764 research outputs found
Dual contribution to amplification in the mammalian inner ear
The inner ear achieves a wide dynamic range of responsiveness by mechanically
amplifying weak sounds. The enormous mechanical gain reported for the mammalian
cochlea, which exceeds a factor of 4,000, poses a challenge for theory. Here we
show how such a large gain can result from an interaction between amplification
by low-gain hair bundles and a pressure wave: hair bundles can amplify both
their displacement per locally applied pressure and the pressure wave itself. A
recently proposed ratchet mechanism, in which hair-bundle forces do not feed
back on the pressure wave, delineates the two effects. Our analytical
calculations with a WKB approximation agree with numerical solutions.Comment: 4 pages, 4 figure
Coherent motion of stereocilia assures the concerted gating of hair-cell transduction channels
The hair cell's mechanoreceptive organelle, the hair bundle, is highly
sensitive because its transduction channels open over a very narrow range of
displacements. The synchronous gating of transduction channels also underlies
the active hair-bundle motility that amplifies and tunes responsiveness. The
extent to which the gating of independent transduction channels is coordinated
depends on how tightly individual stereocilia are constrained to move as a
unit. Using dual-beam interferometry in the bullfrog's sacculus, we found that
thermal movements of stereocilia located as far apart as a bundle's opposite
edges display high coherence and negligible phase lag. Because the mechanical
degrees of freedom of stereocilia are strongly constrained, a force applied
anywhere in the hair bundle deflects the structure as a unit. This feature
assures the concerted gating of transduction channels that maximizes the
sensitivity of mechanoelectrical transduction and enhances the hair bundle's
capacity to amplify its inputs.Comment: 24 pages, including 6 figures, published in 200
Essential nonlinearities in hearing
Our hearing organ, the cochlea, evidently poises itself at a Hopf bifurcation
to maximize tuning and amplification. We show that in this condition several
effects are expected to be generic: compression of the dynamic range,
infinitely shrap tuning at zero input, and generation of combination tones.
These effects are "essentially" nonlinear in that they become more marked the
smaller the forcing: there is no audible sound soft enough not to evoke them.
All the well-documented nonlinear aspects of hearing therefore appear to be
consequences of the same underlying mechanism.Comment: 4 pages, 3 figure
Chain Community Pharmacists\u27 Willingness, Attitudes, and Barriers in Providing Self-Care Medication and Supplement Recommendations
BACKGROUND: Pharmacists are commonly called on as the first resource for patients when selecting an appropriate self-care medication or supplement. This study examines pharmacists’ over-the-counter (OTC) recommendations in the chain community pharmacy setting in the United States. OBJECTIVES: The objective of the study was to assess chain community pharmacists’ willingness and attitudes to provide self-care recommendations to patients and to identify chain community pharmacists’ barriers to making OTC medication and supplement recommendations. METHODS: An anonymous survey was created to identify pharmacists’ attitudes and their willingness to perform these recommendations. The questionnaire included specific questions to identify barriers that exist to making OTC recommendations. The survey was distributed by fax and email to 527 pharmacists in the Mid-South regional district of a U.S. grocery chain pharmacy. Descriptive statistics were used to identify demographic trends and display results. RESULTS: Pharmacists are overwhelmingly willing to provide OTC recommendations (100%) and see it as an important part of community practice (99%). The greatest barriers were time/prescription volume (94%) and staffing demands (78%). The greatest need for education was in the areas of eye/ear care and vitamins/herbal products. CONCLUSIONS: The results affirmed pharmacists’ willingness and overall positive attitude to providing OTC medication counseling in the community pharmacy setting. The research uniquely identified barriers that pharmacists experience when attempting to make OTC recommendations. This information can be used not only for the implementation of patient care services targeting self-care needs but also in the application of general community pharmacy practice
Optimizing the vertebrate vestibular semicircular canal: could we balance any better?
The fluid-filled semicircular canals (SCCs) of the vestibular system are used
by all vertebrates to sense angular rotation. Despite masses spanning seven
decades, all mammalian SCCs are nearly the same size. We propose that the SCC
represents a sensory organ that evolution has `optimally designed'. Four
geometric parameters are used to characterize the SCC, and `building materials'
of given physical properties are assumed. Identifying physical and
physiological constraints on SCC operation, we find that the most sensitive SCC
has dimensions consistent with available data.Comment: 4 pages, 3 figure
Structural and functional characterization of the CAP domain of pathogen-related yeast 1 (Pry1) protein
The production, crystal structure, and functional characterization of the C-terminal cysteine-rich secretory protein/antigen 5/pathogenesis related-1 (CAP) domain of pathogen-related yeast protein-1 (Pry1) from Saccharomyces cerevisiae is presented. The CAP domain of Pry1 (Pry1CAP) is functional in vivo as its expression restores cholesterol export to yeast mutants lacking endogenous Pry1 and Pry2. Recombinant Pry1CAP forms dimers in solution, is sufficient for in vitro cholesterol binding, and has comparable binding properties as full-length Pry1. Two crystal structures of Pry1CAP are reported, one with Mg2+ coordinated to the conserved CAP tetrad (His208, Glu215, Glu233 and His250) in spacegroup I41 and the other without divalent cations in spacegroup P6122. The latter structure contains four 1,4-dioxane molecules from the crystallization solution, one of which sits in the cholesterol binding site. Both structures reveal that the divalent cation and cholesterol binding sites are connected upon dimerization, providing a structural basis for the observed Mg2+-dependent sterol binding by Pry1
Information Flow through a Chaotic Channel: Prediction and Postdiction at Finite Resolution
We reconsider the persistence of information under the dynamics of the
logistic map in order to discuss communication through a nonlinear channel
where the sender can set the initial state of the system with finite
resolution, and the recipient measures it with the same accuracy. We separate
out the contributions of global phase space shrinkage and local phase space
contraction and expansion to the uncertainty in predicting and postdicting the
state of the system. Thus, we determine how the amplification parameter, the
time lag, and the resolution influence the possibility for communication. A
novel representation for real numbers is introduced that allows for a
visualization of the flow of information between scales.Comment: 14 pages, 13 figure
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