scholarly journals Thresholds of cutaneous afferents related to perceptual threshold across the human foot sole

2015 ◽  
Vol 114 (4) ◽  
pp. 2144-2151 ◽  
Author(s):  
Nicholas D. J. Strzalkowski ◽  
Robyn L. Mildren ◽  
Leah R. Bent
Keyword(s):  
Mechanical Properties ◽  
Receptive Field ◽  
Direct Relationship ◽  
Cutaneous Afferents ◽  
Close Coupling ◽  
Firing Threshold ◽  
Human Foot ◽  
Data Support ◽  
Perceptual Threshold ◽  
Field Location

Perceptual thresholds are known to vary across the foot sole, despite a reported even distribution in cutaneous afferents. Skin mechanical properties have been proposed to account for these differences; however, a direct relationship between foot sole afferent firing, perceptual threshold, and skin mechanical properties has not been previously investigated. Using the technique of microneurography, we recorded the monofilament firing thresholds of cutaneous afferents and associated perceptual thresholds across the foot sole. In addition, receptive field hardness measurements were taken to investigate the influence of skin hardness on these threshold measures. Afferents were identified as fast adapting [FAI ( n = 48) or FAII ( n = 13)] or slowly adapting [SAI ( n = 21) or SAII ( n = 20)], and were grouped based on receptive field location (heel, arch, metatarsals, toes). Overall, perceptual thresholds were found to most closely align with firing thresholds of FA afferents. In contrast, SAI and SAII afferent firing thresholds were found to be significantly higher than perceptual thresholds and are not thought to mediate monofilament perceptual threshold across the foot sole. Perceptual thresholds and FAI afferent firing thresholds were significantly lower in the arch compared with other regions, and skin hardness was found to positively correlate with both FAI and FAII afferent firing and perceptual thresholds. These data support a perceptual influence of skin hardness, which is likely the result of elevated FA afferent firing threshold at harder foot sole sites. The close coupling between FA afferent firing and perceptual threshold across foot sole indicates that small changes in FA afferent firing can influence perceptual thresholds.

scholarly journals Cutaneous afferent innervation of the human foot sole: what can we learn from single-unit recordings?

2018 ◽  
Vol 120 (3) ◽  
pp. 1233-1246 ◽  
Author(s):  
Nicholas D. J. Strzalkowski ◽  
Ryan M. Peters ◽  
J. Timothy Inglis ◽  
Leah R. Bent
Keyword(s):  
Receptive Field ◽  
Single Unit ◽  
Body Position ◽  
Experimental Manipulation ◽  
The Body ◽  
Standing Balance ◽  
Cutaneous Afferents ◽  
Proprioceptive Information ◽  
Human Foot ◽  
Cutaneous Feedback

Cutaneous afferents convey exteroceptive information about the interaction of the body with the environment and proprioceptive information about body position and orientation. Four classes of low-threshold mechanoreceptor afferents innervate the foot sole and transmit feedback that facilitates the conscious and reflexive control of standing balance. Experimental manipulation of cutaneous feedback has been shown to alter the control of gait and standing balance. This has led to a growing interest in the design of intervention strategies that enhance cutaneous feedback and improve postural control. The advent of single-unit microneurography has allowed the firing and receptive field characteristics of foot sole cutaneous afferents to be investigated. In this review, we consolidate the available cutaneous afferent microneurographic recordings from the foot sole and provide an analysis of the firing threshold, and receptive field distribution and density of these cutaneous afferents. This work enhances the understanding of the foot sole as a sensory structure and provides a foundation for the continued development of sensory augmentation insoles and other tactile enhancement interventions.

scholarly journals Cutaneous stimulation evokes long-lasting excitation of spinal interneurons in the turtle

1990 ◽  
Vol 64 (4) ◽  
pp. 1134-1148 ◽  
Author(s):  
S. N. Currie ◽  
P. S. Stein
Keyword(s):  
Spinal Cord ◽  
Receptive Field ◽  
Action Potential ◽  
Receptive Fields ◽  
Neural Mechanisms ◽  
Cutaneous Afferents ◽  
Cutaneous Stimulation ◽  
Single Action ◽  
Single Action Potential ◽  
Stimulation Of

