Population estimates for responses of cutaneous mechanoreceptors to a vertically indenting probe on the glabrous skin of monkeys

Recordings were obtained from low-threshold mechanoreceptive afferents during stimulation with a 0.5-mm-diameter probe at the receptive field (RF) center and at different distances from the point of maximal sensitivity. At each location, force-controlled stimuli of 0.5–4.0 g were ramped on to a plateau and then off at rates of 1, 10, and 100 g/s. The properties of rapidly adapting (RA) and slowly adapting type I (SAI) mechanoreceptors, when stimulated at the RF center, were similar in many respects to those reported in previous studies. Controlled stimulation away from the RF centers revealed that RF size for RAs was primarily dependent upon ramp rate, and for SAIs the size of the RF was primarily dependent upon load (force). The action potentials from individual afferents during stimulation at each location were binned in time and assigned to spatial segments of 1 mm. These responses were multiplied by: (A) an annular area of the receptive field and (B) the innervation density for the afferent type and skin region. The calculations provided estimates of overall rates of activity among the population of cutaneous afferents that respond to indentation by a small probe. Important differences were obtained between the responses of the population of afferents activated by the trapezoidal stimulus and the responses of afferents stimulated only at the RF center. Populations of tactile afferents provide more information for rate and intensity (force) discriminations than is available from units stimulated at the RF center. For RA afferents, the exponent of the power function describing relationships between stimulus rate and the population discharge (in impulses per second) was 0.3 times greater than the exponent for responses to on-center stimulation. For SAI mechanoreceptors, the exponent of the power functions for static responses to force was 0.22 times greater for the population responses than for on-center activation. Population functions for RA responses to the rate of force application and for SAI responses to static load saturated less than comparable responses to stimuation of the RF center. Thus, the coding capacity of the population extends the range of tactile discriminability. The slope and range of stimulus-response functions for populations was enhanced relative to responses to oncenter stimulation. This occurs because of recruitment of afferents with RF centers adjacent to and remote from the stimulus, depending upon thresholds and receptive field sizes for different stimulus parameters. With stimulation at increasing rates and forces, there is a progressive spatial recruitment of receptors. Over 90% of the activity elicited by suprathreshold punctate stimuli originated from mechanoreceptors with RF centers 1 mm or more away from the stimulus site. When the population response of SA afferents was calculated for different intensities of plateau stimulation, ranging from 1 to 4 g, the slope of the power function corresponded well to psychophysical estimates in the literature on the growth of touch intensity. Recruitment of afferents stimulated off the RF center shaped the temporal pattern of discharge. For RA afferents, the population response reached peak rates toward later portions of the onset and offset response than for on-center stimulation. For SAI afferents, the population discharge during slow onsets accelerated more positively than the responses to on-center stimulation. Variations in the rate, amplitude, and duration of stimulation were demonstrated to be useful in assessing the contribution of SAI and RA afferents to different tactile sensations. At very slow rates of stimulus application, the RA response was so minimal that the population response can be considered to arise from SAI afferents. At high stimulus rates, the population response was greatly accentuated during the onset (indentation) and offset (removal) of a trapezoidal ramp-and-hold stimulus, relative to firing rates during maintained indentation. Ratios of dynamic to static discharge were 3–4 times greater for the population than for on-center stimulation, reaching values as high as 60.21. The ratios of dynamic to static population responses were greatest for stimuli presented to the palm and were least for stimuli presented to the base and middle phalanges of the fingers. Therefore, the relative magnitudes of onset, offset, and steadystate sensations elicited by stimulation at different rates and locations should vary systematically, according to the absolute and relative densities of each receptor type.     

