Physiology of the Auditory and Vestibular System Flashcards
What are the physical properties of the basilar membrane at its base near the oval and round windows?
- narrow
- stiff
What are the physical properties of the basilar membrane at its apex near the helicotrema?
- wide
- flexible
Where do high frequency sounds create the greatest deflection along the basilar membrane?
-near the base where it’s narrow and stiff
Where do low frequency sounds create the greatest deflection along the basilar membrane?
-near the apex where it’s wide and flexible
Define tonotopy.
- distinct locations along the basilar membrane within the inner ear interpret distinct frequencies
- analogous to somatotopy of the motor and sensorimotor cortices
Explain the relationship b/w the hair cells, the tectorial membrane and the basilar membrane.
- stereocilia of the hair cells are embedded in the tectorial membrane
- body of the hair cells rest on the basilar membrane
List the steps that lead to the cochlear N. being stimulated due to upward displacement of the basilar membrane.
- lateral displacement of sterocilia (tips stretch)
- TRPA1 channels open (mechanotransduction)
- K+ influx and depolarization
- voltage-gated Ca channels open
- glutamate-filled vesicles released
What happens if the basilar membrane is displaced downward?
-hyperpolarization
What does the stria vascularis create?
-endolymph
Endolymph has a high concentration of what ion?
-potassium
How is the potassium transported from the capillaries into the endolymph?
- stria vascularis extends cytoplasmic processes around the capillaries to take in the released potassium
- “intraepithelial plexus” exists that carries this out
What does the high endocochlear concentration of K+ aid in creating?
- Blood-Labyrinth Barrier
- positive ions are driven down their concentration gradient into the hair cells
What is a main way for drugs to get into the hair cells?
-Blood-Labyrinth Barrier
If a drug disrupts the function of the stria vascularis, how would that lead to hearing loss?
- less K+ in the endolymph means less K+ that can flow into the hair cells to depolarize them
- less Ca channels open, which means less glutamate-filled vesicles are released (cochlear N. not stimulated)
What is the purpose of the outer hair cells?
-amplify sound and cause mvmt of basilar membrane
How many rows of outer hair cells are there?
-three
What do outer hair cells synapse with?
- peripheral sensory afferent from spiral ganglion
- terminals from efferent neurons
What is the purpose of inner hair cells?
-primary source of auditory information
How many layers of inner hair cells are there?
-one
What do inner hair cells synapse with?
- peripheral terminal of primary afferent sensory
- efferent neurons for activity modulation
What are otoacoustic emissions?
- when outer hair cells move retrograde toward oval window and moves the ossicles, causing displacement of the tympanic membrane from the interior
- aka … the ear itself produces a sound
What are otoacoustic emissions useful for?
-newborn hearing screening
How do olivocochlear efferents protect the cochlea during intense sounds?
- reduce electromotility of outer hair cells, thus decreasing basilar membrane motion
- in turn, this reduces responses of inner hair cells and auditory nerve fibers
How muscles does the middle ear use to protect the cochlea by attenuating intense sounds?
- tensor tympani M. (connected to malleus and the tympanic membrane) (innervated by CN V)
- stapedius M. (connected to stapes) (innervated by CN VII
