PubMed Health⌕ Search

Biomedical subjects

A G Fel'dman

Publications and source records attributed to A G Fel'dman.

At least 19 recordsLinked to original sources
PubMed1982

Interaction of afferent and efferent signals underlying joint position sense: empirical and theoretical approaches.

A model of joint position sense is considered based on the concept that central motor commands are adequately expressed in terms of shifts of the so-called invariant length-tension characteristics for agonist and antagonist muscles. The main points of this concept are discussed to clarify them and to prevent misunderstanding. The basic idea of the model is that the efferent copy of the central motor commands plays the role of a reference frame for evaluation of afferent proprioceptive discharges. An experiment with reproduction of constrained movements was performed in order to investigate the influence of voluntary flexor or extensor muscle tension on position sense in the elbow joint. The results demonstrate adequate perception of joint position on the background of voluntary muscle tension and thus are quite consistent with the model. The role of afferent and efferent signals in position sense is discussed with special reference to views expressed recently by different authors. The interrelation between position sense and sense of effort is considered, based on a concept of senso-motor space.

Journal Article↗
PubMed1978

[Variations in the membrane potentials of motor neurons during the generation of scratching].

The activity of motoneurons of the ankle flexor and extensor muscles was recorded intracellularly during fictitious scratching in decerebrate curarized cats. Before the beginning of rhythmical oscillation a large depolarization and tonic discharge were observed in flexor motoneurons, while the membrane potential of extensor ones did not change. When the rhythmical generation began, a short periodic hyperpolarization and corresponding pause in the discharge lasting for the extensor phase of the cycle appeared in flexor motoneurons. In extensor motoneurons a periodic depolarization increasing in the course of the flexor phase was observed; a maximal depolarization occurred in the extensor phase in which a short burst of spikes was generated.

Animals↗
PubMed1978

[Modulation of Renshaw cell activity during scratching].

The activity of the Renshaw cells was recorded during fictitious scratching in 7 decerebrated and 1 spinal curarized cats. The flexor and extensor Renshaw cells were identified according to the responses induced by orthodromic stimulation of muscle nerves. Before the beginning of rhythmical oscillations, the background activity of the flexor Renshaw cells was inhibited. When the rhythmical generation began, both flexor and and extensor cells generated short bursts of spikes at the end of the flexor phase and at the extensor phase of the cycle. The activity of flexor cells began and terminated earlier in the cycle than that of the extensor cells. The results show that the flexor Renshaw cells are active reciprocally with flexor motoneurons, while the extensor cells are coactivated with extensor motoneurons.

Animals↗
PubMed1977

[Activity of propriospinal neurons in cats during the scratch reflex].

In the thalamic cats immobilized with flaxedil, the tactile stimulation of the pinna evoked fictitious scratching, i.e. rhythmical activity of the hindlimb motoneurons with a pattern of discharge typical of the actual scratching. Activity of propriospinal neurons from the segments C1--C2 and Th4--Th7 was recorded during such scratching. The neurons were identified by the antidromic response to L1 stimulation. Most neurons did not respond to the pinna stimulation, but some neurons did. They were tonically active during fictitious scratching. The neurons from cervical segments responded also to some other peripheral stimuli, but neurons from thoracic segments did not. Their activity could be inhibited by stimulation of the contralateral pinna. A role of propriospinal neurons in the activation of the spinal mechanisms of scratching is discussed.

Animals↗
PubMed1976

[Coordination of the movement of the tube feet and arms of ophiurae during locomotion].

A role of the tube feet is considered for locomotion of ophiura Amphipholis kochii. During stepping, a tube foot sticks to the ground at its front position, and comes unstuck at the end of the step when reaching a certain hind position (relatively the direction of locomotion). Such an organization of the tubefoot mechanisms of stepping simplifies considerably the cooridination of tube feet and arms movements. The tube feet stick to the ground automatically when the arm on which they are located performs motor functions and push or pull the ophiura forwards; on the contrary, the tube feet come unstuck automatically when their arm moves forwards. Thus, the central nervous system is likely not to participate in the coordination of the tube feet and arms movements. It only determines the common direction of stepping for all tube feet, whereas the coordination between the tube feet and arms is achieved because of special properties of the tube feet stepping mechanisms.