Encoding of compressive stress during indentation by slowly adapting type I mechanoreceptors in rat hairy skin

The mechanical state encoded by slowly adapting type 1 mechanoreceptors (SAI) during indentation was examined using an isolated preparation in a rat model. Skin and its intact innervation were harvested from the medial thigh of the rat hindlimb and placed in a dish, with the corium side down, containing synthetic interstitial fluid. The margins of the skin were coupled to an apparatus that could stretch and apply compression to the skin. Using a standard teased nerve preparation, the neural responses of single SAIs were identified. SAIs were stimulated, using controlled compressive stress while simultaneously measuring displacement, by compressing the skin between indenters (flat cylinders) of different diameters and a hard platform. SAIs were subcategorized according to whether their neural response saturated above or below 10 kPa compressive stress (SAI-H or SAI-L, respectively). Linear regression was used to evaluate the relationships between neuron response and stress and force and displacement. For all SAIs, the mean neural response was significantly and substantially more highly correlated with compressive stress than force or displacement. For the SAI-L subcategory, the mean correlation coefficient was significantly and substantially greater for stress than for force but not significantly different for displacement. The data from this study support the hypothesis that SAI mechanoreceptors stimulated by indentation encode compressive stress rather than force, displacement, or strain.     

Quantitative analyses of dynamic strain sensitivity in human skin mechanoreceptors

Microneurographical recordings from 24 slowly adapting (SA) and 16 fast adapting (FA) cutaneous mechanoreceptor afferents were obtained in the human radial nerve. Most of the afferents innervated the hairy skin on the back of the hand. The afferents' receptive fields were subjected to controlled strains in a ramp-and-hold fashion with strain velocities from 1 to 64%.s(-1), i.e., strain velocities within most of the physiological range. For all unit types, the mean variation in response onset approached 1 ms for strain velocities >8%.s(-1). Except at the highest strain velocities, the first spike in a typical SAIII unit was evoked at strains <0.5% and a typical SAII unit began to discharge at <1% skin strain. Skin strain velocity had a profound effect on the discharge rates of all classes of afferents. The "typical" peak discharge rate at the highest strain velocity studied was 50-95 imp/s(-1) depending on unit type. Excellent fits were obtained for both SA and FA units when their responses to ramp stretches were modeled by simple power functions (r2 > 0.9 for 95% of the units). SAIII units grouped with SAII with respect to onset latency and onset variation but with SAI units with respect to dynamic strain sensitivity. Because both SA and FA skin afferents respond strongly, quickly, and accurately to skin strain changes, they all seem to be able to provide useful information about movement-related skin strain changes and therefore contribute to proprioception and kinesthesia.     

Response of joint capsule neurons to axial stress and strain during dynamic loading in cat

1. Experiments were conducted to test the hypothesis that the responses of joint capsule mechanoreceptors better encode tissue stress or tissue strain. The experimental model was a small ligament from the cat knee capsule, which was stretched uniaxially in vitro. Experiments were done with either force or displacement as the controlled variable, and with steps, sinusoids, or pseudorandom Gaussian noise (PGN) as the input function. 2. The strength of coupling between neural discharge and both strain and stress was quantified during step experiments using linear correlation coefficients. The correlation between the frequency of neural discharge and stress was 0.93 +/- 0.09 (SD). The correlation between frequency of neural discharge and strain was -0.91 +/- 0.06. The magnitudes of these correlation coefficients were not significantly different. 3. The strength of coupling between neural discharge and both strain and stress during sinusoidal and PGN experiments was quantified by the use of an information theoretic statistic, transinformation. Out of 282 sinusoidal runs, transinformation between neural discharge and stress was significantly greater than transinformation between strain and neural discharge 241 times. Transinformation between strain and neural discharge was significantly greater 15 times. 4. During PGN experiments, transinformation between stress and neural discharge was greater than transinformation between strain and neural discharge in all 19 experimental runs. 5. Conditional transinformation between strain and neural discharge, given stress, was calculated for all sinusoidal and pseudorandom experiments. This statistic was greater than zero in 268 out of 289 experimental runs, indicating that a component of strain independent of stress is being signaled in the neural discharge.     

