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P Grigg

Publications and source records attributed to P Grigg.

At least 37 records · Page 2Linked to original sources
PubMed1996

Mechanical states encoded by stretch-sensitive neurons in feline joint capsule.

1. The sensitivity of group II joint afferents innervating cat knee joint capsule to in-plane stretch was studied in vitro. Single afferents were recorded from teased filaments of the posterior articular nerve. The capsule was stretched by applying forces through tabs along the edges of the capsule (3 tabs/edge) with the use of an apparatus that allowed for independent control of each load. The relationships between the neural responses of these afferents and the local continuum mechanical state of the joint capsule have been investigated. By appropriately loading the tissue margins, it was possible to establish states of uniaxial and biaxial tension, including shear. 2. Plane stress was calculated from the loads along the tissue margins. Stress at the location of the mechanoreceptor ending was estimated by interpolation. Strain was calculated from deformations of the capsule measured by tracking markers on its surface. Full characterization of tissue stress and strain made it possible to determine strain energy density and the magnitudes of other coordinate invariant mechanical quantities. 3. Individual afferents (n = 15) exhibited pronounced selectivity to the direction of applied stress and strain. There was no overall preferred orientation across neurons, and simple correlation of individual stress or strain components with the neuronal response revealed no consistent relationship between neuronal response and any single tensor component. However, linear multiple regression of the combined stress and strain components with the neuronal response revealed high correlation (mean R = 0.91), indicating that the measured mechanical states strongly determine the neuronal response. There was a much stronger relationship between neuronal response and stress variables than with strain variables. Simple correlation of the first invariant of the stress tensor with neuronal response had the highest mean correlation of the tensor quantities (R = 0.51). On average, strain energy density was only modestly correlated with the neural response (R = 0.28). 4. These findings indicate that capsule mechanoreceptors are encoding the local continuum mechanical state in the joint capsule. The neural response of these mechanoreceptors is more strongly correlated to local stress than to local strain.

Adaptation, Physiological↗
PubMed1996

Noise-enhanced information transmission in rat SA1 cutaneous mechanoreceptors via aperiodic stochastic resonance.

1. Aperiodic stochastic resonance (ASR) is a phenomenon wherein the response of a nonlinear system to a weak aperiodic input signal is optimized by the presence of a particular, nonzero level of noise. Our objective was to demonstrate ASR experimentally in mammalian cutaneous mechanoreceptors. 2. Experiments were performed on rat slowly adapting type 1 (SA1) afferents. Each neuron was subjected to a perithreshold aperiodic stimulus plus noise. The variance of the noise was varied between trials. The coherence between the aperiodic input stimulus and the response of each SA1 afferent was computed. 3. Of the 12 neurons tested, 11 showed clear ASR behavior: as input noise variance was increased, the stimulus-response coherence rapidly increased to a peak and then slowly decreased. These findings were in contrast with those for the average firing rate, which increased monotonically as a function of input noise variance. 4. This work shows that noise can serve to enhance the response of a sensory neuron to a perithreshold aperiodic input signal. These results suggest a possible functional role for input noise in sensory systems. These findings also indicate that it may be possible to introduce noise artificially into sensory neurons to improve their abilities to detect arbitrary weak signals.

Animals↗
PubMed1996

Stretch sensitivity of mechanoreceptor neurons in rat hairy skin.

1. Cutaneous mechanoreceptor neurons were recorded in a preparation of isolated rat skin while the skin was stretched with an apparatus that allowed the parameters of tensile stress and strain to be controlled. 2. SA2 afferents were strongly directionally selective in response to stretch. Their responses were correlated most strongly with the tensile stress along the unit's preferred direction and were related poorly to strain variables. Threshold tensile stresses required to activate SA2s were low, on the order of 5 kPa. 3. C-mechanoreceptors were stretch activated. They lacked directional selectivity and had tensile stress thresholds similar to SA2s. 4. Hair afferents had only dynamic responses to stretch. SA1 afferents were not stretch activated.

Afferent Pathways↗
PubMed1994

A computer-based orthodontic learning package: report of a trial.

Computer-based teaching has been used in the Department of Child Dental Health of the University of Bristol Dental School for almost 10 years to provide students with additional practice in the assessment of malocclusion and the planning of orthodontic treatment. In this article, the authors describe a study of the usefulness of computer-based learning packages for general practitioners and offer guidelines for others wishing to set up such a scheme.

Adult↗
PubMed1993

Loading and deformation of the cat posterior knee joint capsule in axial and extension rotations.

Deformation and loading of the knee posterior joint capsule were studied in the cat, in extension rotations and in axial external (ER) and internal (IR) rotations at full extension. Loads were measured in the ligament along the upper edge of the capsule, using mechanically sensitive neurons that were calibrated as load cells. Strains were measured across the surface of the capsule, by tracking a set of markers attached to its surface. External rotations produced small loads in the cable: with applied moments of up to 0.25 Nm, cable tensions were less than 0.8 mPa. The cable was not loaded by internal rotations. Axial rotations produced predominantly shear strains in the capsule. Extension produced small loads in the ligament and the predominant capsule strain was tensile along the axis of the femur. These results show that the posterior capsule has a small role in resisting extension, a minimal role in providing axial stability in ER, and no such role in IR.

