 12

How are stereocilia connected and what do these connections do?

Answer 12

Connected to each other via tip links that transmit force to an elastic gating spring, which in turn, opens the TRPA1 channels

Question 13

How fast can hair cells respond to a stimulus?

Answer 13

50 microseconds

Question 14

What is endolymph?

Answer 14

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

Similar to intracellular fluid

Question 15

What is perilymph?

Answer 15

Potassium-poor fluid that bathes the basal end of the cochlear hair cells; found in scala vestibuli and scala tympani

Similar to extracellular fluid

Question 16

After the hair cells have depolarized, what happens?

Answer 16

Calcium channels at the base of the cells open, calcium flows in, which causes neurotransmitter-filled vesicles to fuse with the basilar membrane and release the neurotransmitter glutamate into the synaptic cleft; the afferent cochlear nerve fibers are thus stimulated and transmit this signal to the CNS

Question 17

What are inner hair cells?

Answer 17

Primary source of auditory information; arranged in a single layer; synapse with the peripheral terminal of a primary afferent sensory neuron; an efferent neuron also modulates activity as well

Question 18

What are outer hair cells?

Answer 18

Primary cells that amplify sound waves that results in the movement of the basilar membrane; cells are also contractile, making them a specialized type of epithelial cell; 3 rows of outer hair cells that form a synapse with sensory afferent peripheral terminals from the spiral ganglion, as well as with terminals from efferent neurons

Question 19

What are OAE’s?

Answer 19

Sounds that the ear itself produces; originate in the superior olivary complex, known as olivocochlear efferents; medial olivary complex neurons innervate outer hair cells while lateral olivary complex neurons innervate inner hair cells

Measured in infants to assess function of inner and middle ears

Question 20

What are olivocochlear efferents?

Answer 20

Reduce electromotility of outer hair cells; decreases basilar membrane motion; reduce responses of inner hair cells and auditory nerve fibers

Question 21

What are media ear efferents?

Answer 21

Tensor tympani to the malleus and tympanic membrane, which attenuates sound; or stapedius to the stapes (from CN VII), which attenuates sound; may prevent damage; implicated in tinnitus

Question 22

What are autonomic efferents?

Answer 22

Arise from CN VIII; sympathetic adrenergic fibers; regulates vascular tone in blood supply to cochlea

Question 23

What is the function of the dorsal cochlear nuclei?

Answer 23

Integrates the acoustic information with somatosensory information

Question 24

What is the function of the ventral cochlear nuclei?

Answer 24

Begins processing the temporal and spectral features of the sound

Question 25

What is the function of the medial/lateral superior olivary nucleus?

Answer 25

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 *Receive glutamergic (excitatory) input and a tonotopic map is maintained*

Question 26

What is the function of the inferior colliculus?

Answer 26

Suppresses information related to echoes, which would interfere with localization and arrives at a final estimation of localization of sound along the horizon; information about time and intensity differences converge into the IC to help create a precise origin of sound location along the horizon *Tonotopic map is maintained in IC*

Question 27

What is the function of the medial geniculate nucleus?

Answer 27

Processes features of speech inflections; precise information regarding intensity, frequency, and binaural properties of sound are integrated and relayed onward; *Tonotopic map is maintained*

Question 28

What is the function of the primary auditory cortex (A1)?

Answer 28

Essential in conscious perception of sound; higher order processing of sound (loudness, modulations in volume, rate of frequency modulation) *Tonotopic map is maintained*

Question 29

What is the function of the secondary auditory association cortex (A2)?

Answer 29

Composed of multiple areas (Broca's, Wernicke's); less specifically organized in the tonotopic arrangement than the primary auditory cortex; thought to respond to more complex sounds (music), identifying (naming) a sound, and speech

Question 30

What is the function of the anterior semicircular canal?

Answer 30

Rotation in the vertical plane forwards maximally activates anterior semicircular canal (falling forward)

Question 31

What is the function of the horizontal semicircular canal?

Answer 31

Rotation in the horizontal plane is best detected by the horizontal semicircular canal (spinning/twirling)

Question 32

What is the function of the posterior semicircular canal?

Answer 32

Rotation in the vertical plane backwards maximally activates the posterior semicircular canal (falling backward)

Question 33

What is the function of the utricle?

Answer 33

Detects linear acceleration forward and backward (running)

Question 34

What is the function of the saccule?

Answer 34

Detects linear acceleration up and down (jumping)