The neural signal of angular head position in primary afferent vestibular nerve axons

1. The relation between discharge frequency and angular head position was determined for a population of regularly discharging single first-order vestibular neurones in the eighth nerve of the barbiturate anaesthetized cat.2. Each axon had a characteristic head position which was maximally excitatory to it, and a diametrically opposed head position which was minimally excitatory.3. After correction for phase shifts introduced by the orientation of preferred excitability, discharge rate in statoreceptor afferents varied as a power function of the sine of angular head position with exponents ranging from 0.9 to 1.6.4. Experimentally determined discharge rates were compared with the predictions of a computer simulation model incorporating the idea that shearing force acting on morphologically polarized receptors is the adequate stimulus for macular receptor cells.5. This approach permitted the identification of a population of first-order vestibular afferents whose discharge frequency varied with head position as did the magnitude of shear force computed for individual receptors, each most excited in a particular head position.6. The majority of the spatial orientations of maximal sensitivity defined a surface which is tilted by approximately 30 degrees with reference to the Horsley-Clarke horizontal plane, implying that most statoreceptor afferents are maximally sensitive to position changes when the cat's head is at or near its normal position.     

Encoding of amplitude and rate of tooth loads by human periodontal afferents from premolar and molar teeth

Microneurographic recordings were obtained from 20 periodontal mechanoreceptive afferents in the inferior alveolar nerve while force profiles of different amplitudes and rates were applied to a premolar or the first molar in the most sensitive direction. The majority of afferents (17/20) showed a hyperbolic relationship between the steady-state discharge rate and the amplitude of the stimulating force, featuring a pronounced saturation tendency. These afferents were also characterized by a similar decline in dynamic sensitivity with increasing amplitude of background force. However, a few afferents (3/20) showed nearly linear stimulus-response relationships and a small decline in dynamic sensitivity with increasing tooth load. Quantitative models developed for all afferents successfully predicted the afferent discharge rates for novel force stimulations. Application of the transfer function to chewing forces predicted that the discharge rates of periodontal afferents rapidly increased at initial tooth contact and continued to discharge as long as the tooth was loaded. However, due to the marked saturation tendencies at higher forces, most periodontal afferents poorly encoded the magnitude of the strong chewing forces. In addition, the discharge rates of a minority of afferents continued to reflect the force profile during high chewing forces. The results revealed that periodontal afferents of posterior teeth were less sensitive at low tooth loads compared with afferents of anterior teeth. During each chewing cycle, periodontal afferents may provide information about the mechanical properties of food shortly after tooth contact that can be used to scale the muscle commands of the upcoming power phase.     

Impulse technique for dynamic measurements of muscular structures in biomechanical applications

Impulse techniques (using modern low-impedance quartz transducers and minicomputers) greatly simplify the dynamic testing of mechanical structures. The impact method involves striking the test object with a hammer, measuring the impact force and resultant motion (acceleration, velocity or displacement) at points of interest, then automatically computing and plotting the transfer characteristic, compliance (XIF) or impedance (F/V) as a function of frequency. Results show resonance, vibration mode shapes and dynamic stiffness, which relate displacement to the force causing it. In this system, a force transducer instrumented hammer conveniently generates a force impulse when striking the test object. This impulse approach saves considerable time over the more conventional and laborious sweep frequency methods. In advanced research measurements and in biomechanical applications such as on limbs a long measurement time is not acceptable because of the variability of the muscle structure. The paper describes the proposed technique applied to the muscular structures and reports clinical results on hemiplegic patients during a rehabilitative treatment with functional electrical stimulation.     