Animals↗
PubMed1991

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.

Anesthesia↗
PubMed1989

Calibrating joint capsule mechanoreceptors as in vivo soft tissue load cells.

A method has been developed whereby the discharge of mechanically sensitive neurons from the cat knee joint capsule can be calibrated and used as load cells. The neurons are located in the upper edge of the capsule which has been previously modeled as a suspension cable and where the loading has been shown to be one dimensional. The calibration procedure relies upon applying known point loads to the cable and measuring its shape. The biomechanical model is then used to compute the cable tension at the neuron location. Results for 20 neurons showed a strong linear relationship between the tension and the frequency of neuronal discharge (r = 0.96, S.D. = 0.05). For 11 of these neurons the in vivo calibration was verified by subsequently excising the posterior capsule and recording from the same neuron while subjecting the cable to measured uniaxial loads. Results showed good agreement between the in vivo and in vitro calibrations. Once calibrated these neurons can be used as load sensors to study in vivo joint loading.

Animals↗
PubMed1989

Measurement of joint capsule tissue loading in the cat knee using calibrated mechanoreceptors.

The vertical loading in the posterior capsule of the cat knee has been measured while the knee is rotated into hyperextension. Tissue loading was determined using a previously verified model of the capsule that represents its upper edge as a catenary suspension cable. Tensile loads in the cable were measured using the discharge of mechanoreceptive sensory neurons that had been calibrated as load sensors. The results revealed that the capsule is very lightly loaded in extension rotations. Less than 4% of the applied moment is sustained by the capsule.

Animals↗
PubMed1989

The contribution of articular receptors to proprioception with the fingers in humans.

1. Whether joint receptors contribute demonstrably to proprioception has remained uncertain. Therefore, we tested whether an articular contribution to movement sense could be revealed if the total sensory input available to signal joint movement were reduced by eliminating movement signals from muscles. With a reduced sensory input, whatever contribution articular receptors made to proprioception ought to assume a greater-than-normal importance, and any effect of eliminating articular inputs should become more apparent. The distal interphalangeal joint of the middle finger was used, because the muscles could be decoupled from this joint by positioning the fingers to slacken the tendons. 2. To further enhance the possibility for observing an effect of eliminating articular contributions, we planned to test movement sense at positions of the joint in which the articular receptors would be most active. However, the response properties of receptors in primate finger joints were unknown, so we examined activity of receptors in finger joints of monkeys prior to testing humans. 3. Activity of receptors in interphalangeal joints of monkeys was measured over a wide range of positions before and during local anesthesia of the joint. Little response was seen over intermediate positions, but activity increased as the joint approached full flexion or full extension in much the same manner as responses previously observed with receptors in the knee, elbow, wrist, and hip joints. Local anesthetic injected into the joint space abolished the nerve activity. 4. Proprioception was tested in humans before and during local anesthesia of the joint using a movement-detection paradigm.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1986

Biophysical studies of mechanoreceptors.

Mechanoreception can be viewed as a series of sequential mechanical and ionic processes that take place in mechanosensitive end organs and in the terminals of the nerves that innervate them. Stimuli act on a transducer after being transmitted through some material having a combination of elastic and viscoelastic properties. Channels that open under membrane loading have recently been described in muscle cells and are presented as a model for transduction. When open these channels are cation specific. Ions passing through transducer channels depolarize a spike-initiating zone on the cell. These currents may also activate other conductances in the cell, so that the total generator current may have many components. In many mechanoreceptors, action potential initiation results in activation of an electrogenic Na+ pump at the spike-initiation zone, which modifies the threshold for subsequent action potentials. Action potentials initiated in the many branches of a single sensory axon interact at the branching point of the axon. The rules governing this interaction are complex. The above factors, together or separately, are responsible for the dynamic responses and adaptation observed in mechanoreceptors.

Action Potentials↗
PubMed1986

Mechanical sensitivity of group III and IV afferents from posterior articular nerve in normal and inflamed cat knee.