1. We demonstrated multisecond increases in the excitability of the rostral-scratch reflex in the turtle by electrically stimulating the shell at sites within the rostral-scratch receptive field. To examine the cellular mechanisms for these multisecond increases in scratch excitability, we recorded from single cutaneous afferents and sensory interneurons that responded to stimulation of the shell within the rostral-scratch receptive field. A single segment of the midbody spinal cord (D4, the 4th postcervical segment) was isolated in situ by transecting the spinal cord at the segment's anterior and posterior borders. The isolated segment was left attached to its peripheral nerve that innervates part of the rostral-scratch receptive field. A microsuction electrode (4-5 microns ID) was used to record extracellularly from the descending axons of cutaneous afferents and interneurons in the spinal white matter at the posterior end of the D4 segment. 2. The turtle shell is innervated by slowly and rapidly adapting cutaneous afferents. All cutaneous afferents responded to a single electrical stimulus to the shell with a single action potential. Maintained mechanical stimulation applied to the receptive field of some slowly adapting afferents produced several seconds of afterdischarge at stimulus offset. We refer to the cutaneous afferent afterdischarge caused by mechanical stimulation of the shell as "peripheral afterdischarge." 3. Within the D4 spinal segment there were some interneurons that responded to a brief mechanical stimulus within their receptive fields on the shell with short afterdischarge and others that responded with long afterdischarge. Short-afterdischarge interneurons responded to a single electrical pulse to a site in their receptive fields either with a brief train of action potentials or with a single action potential. Long-afterdischarge interneurons responded to a single electrical shell stimulus with up to 30 s of afterdischarge. Long-afterdischarge interneurons also exhibited strong temporal summation in response to a pair of electrical shell stimuli delivered up to several seconds apart. Because all cutaneous afferents responded to an electrical shell stimulus with a single action potential, we conclude that electrically evoked afterdischarge in interneurons was produced by neural mechanisms in the spinal cord; we refer to this type of afterdischarge as "central afterdischarge." 4. These results demonstrate that neural mechanisms for long-lasting excitability changes in response to cutaneous stimulation reside in a single segment of the spinal cord. Cutaneous interneurons with long afterdischarge may serve as cellular loci for multise

An Investigation of Trained Neural Networks from a Neurophysiological Perspective

Perception ◽  
1989 ◽  
Vol 18 (6) ◽  
pp. 793-803 ◽  
Author(s):  
Ian R Moorhead ◽  
Nigel D Haig ◽  
Richard A Clement
Keyword(s):  
Neural Networks ◽  
Receptive Field ◽  
Direct Relationship ◽  
Back Propagation ◽  
Receptive Fields ◽  
Recognition System ◽  
Output Function ◽  
Back Propagation Algorithm ◽  
Propagation Algorithm ◽  
The Neural Networks

The application of theoretical neural networks to preprocessed images was investigated with the aim of developing a computational recognition system. The neural networks were trained by means of a back-propagation algorithm, to respond selectively to computer-generated bars and edges. The receptive fields of the trained networks were then mapped, in terms of both their synaptic weights and their responses to spot stimuli. There was a direct relationship between the pattern of weights on the inputs to the hidden units (the units in the intermediate layer between the input and the output units), and their receptive field as mapped by spot stimuli. This relationship was not sustained at the level of the output units in that their spot-mapped responses failed to correspond either with the weights of the connections from the hidden units to the output units, or with a qualitative analysis of the networks. Part of this discrepancy may be ascribed to the output function used in the back-propagation algorithm.

Computer Simulation of Nanoparticle Aggregate Fracture

2007 ◽  
Vol 1056 ◽  
Author(s):  
Takumi Hawa ◽  
Brian Henz ◽  
Michael Zachariah
Keyword(s):  
Mechanical Properties ◽  
Molecular Dynamics ◽  
Computer Simulation ◽  
Tensile Strength ◽  
Direct Relationship ◽  
Brittle Materials ◽  
Ductile Failure ◽  
Strain Behavior ◽  
Nanoparticle Aggregate ◽  
Nanoparticle Aggregates

ABSTRACTNanoparticle aggregates have been found to possess unique mechanical properties. Aggregates of metal nanoparticles can be strained up to 100% before failure, and even typically brittle materials are observed to have a ductile failure mode. In this effort two materials; namely silver and silicon, were chosen to represent ductile and brittle materials, respectively. Aggregates with 2 to 6 particles were simulated using the molecular dynamics (MD) algorithm to determine the stress-strain behavior of the aggregate. Many interesting observations are made including the negligible affect of strain rate on ultimate tensile strength, and the direct relationship between Young's modulus and nanoparticle size.

scholarly journals The Implication of Petrographic Characteristics on the Mechanical Behavior of Middle Eocene Limestone, 15th May City, Egypt

2020 ◽  
Vol 12 (22) ◽  
pp. 9710
Author(s):  
Abdelaziz El Shinawi ◽  
Peter Mésároš ◽  
Martina Zeleňáková
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Carbonate Rocks ◽  
Direct Relationship ◽  
Middle Eocene ◽  
Urban Expansion ◽  
Engineering Properties ◽  
Mechanical Parameters ◽  
Thin Sections ◽  
Limestone Bedrock