Single unit responses and the total afferent outflow from the cat's foot pad upon mechanical stimulation

Summary The properties of mechanosensitive units with large myelinated afferents were determined in the hairless skin of the central pad of the cat's hind foot, and the total afferent outflow from this region after short skin indentations and during constant force stimuli was measured in the plantar nerves.Basically three types of mechanosensitive units with afferent conduction velocities above 40 m/s were found: (a) receptors with the properties of Pacinian corpuscles (PC-receptors); (b) receptors which showed burst discharges for up to 500 ms after the onset of a constant force stimulus (RA-receptors); and (c) receptors which discharged throughout a constant force stimulus (SA-receptors).The afferent conduction velocities of these units were in the same range as those of receptors from the surrounding hairy skin. A considerable proportion of receptors from both skin areas had no collaterals in the dorsal columns.The afferent outflow after short skin indentations of up to 5 displacement consisted of impulses from PC-receptors only. Stimuli of 20 recruited between 50 and 100 afferent units of which less than 10% were other than PC-units. During constant force stimuli the afferent outflow came from SA-receptors only. Ten seconds after stimulus onset a 500 g stimulus evoked an afferent discharge of about 1000 imp/s and a 1000 g stimulus of about 1700 imp/s. At all times a power function of the form F=K · (S–S₀)ⁿ related the afferent discharge F to the stimulus intensity S. The exponents were around n=0.5 and tended to increase in the course of the stimulus.This work was supported by the Deutsche Forschungsgemeinschaft.     

On the mechanical power of joint extensions as affected by the change in muscle force (or cross-sectional area), ceteris paribus

This paper offers a reference prediction for the changes of mechanical power generated during a maximal (vertical, horizontal or inclined) joint extension, as a consequence of just the changes of muscle force or cross-sectional area (CSA). Ceteris paribus (all other things being equal), for a given joint, the exponents at which the force changes have to be raised to predict the duration, final speed and power of the maximal extension are –0.5, 0.5, and 1.5, respectively, for horizontal movements. For example, a force decrease of 30% leads to an increase of 19.5% of the duration of the extension and to a decrease of 16.3% and of 41.4% of its final speed and power. The equations for vertical or inclined extension performances are subject to the same exponents. However, the actual prediction is dependent upon the ratio between muscle strength and body weight, reflecting the fraction of the muscle strength (or CSA) acting against gravity during the manoeuvre. For instance, during a vertical extension, a force decrease of 30% leads to an increase of 30.9% of the duration of the extension and to a decrease of 29.3% and of 50.5% of its final speed and power. Based on the proposed model, a methodology is also described to detect the effects on the extension power of other determinants, in addition to CSA, of the useful force change (e.g. neuromuscular factors, motor control). Electronic Publication     

基于F-Scan三维动态足底压力分析系统的动静态足底压力分析

背景：有研究表明足的部分解剖区域支撑着人体大部分质量,并调节着人体的平衡,测量这些区域的压强峰值及分布即可获取足、下肢乃至全身的生理、结构及功能等方面的大量信息。 目的：观察健康青少年足球运动员自然行走时左右足峰力值、负荷冲量等的动态足底压力分布。 方法：采用三维动态足底压力步态分析系统对16~19岁适龄青少年足球运动员进行动态足底压力测试。 结果与结论：受试者足底应力-时间曲线呈明显的双峰型,足底10个分析区域峰力均值在足跟外侧最大(P < 0.01),右足习惯者第1 趾、第1,2 跖骨、足跟内外侧区域平均峰力值右足大于左足(P < 0.05),而第5跖骨、足弓2个区域平均峰力值左足大于右足(P < 0.05)。受试者行走时整足接触阶段、离地阶段负荷中心在第1、2跖骨、足跟内外侧区域,足部最大负荷部位在第1、2跖骨、足跟内外侧区域,男女左右足分布规律基本一致。结果证实,健康青少年足球运动员左右足动态与静态足底压力分布规律存在一致性特征。     

Effects of fusimotor stimulation on dynamic and position sensitivities of spindle afferents in the primate.

