Lecture 2: Physiology of Auditory and Vestibular Systems Flashcards
(41 cards)
What is the auditory system?
Detects sound and uses acoustic cues to identify and locate sound sources in the environment
- Sound: oscillations of air pressure that can vary
What is amplitude and frequency?
- Amplitude: Sound pressure (intensity) measured by decibels
- Frequency: numer of oscillations of pair pressure per second measured by Hz
Where do higher frequency sounds displace the basilar membrane?
Near oval window where basilar membrane is narrow and stiff
Ex: 20,000 Hz
Where do low frequency sounds displace the basilar membrane?
Near helicotrema (tip of cochlea) where the membrane is wide and flexible
Ex: 10,000 Hz
What is the ion distribution for endolymph found in scala media?
High [K+}
Low [Na+]
Bathes apical end of hair cells
What is the ion distribution for perilymph found in scala vestibuli and tympani?
Low [K+]
High [Na+]
Bathes basal end of hair cells
What CN transmits central axons from the primary auditory neurons of the spiral ganglion to the brainstem?
CN VIII (vestibulocochlear)
What type of receptors are hair cells?
Mechanoreceptors
- Have afferent and efferent input
- Not neuronal
- Converts mechanical signals to electrical signals
- Neural synapses on basal side
What motion of the hair cell stereocilia causes depolarization?
Deflection towards the Kinocilium
- Rapid influx of K+ causes depolarization
- Calcium channels open, releasing NT to basilar membrane
What motion of the hair cell stereocilia causes hyperpolarization?
Deflection away from the kinocilium
What neurotransmitter is released by the hair cells?
Glutamate
What channel on the stereocilia allows entry of K+?
TRPA1
What part of the cochlea is the stria vascularis located in?
What is its function?
Scala media
Maintains electrochemical properties of endolymph by pumping K+ in
What is the function of inner hair cells?
Primary source of auditory information
- Arranged in a single layer.
- Synapse with the peripheral terminal of a primary afferent sensory neuron
What is the function of the three rows of outer hair cells?
- Act as amplifier
- Boost mechanical vibrations of basilar membrane
- Otoacoustic emissions: low-level sound emitted by the cochlea either spontaneously or evoked by an auditory stimulus
- Originate in the superior olivary complex
What is the importance of otoacoustic emissions?
Check function of inner and middle ears in newborn hearing screen
What type of hair cells both send afferent neurons and receive efferent neurons?
Outer hair cells
What is the function of the superior olivary nucleus?
Determines the direction from which a sound originates
What neurons innervate outer hair cells?
Medial olivary complex neurons
What neurons innervate inner hair cells?
Lateral olivary complex neurons
What is the function of olivocochlear efferents?
- Shifting response to higher sound levels
- Decrease adaptation
- Reduces the response to noise
- Protect hair cells from damage to intense sounds
What parts of the middle ear send efferents to the auditory system? From what cranial nerves?
- Tensor Tympani to malleus (CN V)
- Stapedius to stapes (CN VII)
What is the main function of middle ear efferents?
Prevent damage: decrease transmission of sound (act at low frequencies)
How does sound reach and leave the hair cells?
- Sound hits stapes, causing it to move.
- Scala vestibuli pressure falls below scala tympani pressure.
- Basilar membrane bows upward.
- Organ of corti shears toward hinge of tectorial membrane.
- Hair bundles of outer hair cells tilt toward their longer stereovilli.
- Transduction channels open in outer hair cells.
- Depolarization contracts the motor protein prestin.
- Contraction of outer hair cells accentuates upward movement of the basilar membrane (makes waves in endolymph).
- Endolymph waves beneath the tectorial membrane.
- Inner hair cells bend toward the longer stereovilli.
- Transduction channels open in the inner hair cells.
- Depolarization opens voltage gated Ca2+ channels.
- Synaptic vesicles fuse, releasing glutamate.
