Computational modeling indicates that surface pressure can be reliably conveyed to tactile receptors even amidst changes in skin mechanics

Distinct patterns in neuronal firing are observed between classes of cutaneous afferents. Such differences may be attributed to end-organ morphology, distinct ion-channel complements, and skin microstructure, among other factors. Even for just the slowly adapting type I afferent, the skin's mechanics for a particular specimen might impact the afferent's firing properties, especially given the thickness and elasticity of skin can change dramatically over just days. Here, we show computationally that the skin can reliably convey indentation magnitude, rate, and spatial geometry to the locations of tactile receptors even amid changes in skin's structure. Using finite element analysis and neural dynamics models, we considered the skin properties of six mice that span a representative cohort. Modeling the propagation of the surface stimulus to the interior of the skin demonstrated that there can be large variance in stresses and strains near the locations of tactile receptors, which can lead to large variance in static firing rate. However, variance is significantly reduced when the stimulus tip is controlled by surface pressure and compressive stress is measured near the end organs. This particular transformation affords the least variability in predicted firing rates compared with others derived from displacement, force, strain energy density, or compressive strain. Amid changing skin mechanics, stimulus control by surface pressure may be more naturalistic and optimal and underlie how animals actively explore the tactile environment.

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Computation identifies structural features that govern neuronal firing properties in slowly adapting touch receptors

eLife ◽

10.7554/elife.01488 ◽

2014 ◽

Vol 3 ◽

Cited By ~ 55

Author(s):

Daine R Lesniak ◽

Kara L Marshall ◽

Scott A Wellnitz ◽

Blair A Jenkins ◽

Yoshichika Baba ◽

...

Keyword(s):

Network Models ◽

Structural Features ◽

Neuronal Firing ◽

Type I ◽

Merkel Cells ◽

Action Potential Initiation ◽

Plausible Mechanism ◽

Firing Properties ◽

High Degree ◽

Potential Initiation

Touch is encoded by cutaneous sensory neurons with diverse morphologies and physiological outputs. How neuronal architecture influences response properties is unknown. To elucidate the origin of firing patterns in branched mechanoreceptors, we combined neuroanatomy, electrophysiology and computation to analyze mouse slowly adapting type I (SAI) afferents. These vertebrate touch receptors, which innervate Merkel cells, encode shape and texture. SAI afferents displayed a high degree of variability in touch-evoked firing and peripheral anatomy. The functional consequence of differences in anatomical architecture was tested by constructing network models representing sequential steps of mechanosensory encoding: skin displacement at touch receptors, mechanotransduction and action-potential initiation. A systematic survey of arbor configurations predicted that the arrangement of mechanotransduction sites at heminodes is a key structural feature that accounts in part for an afferent’s firing properties. These findings identify an anatomical correlate and plausible mechanism to explain the driver effect first described by Adrian and Zotterman.

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Effects of changing skin mechanics on the differential sensitivity to surface compliance by tactile afferents in the human finger pad

Journal of Neurophysiology ◽

10.1152/jn.00176.2014 ◽

2015 ◽

Vol 114 (4) ◽

pp. 2249-2257 ◽

Cited By ~ 4

Author(s):

Kathryn M. Hudson ◽

Melia Condon ◽

Rochelle Ackerley ◽

Francis McGlone ◽

Håkan Olausson ◽

...

Keyword(s):