The effects of stimulation of single static and dynamic fusimotor fibers on the dynamic sensitivity and position sensitivity of primary and secondary spindle afferents have been studied in the soleus muscle of the baboon. Static fusimotor fibers decreased the mean dynamic sensitivity of primary afferents at all rates of stretch and stimulation. The magnitude of the decrease in dynamic sensitivity increased as the rate of fusimotor stimulation was increased. Qualitatively similar effects were observed in secondary afferents. Static fusimotor stimulation had a strong excitatory effect on spindle afferent resting discharge and greatly increased the mean position sensitivity of both primary and secondary afferents. Dynamic fusimotor fibers increased the mean dynamic index of primary afferents at all rates of stretch and stimulation. The effect of dynamic fusimotor fibers on the mean dynamic sensitivity, however, was dependent on the rate of muscle stretch; at rates below 15 mm/s the dynamic sensitivity was substantially increased, whereas at rates greater than 15 mm/s it was either unchanged or decreased. Dynamic fusimotor fibers slightly decreased the mean position sensitivity of primary afferents.     

Role of limb movement in the modulation of motor unit discharge rate during fatiguing contractions

Motor unit firing rates of the triceps brachii muscle have been shown to decline during sustained isometric contractions, but not if the fatiguing contraction incorporates arm movements. The purpose of this study was to determine the impact of the actual physical displacement of the limb on the maintenance of motor unit discharge rate during dynamic muscle fatigue. An isometric force pulse paradigm was used to recreate the motor unit activity patterns that occur during a dynamic contraction. With this paradigm, the variable force output that would occur during a dynamic contraction remained intact, but the movement of the limb was eliminated. Motor unit firing rates declined in the isometric force pulse protocol. Thus, factors related to the actual movement of the limb appear to enable the maintenance of motor unit discharge rates during fatigue.     

Investigation of using a power function as a cost function in inverse planning optimization

The purpose of this paper is to investigate the use of a power function as a cost function in inverse planning optimization. The cost function for each structure is implemented as an exponential power function of the deviation between the resultant dose and prescribed or constrained dose. The total cost function for all structures is a summation of the cost function of every structure. When the exponents of all terms in the cost function are set to 2, the cost function becomes a classical quadratic cost function. An independent optimization module was developed and interfaced with a research treatment planning system from the University of North Carolina for dose calculation and display of results. Three clinical cases were tested for this study with various exponents set for tumor targets and sensitive structures. Treatment plans with these exponent settings were compared, using dose volume histograms. The results of our study demonstrated that using an exponent higher than 2 in the cost function for the target achieved better dose homogeneity than using an exponent of 2. An exponent higher than 2 for serial sensitive structures can effectively reduce the maximum dose. Varying the exponent from 2 to 4 resulted in the most effective changes in dose volume histograms while the change from 4 to 8 is less drastic, indicating a situation of saturation. In conclusion, using a power function with exponent greater than 2 as a cost function can effectively achieve homogeneous dose inside the target and/or minimize maximum dose to the critical structures.     

Myosin light-chain phosphorylation and potentiation of dynamic function in mouse fast muscle

The intent of this study was to determine if the stimulation-induced increase or “potentiation” of dynamic function of mouse extensor digitorum longus muscle (in vitro 25°C) during work cycles is graded to myosin regulatory light-chain (RLC) phosphorylation. To do this, concentric force and muscle work output during sinusoidal length changes were determined before (unpotentiated) and after (potentiated) the application of conditioning stimuli (CS) producing incremental elevations in RLC phosphorylation from rest. Sine wave excursion was from 1.09 to 0.91 of L _o with a period of 142 ms; stimulating muscles to twitch and generate force during these cycles produced plots of force × displacement termed work loops. Stimulation at 2.5-, 5.0-, and 100-Hz elevated RLC phosphorylation from 0.16 ± 0.02 (rest) to 0.29 ± 0.03, 0.45 ± 0.02 and 0.56 ± 0.02 mol phos per mole RLC, respectively (n = 6–7, P < 0.05). These CS potentiated mean concentric force (at all lengths) to 1.14 ± 0.02, 1.26 ± 0.04 and 1.41 ± 0.06 of pre-stimulus, control levels (all n = 5–7, P < 0.05) while work was increased to 1.07 ± 0.02, 1.17 ± 0.02 and 1.34±0.03 of controls, respectively. In a No CS condition that did not elevate RLC phosphorylation, neither mean concentric force nor work was altered. Thus, strong correlations between RLC phosphorylation and mean concentric force and work support the hypothesis that this molecular mechanism modulates muscle power output. No length-dependence for concentric force potentiation was observed in any condition, an outcome suggesting that interactions between instantaneous variations in muscle length and shortening velocity during work cycles modulates the potentiation response.     

