scholarly journals Frequency selectivity of synaptic exocytosis in frog saccular hair cells

2006 ◽  
Vol 103 (8) ◽  
pp. 2898-2903 ◽  
Author(s):  
M. A. Rutherford ◽  
W. M. Roberts
Keyword(s):  
Hair Cells ◽  
Frequency Selectivity ◽  
Synaptic Exocytosis

scholarly journals Static length changes of cochlear outer hair cells can tune low-frequency hearing

2017 ◽  
Author(s):  
Nikola Ciganović ◽  
Rebecca L. Warren ◽  
Batu Keçeli ◽  
Stefan Jacob ◽  
Anders Fridberger ◽  
...  
Keyword(s):  
Inner Ear ◽  
Hair Cells ◽  
Organ Of Corti ◽  
Outer Hair Cells ◽  
Frequency Selectivity ◽  
Apical Region ◽  
Low Frequencies ◽  
Inner Hair Cells ◽  
Length Changes ◽  
The Brain

AbstractThe cochlea not only transduces sound-induced vibration into neural spikes, it also amplifies weak sound to boost its detection. Actuators of this active process are sensory outer hair cells in the organ of Corti, whereas the inner hair cells transduce the resulting motion into electric signals that propagate via the auditory nerve to the brain. However, how the outer hair cells modulate the stimulus to the inner hair cells remains unclear. Here, we combine theoretical modeling and experimental measurements near the cochlear apex to study the way in which length changes of the outer hair cells deform the organ of Corti. We develop a geometry-based kinematic model of the apical organ of Corti that reproduces salient, yet counter-intuitive features of the organ’s motion. Our analysis further uncovers a mechanism by which a static length change of the outer hair cells can sensitively tune the signal transmitted to the sensory inner hair cells. When the outer hair cells are in an elongated state, stimulation of inner hair cells is largely inhibited, whereas outer hair cell contraction leads to a substantial enhancement of sound-evoked motion near the hair bundles. This novel mechanism for regulating the sensitivity of the hearing organ applies to the low frequencies that are most important for the perception of speech and music. We suggest that the proposed mechanism might underlie frequency discrimination at low auditory frequencies, as well as our ability to selectively attend auditory signals in noisy surroundings.Author summaryOuter hair cells are highly specialized force producers inside the inner ear: they can change length when stimulated electrically. However, how exactly this electromotile effect contributes to the astonishing sensitivity and frequency selectivity of the inner ear has remained unclear. Here we show for the first time that static length changes of outer hair cells can sensitively regulate how much of a sound signal is passed on to the inner hair cells that forward the signal to the brain. Our analysis holds for the apical region of the inner ear that is responsible for detecting the low frequencies that matter most in speech and music. This shows a mechanisms for how frequency-selectivity can be achieved at low frequencies. It also opens a path for the efferent neural system to regulate hearing sensitivity.

Role of inner and outer hair cells in mechanical frequency selectivity of the cochlea

1985 ◽  
Vol 18 (2) ◽  
pp. 169-175 ◽  
Author(s):  
D. Strelioff ◽  
Å. Flock ◽  
K.E. Minser
Keyword(s):  
Hair Cells ◽  
Outer Hair Cells ◽  
Frequency Selectivity

The temporal characteristics of Ca2+ entry through L-type and T-type Ca2+ channels shape exocytosis efficiency in chick auditory hair cells during development

2012 ◽  
Vol 108 (11) ◽  
pp. 3116-3123 ◽  
Author(s):  
Snezana Levic ◽  
Didier Dulon
Keyword(s):  
Hair Cells ◽  
Low Voltage ◽  
Domestic Chick ◽  
Cochlear Hair Cells ◽  
Auditory Hair Cells ◽  
Temporal Characteristics ◽  
Cochlear Development ◽  
Synaptic Exocytosis ◽  
Fast Release ◽  
Ca2 Channels

During development, synaptic exocytosis by cochlear hair cells is first initiated by patterned spontaneous Ca2+ spikes and, at the onset of hearing, by sound-driven graded depolarizing potentials. The molecular reorganization occurring in the hair cell synaptic machinery during this developmental transition still remains elusive. We characterized the changes in biophysical properties of voltage-gated Ca2+ currents and exocytosis in developing auditory hair cells of a precocial animal, the domestic chick. We found that immature chick hair cells (embryonic days 10–12) use two types of Ca2+ currents to control exocytosis: low-voltage-activating, rapidly inactivating (mibefradil sensitive) T-type Ca2+ currents and high-voltage-activating, noninactivating (nifedipine sensitive) L-type currents. Exocytosis evoked by T-type Ca2+ current displayed a fast release component (RRP) but lacked the slow sustained release component (SRP), suggesting an inefficient recruitment of distant synaptic vesicles by this transient Ca2+ current. With maturation, the participation of L-type Ca2+ currents to exocytosis largely increased, inducing a highly Ca2+ efficient recruitment of an RRP and an SRP component. Notably, L-type-driven exocytosis in immature hair cells displayed higher Ca2+ efficiency when triggered by prerecorded native action potentials than by voltage steps, whereas similar efficiency for both protocols was found in mature hair cells. This difference likely reflects a tighter coupling between release sites and Ca2+ channels in mature hair cells. Overall, our results suggest that the temporal characteristics of Ca2+ entry through T-type and L-type Ca2+ channels greatly influence synaptic release by hair cells during cochlear development.

scholarly journals Modeling the resonant release of synaptic transmitter by hair cells as an example of biological oscillators with cooperative steps

2010 ◽  
Vol 107 (5) ◽  
pp. 2019-2024 ◽  
Author(s):  
Daniel Andor-Ardó ◽  
A. J. Hudspeth ◽  
Marcelo O. Magnasco ◽  
Oreste Piro
Keyword(s):  
Synaptic Transmission ◽  
Hair Cells ◽  
Release Site ◽  
Nerve Fibers ◽  
Frequency Selectivity ◽  
Cyclic Process ◽  
Step Cycle ◽  
Biological Oscillators ◽  
Afferent Nerve Fibers ◽  
Complex Eigenvalues

The initial synapses of the auditory system, which connect hair cells to afferent nerve fibers, display two unusual features. First, synaptic transmission occurs in a multiquantal fashion: the contents of multiple synaptic vesicles are discharged simultaneously. Second, synaptic transmission may be tuned to specific frequencies of stimulation. We developed a minimal theoretical model to explore the possibility that hair-cell synapses achieve both multiquantal release and frequency selectivity through a cooperative mechanism for the exocytotic release of neurotransmitter. We first characterized vesicle release as a four-step cycle at each release site, then generalized the result to an arbitrary number of steps. The cyclic process itself induces some degree of resonance, and may display a stable, underdamped fixed point of the release dynamics associated with a pair of complex eigenvalues. Cooperativity greatly enhances the frequency selectivity by moving the eigenvalues toward the imaginary axis; spontaneously oscillatory release can arise beyond a Hopf bifurcation. These phenomena occur both in the macroscopic limit, when the number of release sites involved is very large, and in the more realistic stochastic regime, when only a limited number of release sites participate at each synapse. It is thus possible to connect multiquantal release with frequency selectivity through the mechanism of cooperativity.

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