Venous Occlusion ◽

Differential Sensitivity ◽

Type I ◽

Firing Rates ◽

Skin Mechanics ◽

Unloading Rate ◽

Low Threshold ◽

Firing Properties ◽

Human Finger ◽

Finger Pad

It is not known how changes in skin mechanics affect the responses of cutaneous mechanoreceptors in the finger pads to compression forces. We used venous occlusion to change the stiffness of the fingers and investigated whether this influenced the firing of low-threshold mechanoreceptors to surfaces of differing stiffness. Unitary recordings were made from 10 slowly adapting type I (SAI), 10 fast adapting type I (FAI) and 9 slowly adapting type II (SAII) units via tungsten microelectrodes inserted into the median nerve at the wrist. A servo-controlled stimulator applied ramp-and-hold forces (1, 2, and 4 N) at a constant loading and unloading rate (2 N/s) via a flat 2.5-cm-diameter silicone disk over the center of the finger pad. Nine silicone disks (objects), varying in compliance, were used. Venous occlusion, produced by inflating a sphygmomanometer cuff around the upper arm to 40 ± 5 mmHg, was used to induce swelling of the fingers and increase the compliance of the finger pulp. Venous occlusion had no effect on the firing rates of the SAI afferents, nor on the slopes of the relationship between mean firing rate and object compliance at each amplitude, but did significantly reduce the slopes for the FAI afferents. Although the SAII afferents possess a poor capacity to encode changes in object compliance, mean firing rates were significantly lower during venous occlusion. The finding that venous occlusion had no effect on the firing properties of SAI afferents indicates that these afferents preserve their capacity to encode changes in object compliance, despite changes in skin mechanics.

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Soil Modeling Using FEA and SPH Techniques for a Tire-Soil Interaction

Volume 8: 11th International Power Transmission and Gearing Conference; 13th International Conference on Advanced Vehicle and Tire Technologies ◽

10.1115/detc2011-47104 ◽

2011 ◽

Cited By ~ 1

Author(s):

Moustafa El-Gindy ◽

Ryan Lescoe ◽

Fredrik O¨ijer ◽

Inge Johansson ◽

Mukesh Trivedi

Keyword(s):

Surface Pressure ◽

Particle Density ◽

Plastic Material ◽

Material Model ◽

Shear Displacement ◽

Physical Models ◽

Element Analysis ◽

Elastic Plastic ◽

Vertical Loading ◽

Fea Model

In recent years, the advancement of computerized modeling has allowed for the creation of extensive pneumatic tire models. These models have been used to determine many tire properties and tire-road interaction parameters which are either prohibitively expensive or unavailable with physical models. More recently, computerized modeling has been used to explore tire-soil interactions. The new parameters created by these interactions were defined for these models, but accurate soil constitutive equations were lacking. With the previous models, the soil was simulated using Finite Element Analysis (FEA). However, the meshless modeling method of Smooth Particle Hydrodynamics (SPH) may be a viable approach to more accurately simulating large soil deformations and complex tire-soil interactions. With both the FEA and SPH soils modeled as elastic-plastic solids, simplified soil tests are conducted. First, pressure-sinkage tests are used to explore the differences in the two soil-modeling methods. From these tests, it is found that the FEA model supports a surface pressure via the tensile forces created by the stretching of the surface elements. Conversely, for the SPH model, the surface pressure is supported via the compressive forces created by the compacting of particles. Next, shear-displacement tests are conducted with the SPH soil (as this test cannot easily be performed with an FEA soil model). These shear tests show that the SPH soil behaves more like clay in initial shearing and more like sand by exhibiting increased shearing due to vertical loading. While both the pressure-sinkage and shear-displacement tests still show that a larger particle density is unnecessary for SPH soil modeling, the shear-displacement tests indicate that an elastic-plastic material model may not be the best choice.

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Differential Modulation of Synaptic Strength and Timing Regulate Synaptic Efficacy in a Motor Network

Journal of Neurophysiology ◽

10.1152/jn.00809.2010 ◽

2011 ◽

Vol 105 (1) ◽

pp. 293-304 ◽

Cited By ~ 10

Author(s):

Bruce R. Johnson ◽

Jessica M. Brown ◽

Mark D. Kvarta ◽

Jay Y. J. Lu ◽

Lauren R. Schneider ◽

...