Dissociated effects of diazepam and lorazepam on short-latency afferent inhibition

Peripheral nerve inputs have an inhibitory effect on motor cortex excitability at short intervals (short-latency afferent inhibition, SAI). This can be tested by coupling electrical stimulation of peripheral nerve with transcranial magnetic stimulation (TMS) of the motor cortex. SAI is reduced by the anticholinergic drug scopolamine, and in patients with Alzheimer's disease. Therefore, it is possible that SAI is a marker of central cholinergic activity important for memory function. The benzodiazepine lorazepam also reduces SAI. Since benzodiazepines impair memory formation, but do not do so uniformly, with a maximum amnesic effect after lorazepam but less or no effect after diazepam, we were interested in testing in this non-behavioural study to what extent the effects of lorazepam and diazepam on circuits involved in SAI could be dissociated. In addition, and for control, we tested the effects of lorazepam and diazepam on short-interval intracortical inhibition (SICI), a motor cortical inhibition mediated through the GABA_A receptor. Lorazepam markedly reduced SAI, whereas diazepam slightly increased it. In contrast, both benzodiazepines uniformly increased SICI. Our findings demonstrate opposite effects of lorazepam and diazepam on SAI, an inhibition modulated by central cholinergic activity, but the same effects on SICI, a marker of neurotransmission through the GABA_A receptor. This dissociation suggests, for the first time, that TMS measures of cortical inhibition provide the opportunity to segregate differences of benzodiazepine action in human central nervous system circuits.     

Mitral Valve Function and Chordal Force Distribution Using a Flexible Annulus Model: An <Emphasis Type="Italic">In Vitro</Emphasis> Study

Since variations in annular motion/shape and papillary muscle displacement have been observed in studies of dilated cardiomyopathy and ischemic mitral regurgitation, the objective of this study was to investigate the effects of annular motion/flexibility and papillary muscle displacement on chordal force and mitral valve function. Six human mitral valves were studied in a left heart simulator using a flexible annular model. Mitral flow, trans-mitral pressure and chordae tendineae tension were monitored online in normal and pathophysiologic papillary muscle positions. The flexible annulus model showed a significant increase in mitral regurgitation volume (p < 0.05) when compared to static annuli models. Furthermore, there was a significant increase of force on the basal chords compared to the force present with the static annuli models. Utilizing the flexible annulus model, papillary muscle displacement significantly increased the force on the anterior strut, posterior intermediate and commissural chords. (1) Papillary muscle displacement increases the tension on the intermediate chords inducing tenting of the leaflets and subsequent regurgitation. (2) The tension on the intermediate and marginal chords is relatively insensitive to annular motion, whereas tension on the basal chords is directly affected by annular motion.     

