Physiology Of Inner Ear Flashcards
What is the structural difference between the basilar membrane at the BASE vs the APEX of the cochlea?
BASE is stiffer, prefers higher frequencies
APEX is wider, floppy. Prefers low frequencies
- Basilar membrane becomes progressively less stiff towards APEX
- physical characteristics dictate exactly where incoming frequencies are represented on the basilar membrane
What is TONOTOPICITY?
Systematic distribution of frequency representation along the basilar membrane
- high frequencies at BASE (move rapidly)
- low frequencies at APEX (move slow)
How many Outer Hair Cells and Inner Hair Cells are there in the human cochlea? Stereocilia per hair cell?
OHC- 3 rows (12,500 hairs) Tubular
20/100 stereocilia (W shaped)
OHC- 1 row (3,500 hairs)
Flashed
60 stereocilia (shallow crescent shape)
How do OVAL and ROUND windows work together?
Reciprocally.
How does the stapes footplate influence basilar membrane movement via the traveling wave?
Peak movement at particular location based on tonotopicity.
Traveling wave peak
What is the relationship between inner and outer hair cell stereocilia and the tectorial membrane at REST?
Tallest row of stereocilia for OHC are resting with movement of shearing action.
When the basilar membrane is not moving, the stereocilia is also at rest.
The tips of OHC stereocilia are embedded in the underside of the tectorial membrane, while the tips of IHC are not touching the tectorial membrane
Explain basilar membrane movement and it’s relationship to the shearing action of the tectorial membrane, and its influence on hair cell stereocilia
As the basilar membrane moves UP, the tectorial membrane will shear the tips of the stereocilia AWAY from Modiolus. This causes an excitatory response in the hair cell and causes it to depolarize
What is the purpose of SIDE links?
Stereocilia move together
Move as a unit
Provides strength
Attach laterally and frontally
What is the theoretical role of TIP links?
Open potassium channels with shearing action in exciting direction
Attach from row to row
What is the proposed role of OHC, what is hair cell motility?
How might this behavior influence IHC?
Sharpen response because we have to send discrete information to the brain.
OHC to contract on their own is a source of sharpening the frequency representation first initiated by the traveling wave.
INFLUENCING IHC to depolarize, because they send main message to the brain.
Components of VIII cranial nerve
Internal auditory meatus is 10mm
~ nerve extends 17-19mm beyond internal auditory canal, attaches to the brain stem at a juncture called Cerebellopontine Angle.
Cochlear portion: travels from spiral ganglion to organ of corti to modiolus, joining vestibular portion as it enters Internal Auditory Meatus
Vestibular portion: aka SCARPAS ganglion travels from sensory Cells of all vestibular organs and joins cochlear portion of VIII
What are Bipolar Cells?
Afferent nerve fibers
Myelinated
Have both peripheral and central axon. The dendrite conducts action potentials, which move across the cell body and propagates along the axon
What are the differences between Type I and Type II spiral ganglion Cells ?
TYPE I- myelinated, large, 90%, attach to IHC, “many -to-one”
Lateral efferent nerve contacts on afferent nerve directly, not IHC. (Pink/blue picture)
TYPE II- unmyelinated, small, 10%, connect to OHC directly, “one-to-many”
Afferent nerves
Sensory
30,000 fibers
Takes sensory information from PNS to CNS
Enters cochlea through the habenula perforata
Efferent nerves
Motor
1,200 fibers (travel from brainstem to OHC, few to IHC)
Provide motor innervation from CNS to PNS
