Physiology of the Auditory and Vestibular Systems Flashcards
Describe the basilar membrane near the oval and round windows versus near the helicotrema?
Oval/Round Windows: narrow and stiff
Helicotrema: wider and more flexible
What do high frequency sounds cause at the basilar membrane?
Greater deflection of the basilar membrane where it is narrow and stiff
What do lower frequency sounds cause at the basilar membrane?
Greater deflection of the basilar membrane where it is loose and flexible
How is the frequency of sound (pitch) coded?
Coded by where along the basilar membrane there is the greatest deflection
Define the auditory system
Detects sound and uses acoustic cues to identify and locate sound sources in the environment
Define sound
Oscillations of air pressure that vary rapidly with time
Define amplitude
Sound pressure (intensity) specified by a scale of sound pressure level (SPL) in decibels (dB)
Define frequency
Number of oscillations of air pressure per second (Hz)
What is tonotopy? What does this apply to?
Applies to the inner ear, with distinct locations interpreting discrete frequencies
What does the vibration of the basilar membrane create?
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
When does depolarization of the cell occur?
When cation channels open at the apex of the stereocilia
How are stereocilia connected and what do these connections do?
Connected to each other via tip links that transmit force to an elastic gating spring, which in turn, opens the TRPA1 channels
How fast can hair cells respond to a stimulus?
50 microseconds
What is endolymph?
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
What is perilymph?
Potassium-poor fluid that bathes the basal end of the cochlear hair cells; found in scala vestibuli and scala tympani
Similar to extracellular fluid
After the hair cells have depolarized, what happens?
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
What are inner hair cells?
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
What are outer hair cells?
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
What are OAE’s?
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
What are olivocochlear efferents?
Reduce electromotility of outer hair cells; decreases basilar membrane motion; reduce responses of inner hair cells and auditory nerve fibers
What are media ear efferents?
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
What are autonomic efferents?
Arise from CN VIII; sympathetic adrenergic fibers; regulates vascular tone in blood supply to cochlea
What is the function of the dorsal cochlear nuclei?
Integrates the acoustic information with somatosensory information
What is the function of the ventral cochlear nuclei?
Begins processing the temporal and spectral features of the sound
What is the function of the medial/lateral superior olivary nucleus?
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
What is the function of the inferior colliculus?
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
What is the function of the medial geniculate nucleus?
Processes features of speech inflections; precise information regarding intensity, frequency, and binaural properties of sound are integrated and relayed onward;
Tonotopic map is maintained
What is the function of the primary auditory cortex (A1)?
Essential in conscious perception of sound; higher order processing of sound (loudness, modulations in volume, rate of frequency modulation)
Tonotopic map is maintained
What is the function of the secondary auditory association cortex (A2)?
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
What is the function of the anterior semicircular canal?
Rotation in the vertical plane forwards maximally activates anterior semicircular canal (falling forward)
What is the function of the horizontal semicircular canal?
Rotation in the horizontal plane is best detected by the horizontal semicircular canal (spinning/twirling)
What is the function of the posterior semicircular canal?
Rotation in the vertical plane backwards maximally activates the posterior semicircular canal (falling backward)
What is the function of the utricle?
Detects linear acceleration forward and backward (running)
What is the function of the saccule?
Detects linear acceleration up and down (jumping)