The construction purposes of carbonate rocks are considered a major aspect of using these bedrocks based on their mechanical behavior. Accordingly, the physical and mechanical characterization of Middle Eocene Limestone bedrock in the new urban area at the 15th May City, Egypt was studied to assess the suitability of the carbonate rocks for construction. This study has been carried out to investigate the effect of petrographic characteristics on mechanical properties. To achieve this objective, the intact 30 rock core samples from 15 boreholes were selected at different depths. Based on study of the selected samples in thin sections, the limestone in the area was classified as lime-mudstone, wackestone, and grainstone. Additionally, the uniaxial compressive strength (UCS) and Schmidt Rebound Hammer (Rn) were determined to detect the mechanical properties of the limestone bedrock. The measured parameters (UCS and Rn) demonstrated a high direct relationship with mudstone and a poor direct relationship with dolomite and high negative correlation with wackestone and grainstone. Therefore, the Middle Eocene Limestone bedrock is more durable and has medium-strength, which made it suitable for constructions. Regression analysis was performed to find out some linear relationship between mechanical properties (UCS) with petrographic characteristics. The study reveals significant positive correlation between UCS and Rn with mudstone in accordance higher values of regression coefficient (R2 = 0.91 and R2 = 0.036), and an inverse relationship of Rn with dolomite % (R2 = 0.89 and R2 = 0.02), respectively. Consequently, the strong confidence on the mechanical parameters opens the way for engineers to predict the mechanical parameters that are required for engineering properties of limestone for the urban expansion.

Single low-threshold afferents innervating the skin of the human foot modulate ongoing muscle activity in the upper limbs

2013 ◽  
Vol 109 (6) ◽  
pp. 1614-1625 ◽  
Author(s):  
Leah R. Bent ◽  
Catherine R. Lowrey
Keyword(s):  
Upper Limb ◽  
Muscle Activity ◽  
Reflex Response ◽  
Cutaneous Afferents ◽  
Type I ◽  
Triceps Brachii ◽  
Median Response ◽  
Plantar Surface ◽  
Human Foot ◽  
Low Threshold

We have shown for the first time that single cutaneous afferents in the foot dorsum have significant reflex coupling to motoneurons supplying muscles in the upper limb, particularly posterior deltoid and triceps brachii. These observations strengthen what we know from whole nerve stimulation, that skin on the foot and ankle can contribute to the modulation of interlimb muscles in distant innervation territories. The current work provides evidence of the mechanism behind the reflex, where one single skin afferent can evoke a reflex response, rather than a population. Nineteen of forty-one (46%) single cutaneous afferents isolated in the dorsum or plantar surface of the foot elicited a significant modulation of muscle activity in the upper limb. Identification of single afferents in this reflex indicates the strength of the connection and, ultimately, the importance of foot skin in interlimb coordination. The median response magnitude was 2.29% of background EMG, and the size of the evoked response did not significantly differ among the four mechanoreceptor classes ( P > 0.1). Interestingly, although the distribution of afferents types did not differ across the foot dorsum, there was a significantly greater coupling response from receptors located on the medial aspect of the foot dorsum ( P < 0.01). Furthermore, the most consistent coupling with upper limb muscles was demonstrated by type I afferents (fast and slowly adapting). This work contributes to the current literature on receptor specificity, supporting the view that individual classes of cutaneous afferents may subserve specific roles in kinesthesia, reflexes, and tactile perception.

Cooling reduces the cutaneous afferent firing response to vibratory stimuli in glabrous skin of the human foot sole

2013 ◽  
Vol 109 (3) ◽  
pp. 839-850 ◽  
Author(s):  
Catherine R. Lowrey ◽  
Nicholas D. J. Strzalkowski ◽  
Leah R. Bent
Keyword(s):  
Receptive Field ◽  
Balance Control ◽  
Receptor Activation ◽  
Type I ◽  
Human Foot ◽  
Receptor Response ◽  
Single Nerve ◽  
Before And After ◽  
Skin Receptors