Influence of mesh density,cortical thickness and material properties on human rib fracture prediction

The purpose of this paper was to investigate the sensitivity of the structural responses and bone fractures of the ribs to mesh density, cortical thickness, and material properties so as to provide guidelines for the development of finite element (FE) thorax models used in impact biomechanics. Subject-specific FE models of the second, fourth, sixth and tenth ribs were developed to reproduce dynamic failure experiments. Sensitivity studies were then conducted to quantify the effects of variations in mesh density, cortical thickness, and material parameters on the model-predicted reaction force–displacement relationship, cortical strains, and bone fracture locations for all four ribs. Overall, it was demonstrated that rib FE models consisting of 2000–3000 trabecular hexahedral elements (weighted element length 2–3 mm) and associated quadrilateral cortical shell elements with variable thickness more closely predicted the rib structural responses and bone fracture force–failure displacement relationships observed in the experiments (except the fracture locations), compared to models with constant cortical thickness. Further increases in mesh density increased computational cost but did not markedly improve model predictions. A ±30% change in the major material parameters of cortical bone lead to a ?16.7 to 33.3% change in fracture displacement and ?22.5 to +19.1% change in the fracture force. The results in this study suggest that human rib structural responses can be modeled in an accurate and computationally efficient way using (a) a coarse mesh of 2000–3000 solid elements, (b) cortical shells elements with variable thickness distribution and (c) a rate-dependent elastic–plastic material model.     

Myofascial force transmission in dynamic muscle conditions: effects of dynamic shortening of a single head of multi-tendoned rat extensor digitorum longus muscle

This study investigated the effects of myofascial force transmission during dynamic shortening of head III of rat extensor digitorum longus muscle (EDL III). The anterior crural compartment was left intact. Force was measured simultaneously at the distal EDL III tendon, the proximal EDL tendon and the distal tendons of tibialis anterior and extensor hallucis longus muscles (TA+EHL). Two types of distal shortening of EDL III were studied: (1) sinusoidal shortening (2 mm) and (2) isokinetic shortening (8 mm). Sinusoidal shortening of EDL III caused a decrease in force exerted at the distal tendon of EDL III: from 0.58 (0.08) N to 0.26 (0.04) N. In contrast, hardly any changes in proximal EDL force and distal TA+EHL force were found. Maximal concentric force exerted at the distal tendon of EDL III was higher than maximal isometric force expected on the basis of the physiological cross-sectional area of EDL III muscle fibers (Maas et al. 2003). Therefore, a substantial fraction of this force must originate from sources other than muscle fibers of EDL III. Isokinetic shortening of EDL III caused high changes in EDL III force from 0.97 (0.15) N to zero. In contrast, changes in proximal EDL force were much smaller: from 2.44 (0.25) N to 1.99 (0.19) N. No effects on TA+EHL force could be shown. These results are explained in terms of force transmission between the muscle belly of EDL III and adjacent tissues. Thus, also in dynamic muscle conditions, muscle fiber force is transmitted via myofascial pathways.     

Ensemble discharge from Golgi tendon organs of cat peroneus tertius muscle

1. The responses of individual tendon organs of the cat peroneus tertius muscle to motor-unit contractions were recorded in anesthetized cats during experiments in which all the Ib-afferent fibers from the muscle had been prepared for recording in dorsal root filaments. This was possible because the cat peroneus tertius only contains a relatively small complement of approximately 10 tendon organs. 2. Motor units of different physiological types were tested for their effects on the whole population of tendon organs in the muscle. Effects of unfused tetanic contractions were tested under both isometric and anisometric conditions. Each motor unit activated at least one tendon organ, and each tendon organ was activated by at least one motor unit. Individual slow-type units were found to act on a single or two receptors, whereas a fast-type unit could activate up to six tendon organs. 3. In one experiment, the effects of 8 motor units on 10 tendon organs were examined. One fast-twitch, fatigue resistant (FR)-type unit acted on six tendon organs, of which four were also activated by another FR unit. The contraction of each unit, on its own, elicited a range of individual responses, from weak to strong. The discharge frequencies of individual responses displayed no clear relation with the strength of contraction, nor did they accurately represent the shape of force profiles. But when all the discharges were pooled, a fairly good correspondence appeared between variations of contractile force and variations of averaged discharge frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)