Keyword(s):

Synaptic Input ◽

Synaptic Strength ◽

Neuronal Firing ◽

Cycle Period ◽

Cycle Frequency ◽

Pyloric Network ◽

Motor Network ◽

Pyloric Dilator ◽

Network Output ◽

Firing Properties

Neuromodulators modify network output by altering neuronal firing properties and synaptic strength at multiple sites; however, the functional importance of each site is often unclear. We determined the importance of monoamine modulation of a single synapse for regulation of network cycle frequency in the oscillatory pyloric network of the lobster. The pacemaker kernel of the pyloric network receives only one chemical synaptic feedback, an inhibitory synapse from the lateral pyloric (LP) neuron to the pyloric dilator (PD) neurons, which can limit cycle frequency. We measured the effects of dopamine (DA), octopamine (Oct), and serotonin (5HT) on the strength of the LP→PD synapse and the ability of the modified synapse to regulate pyloric cycle frequency. DA and Oct strengthened, whereas 5HT weakened, LP→PD inhibition. Surprisingly, the DA-strengthened LP→PD synapse lost its ability to slow the pyloric oscillations, whereas the 5HT-weakened LP→PD synapse gained a greater influence on the oscillations. These results are explained by monoamine modulation of factors that determine the firing phase of the LP neuron in each cycle. DA acts via multiple mechanisms to phase-advance the LP neuron into the pacemaker's refractory period, where the strengthened synapse has little effect. In contrast, 5HT phase-delays LP activity into a region of greater pacemaker sensitivity to LP synaptic input. Only Oct enhanced LP regulation of cycle period simply by enhancing LP→PD synaptic strength. These results show that modulation of the strength and timing of a synaptic input can differentially affect the synapse's efficacy in the network.

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Using the Asphalt Pavement Layer Condition Assessment Program: Case Studies

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/1860-08 ◽

2003 ◽

Vol 1860 (1) ◽

pp. 66-75 ◽

Cited By ~ 3

Author(s):

Bing Xu ◽

S. Ranji Ranjithan ◽

Y. Richard Kim

Keyword(s):

Case Studies ◽

Asphalt Pavement ◽

Compressive Strain ◽

Dynamic Effect ◽

Field Measurements ◽

Condition Assessment ◽

Base Layer ◽

Element Analysis ◽

Condition Indicators ◽

Assessment Program

The Asphalt Pavement Layer Condition Assessment Program (APLCAP) is developed in this research to help highway agencies assess layer conditions of asphalt pavements. APLCAP implements a new integrated procedure for condition assessment from falling-weight deflectometer (FWD) deflections. The main components of this procedure include screening of FWD raw deflections, predictions of condition indicators from FWD measurements, structural adjustments for the predicted condition indicators, and layer condition evaluation based on the adjusted condition indicators. This procedure was developed on the basis of dynamic nonlinear finite element analysis and calibrated using field measurements. The three case studies presented show that the APLCAP algorithms can predict the asphalt concrete modulus, pavement critical strains, and strengths of the base and subgrade quite well, but not the compressive strain in the aggregate base layer. Although the APLCAP procedure includes the complicated dynamic effect of FWD loading and nonlinear behavior of unbound materials, the time to obtain results from this procedure is insignificant and therefore suitable for real-time evaluation of pavement conditions.

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A finite element analysis of the pelvic reconstruction using fibular transplantation fixed with four different rod-screw systems after type I resection

Chinese Medical Journal ◽

10.1097/00029330-200802020-00008 ◽

2008 ◽

Vol 121 (4) ◽

pp. 321-326 ◽

Cited By ~ 13

Author(s):

Yong-wei JIA ◽

Li-ming CHENG ◽

Guang-rong YU ◽

Cheng-fei DU ◽

Zhi-yong YANG ◽

...