Recordings were performed from sciatic nerve or dorsal root filaments in 28 cats to study single group III (conduction velocity 2.5-20 m/s) and group IV (conduction velocity less than 2.5 m/s) units supplying the knee joint via the posterior articular nerve (PAN). In seven of these cats the knee joint had been inflamed artificially. Recordings from sciatic nerve filaments revealed responses to local mechanical stimulation of the joint in only 3 of 41 group IV units and in 12 of 18 group III units from the normal joint. In the inflamed joint 14 of 36 group IV units and 24 of 36 group III units were excited with local mechanical stimulation. In recordings from dorsal root filaments (normal joint) 4 of 11 group IV units and 7 of 13 group III units were activated by stimulating the joint locally. In the normal joint four group IV units (recorded from dorsal root filaments) responded only to rotations against the resistance of the tissue, whereas the majority of the fibers did not respond even to forceful movements. Group III units with local mechanosensitivity in the normal joint reacted strongly or weakly to movements in the working range of the joint or only to movements against resistance of the tissue. In the inflamed joint, group IV fibers (recorded in sciatic nerve filaments) with detectable receptive fields responded strongly to gentle movements or only to movements against resistance of tissue. Some did not react to movements. Group III units reacted strongly or weakly to gentle movements or only to movements against resistance of the tissue.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1985

A biomechanical model of the posterior knee capsule of the cat.

A biomechanical model is presented which represents the upper edge of the posterior knee capsule in the cat as a two-segment, vertically loaded catenary suspension cable from which the capsule sheet is suspended. Data are presented which show that the upper edge of the capsule is organized as a cable, which spans the notch between the femoral condyles. When a point load is applied to the cable, measurement of the cable shape allows for calculation of the cable tension and the downward distributed loads acting on the cable. This method was used to measure the in-vivo cable tension and the distributed downward loading acting on the capsule cable. The results show that the lateral side of the posterior joint capsule sustains a higher loading than the medial side.

Animals↗
PubMed1984

In vivo strain patterns in the four major canine knee ligaments.

Using mercury gauges, we measured strains in vivo in the four major ligaments of the canine knee joint as the tibia was loaded in valgus or varus at fixed angles of knee flexion. Free axial rotation of the tibia on the femur was allowed. Forces up to 78.4 N were applied to the tibia, producing moments of approximately 9 N-m. We found that with valgus loading, significant strains were observed in the medial collateral ligament at extension. At 45 degrees of flexion, the medial collateral, posterior cruciate, and anterior cruciate were strained. At 90 degrees of flexion, all four ligaments were strained. With varus loading, significant strains were found in the lateral collateral and anterior cruciate at extension. The lateral collateral and anterior cruciate ligaments were strained at 45 degrees of flexion. At 90 degrees of flexion, the lateral collateral, anterior cruciate, and posterior cruciate ligaments were strained. With valgus loading, the tibia rotated internally and the degree of axial rotation increased with flexion. External rotation of the tibia resulted from varus loading, and was relatively constant through the range of flexion. Thus when axial rotation is allowed, stability of the knee in response to valgus and varus loads is maintained by the cruciates as well as the collaterals, and the role of the cruciates increases with flexion and axial rotation.

Animals↗
PubMed1984

A method for measuring strains in soft tissue.

A finite element based method has been developed for measuring strains in soft tissue. An array of markers is placed on the tissue surface and treated as nodes of a four node isoparametric element. The displacements of the marker centroids are directly measured using a high sensitivity television camera. Finite element method mathematics are then used to calculate the plane strain tensor at any point inside the element. The method has been implemented using non-rectangular elements that are approximately 2 mm on each side.

Animals↗
PubMed1984

Ruffini mechanoreceptors in isolated joint capsule: responses correlated with strain energy density.

Mechanoreceptive afferents innervating the posterior capsule of the cat knee joint were recorded in a preparation of isolated capsule. The purpose of the experiments was to identify mechanical states in the capsule that were associated with afferent discharge. The capsule was excised from the knee with its bone attachments intact, so that the geometry of the capsule could be reproduced in vitro. The capsule was deformed, and measurements were made of stresses and strains in the plane of the capsule. Afferent discharge was correlated with each of the components of plane stress, plane strain, and strain energy density (SED). SED, the stored elastic energy at the receptor location, was the only mechanical variable that was consistently positively correlated with afferent discharge. A model of the Ruffini-type receptor is presented that accounts for the sensitivity to SED.

Afferent Pathways↗
PubMed1978

Segmental reflexes mediated by joint afferent neurons in cat knee.

1. Reflex effects mediated by knee joint afferent neurons were tested using the electrically evoked monosynaptic reflex in motoneurons innervating muscles which act about the knee. 2. Joint afferents were excited using small extension movements of the knee, stimuli which have been shown to be effective in activating a large fraction of the myelinated fibers in joint nerves. Because of the variability of reflex responses observed by others under similar experimental conditions, experimental control and data collection were done automatically under computer control. Large numbers of trials were presented in random sequence, and the resulting data were sorted and averaged. 3. Positive feedback was observed in both knee extensor (vasti) and knee flexor (posterior biceps-semitendinosus (PB-ST)) motoneuron populations. Vasti motoneurons were excited, and PB-ST motoneurons were inhibited by knee extensions when the posterior articular nerve (PAN) was intact; these effects were lost or substantially reduced when the PAN was cut. 4. Using knee extension stimuli, no reliable reflex effects were observed which could be attributed to afferents in medial articular nerve.

Animals↗