Skin on the foot sole plays an important role in postural control. Cooling the skin of the foot is often used to induce anesthesia to determine the role of skin in motor and balance control. The effect of cooling on the four classes of mechanoreceptor in the skin is largely unknown, and thus the aim of the present study was to characterize the effects of cooling on individual skin receptors in the foot sole. Such insight will better isolate individual receptor contributions to balance control. Using microneurography, we recorded 39 single nerve afferents innervating mechanoreceptors in the skin of the foot sole in humans. Afferents were identified as fast-adapting (FA) or slowly adapting (SA) type I or II (FA I n = 16, FA II n = 7, SA I n = 6, SA II n = 11). Receptor response to vibration was compared before and after cooling of the receptive field (2–20 min). Overall, firing response was abolished in 30% of all receptors, and this was equally distributed across receptor type ( P = 0.69). Longer cooling times were more likely to reduce firing response below 50% of baseline; however, some afferent responses were abolished with shorter cooling times (2–5 min). Skin temperature was not a reliable indicator of the level of receptor activation and often became uncoupled from receptor response levels, suggesting caution in the use of this parameter as an indicator of anesthesia. When cooled, receptors preferentially coded lower frequencies in response to vibration. In response to a sustained indentation, SA receptors responded more like FA receptors, primarily coding “on-off” events.

scholarly journals Long-Term Performance of Utah Slanted Electrode Arrays and Intramuscular Electromyographic Leads Implanted Chronically in Human Arm Nerves and Muscles

2020 ◽  
Author(s):  
Jacob A. George ◽  
David M. Page ◽  
Tyler S. Davis ◽  
Christopher C. Duncan ◽  
Douglas T. Hutchinson ◽  
...  
Keyword(s):  
Receptive Field ◽  
Signal To Noise Ratio ◽  
Electrode Arrays ◽  
Neural Recordings ◽  
Long Term Performance ◽  
Term Performance ◽  
Recording Electrodes ◽  
Over Time ◽  
Field Location

AbstractObjectiveWe explore the long-term performance and stability of seven percutanous Utah Slanted Electrode Arrays (USEAs) and intramuscular recording leads (iEMGs) implanted chronically in the residual arm nerves and muscles of three human amputees as a means to permanently restore sensorimotor function after upper-limb.ApproachWe quantify the number of functional recording and functional stimulating electrodes over time. We also calculate the signal-to-noise ratio of USEA and iEMG recordings and quantify the stimulation amplitude necessary to evoke detectable sensory percepts. Furthermore, we quantify the consistency of the sensory modality, receptive field location, and receptive field size of USEA-evoked percepts.Main ResultsIn the most recent subject, involving USEAs with technical improvements, neural recordings persisted for 502 days (entire implant duration) and the number of functional recording electrodes for one USEA increased over time. However, for six out of seven USEAs the number of functional recording electrodes decreased within the first two months after implantation. The signal-to-noise ratio of neural recordings and electromyographic recordings stayed relatively consistent over time. Sensory percepts were consistently evoked over the span of 14 months, were not significantly different in size, and highlighted the nerves’ fascicular organization. The percentage of percepts with consistent modality or consistent receptive field location between sessions (~1 month apart) varied between 0–86.2% and 9.1–100%, respectively. Stimulation thresholds and electrode impedances increased initially but then remained relatively stable over time.SignificanceThis work demonstrates improved performance of USEAs, and provides a basis for comparing the longevity and stability of USEAs to that of other neural interfaces. Although USEAs provide a rich repertoire of neural recordings and sensory percepts, performance still generally declines over time. Future work should leverage the results presented here to further improve USEA design or to develop adaptive algorithms that can maintain a high level of performance.

Relationships between resting tension and mechanical properties of papillary muscle

1976 ◽  
Vol 231 (6) ◽  
pp. 1679-1685 ◽  
Author(s):  
G Templeton ◽  
R Adcock ◽  
JT Willerson ◽  
L Nardizzi ◽  
K Wildenthal ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Mechanical System ◽  
Papillary Muscle ◽  
Direct Relationship ◽  
Elastic Component ◽  
Papillary Muscles ◽  
Resting Tension ◽  
Experimental Apparatus ◽  
The Individual ◽  
The Relationship

The influence on mechanical properties of changes in resting tension over a range from 0.5 to 4.5 g was investigated in 12 isolated cat papillary muscles. At each resting tension, the muscles contracted isometrically with the exception of an externally applied sinusoidal stretch of 0.5% Lmax (deltaL) and 20 Hz. Stiffness (deltaT/deltaL) was determined from deltaL and the peak amplitudes (deltaT) of the individual cycles from the sinusoidal component of tension. Assuming that the muscle and experimental apparatus behaved as a linear second-order mechanical system, it was possible to divide stiffness into its elastic and viscous components. During rest, total stiffness and its components were linearly related to tension. During contraction, stiffness and its elastic component were linearly related to tension. Furthermore, increasing resting tension increased the intercept and decreased the slope of this linear stiffness-tension relationship. The relationship between viscous stiffness and tension during contraction is more complex in that it is a direct relationship at low resting tensions, but an inverse one at high resting tensions.

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