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Type I ◽

Pelvic Reconstruction ◽

Element Analysis

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Characteristic Membrane Potential Trajectories in Primate Sensorimotor Cortex Neurons Recorded In Vivo

Journal of Neurophysiology ◽

10.1152/jn.00024.2005 ◽

2005 ◽

Vol 94 (4) ◽

pp. 2713-2725 ◽

Cited By ~ 45

Author(s):

Daofen Chen ◽

Eberhard E. Fetz

Keyword(s):

Membrane Potential ◽

Sensorimotor Cortex ◽

High Frequency ◽

Cortical Neurons ◽

Type I ◽

Type Ii ◽

Interspike Intervals ◽

Cortical Oscillations ◽

Firing Properties

We examined the membrane potentials and firing properties of motor cortical neurons recorded intracellularly in awake, behaving primates. Three classes of neuron were distinguished by 1) the width of their spikes, 2) the shape of the afterhyperpolarization (AHP), and 3) the distribution of interspike intervals. Type I neurons had wide spikes, exhibited scoop-shaped AHPs, and fired irregularly. Type II neurons had narrower spikes, showed brief postspike afterdepolarizations before the AHP, and sometimes fired high-frequency doublets. Type III neurons had the narrowest spikes, showed a distinct post-AHP depolarization, or “rebound AHP” (rAHP), lasting nearly 30 ms, and tended to fire at 25–35 Hz. The evidence suggests that an intrinsic rAHP may confer on these neurons a tendency to fire at a preferred frequency governed by the duration of the rAHP and may contribute to a “pacemaking” role in generating cortical oscillations.

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Research on Pulley Strain of Metal Belt CVT

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.952.249 ◽

2014 ◽

Vol 952 ◽

pp. 249-252

Author(s):

Wu Zhang ◽

Wei Guo ◽

Fa Rong Kou ◽

Yi Zhi Yang

Keyword(s):

Finite Element Analysis ◽

Finite Element ◽

Analytical Method ◽

Compressive Strain ◽

Continuously Variable Transmission ◽

Transmission Ratio ◽

Element Analysis ◽

Variable Transmission

Pulley strain aggravated whole-Part abrasion, affected friction and lubricates state of metal belt continuously variable transmission. Pulley strain was analyzed by analytical method and finite element analysis. The results indicate that with the increase of transmission ratio, the driver pulley compressive strain is increases after reduces for a while, and the driven pulley increase. Compressive strain dense when radius is lesser and vice versa. Two methods results are basically the same, whereby demonstrating that the model is rational and that the analysis results are reliable.

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Optogenetic photochemical control of designer K+ channels in mammalian neurons

Journal of Neurophysiology ◽

10.1152/jn.00251.2011 ◽

2011 ◽

Vol 106 (1) ◽

pp. 488-496 ◽

Cited By ~ 40

Author(s):

Doris L. Fortin ◽

Timothy W. Dunn ◽

Alexis Fedorchak ◽

Duane Allen ◽

Rachel Montpetit ◽

...

Keyword(s):

Ion Channels ◽

Attachment Site ◽

Light Sensitivity ◽

Neuronal Firing ◽

Chemical Genetic ◽

M Current ◽

Azobenzene Moiety ◽

Tethered Ligand ◽

Firing Properties

Currently available optogenetic tools, including microbial light-activated ion channels and transporters, are transforming systems neuroscience by enabling precise remote control of neuronal firing, but they tell us little about the role of indigenous ion channels in controlling neuronal function. Here, we employ a chemical-genetic strategy to engineer light sensitivity into several mammalian K+ channels that have different gating and modulation properties. These channels provide the means for photoregulating diverse electrophysiological functions. Photosensitivity is conferred on a channel by a tethered ligand photoswitch that contains a cysteine-reactive maleimide (M), a photoisomerizable azobenzene (A), and a quaternary ammonium (Q), a K+ channel pore blocker. Using mutagenesis, we identify the optimal extracellular cysteine attachment site where MAQ conjugation results in pore blockade when the azobenzene moiety is in the trans but not cis configuration. With this strategy, we have conferred photosensitivity on channels containing Kv1.3 subunits (which control axonal action potential repolarization), Kv3.1 subunits (which contribute to rapid-firing properties of brain neurons), Kv7.2 subunits (which underlie “M-current”), and SK2 subunits (which are Ca2+-activated K+ channels that contribute to synaptic responses). These light-regulated channels may be overexpressed in genetically targeted neurons or substituted for native channels with gene knockin technology to enable precise optopharmacological manipulation of channel function.

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