Animals↗
PubMed1976

[Types of locomotion in Ophiuroidea].

Locomotor movements of two species of ophiura from the Sea of Japan: Ophiura sarsi vadicola Djakonov and Amphipholis kochii Lütken, were filmed. Ophiura sarsi moves by means of two symmetric pairs of arms which perform rhythmical rowing movements, the fifth arm is passive and directed backwards. Animals of this species do not use tube feet in locomotion. In Amphipholis kochii, three main modes of locomotor movements were found. (1) "Breast stroke" in which two symmetric side arms periodically move forwards, and then push forwards the body and three other arms. In this mode, one arm (leading) is directed forwards, while two others backwards. When the side arms move-forwards or backwards, a wave of successive flexions and extensions propagates along the arm segments. (2) "Pushing" by means of the hind arm and "pulling" with the help of the leading arm. (3) Locomotion by means of the tube feet which perform stepping movements. These three modes of locomotion are observed either separately or in various combinations with each other. In (1) and (2) modes of locomotion the tube feet perform also the coupling of the active arms with the ground which is necessary for the animal movement.

Animals↗
PubMed1976

[Coordination of arm movement during locomotion in Ophiuroidea].

Ophiura Amphipholis kochii Lütken can move with any one of five arms directed forwards; therefore, each arm performs various functions during locomotion. The arm amputated together with the adjoining part of the central nervous ring is capable of complicated behaviour, particularly, of locomotion. Transection of the central nervous ring results in disturbances of the arms coordination. Experiments with amputation of a part of the arms showed that afferent signals from arms are important for determination of the leading arm and mode of locomotion. The experimental data suggest that each arm has an autonomous nervous centre, and coordinated activity of all arms is acheaved by an interaction of the nervous centres. The interaction results in function distribution among the arms and in synchronization of arm movements. The leading arm prevails, since the influences exerting by its centre determine activity of adjacent centres.

Animals↗
PubMedDate not supplied

[Ecological aspects of myasthenia gravis in the Orenburg region].

The paper reflects the problem of adverse environmental factors on human health, including those on the prevalence of myasthenia and on the blood levels of trace elements in the patient. It outlines the environmental status in the Orenburg Region, which is most unfavorable in the Eastern and Central areas. Myasthenia morbidity trends for its increase are covered in 1967 to 2006. The paper also shows the prevalence of myasthenia, with predominance per 100,000 individuals in the Eastern and Central areas, which coincides with the highest anthropogenic load in these areas. The data of a preliminary analysis of trace elements, such as copper, zinc, manganese, nickel, lead, strontium, chromium, cadmium, cobalt, iron, in the blood of patients with myasthenia as compared with those in controls and by regions reflect a general trend for the blood levels of these trace elements to be decreased, as well as their imbalance by the areas of the Orenburg Region.

Catchment Area, Health↗
PubMedDate not supplied

[Description of electromyograms using a mathematical model of single joint movement].

A mathematical model for motor control over one-joint fast and slow movements is proposed based on the equilibrium point (EP) hypothesis. Equations describing a reaction of the muscle with its servo to an EP shift are presented. EMG level is estimated as a function of kinematic and control variables. Voluntary movements are performed by a ramp EP shift for the muscles subserving a given joint. EMG patterns obtained by a computer simulation are in good agreement with the experimental data.

Biomechanical Phenomena↗
PubMedDate not supplied

[A model of control of the movement of the multiarticular extremity].

A model for coordinated execution of multijoint goal-directed limb movements is suggested from the following principles. (1) Central control signals for a single limb joint are individually formed, proceeding from its ability to bring the limb nearer to the target and leaving control signals directed simultaneously to other joint out of account. The joints thereby behave as a set of Tsetlin's abstract automata [11], each functioning independently and guided by a common, collective effect. (2) Neither levels of muscle activation, nor force and kinematic variables are directly specified by the command signals. They only modify the system's parameters that affect equilibrium joint positions, and thus make the limb to move to the goal. A concrete model based on the above principles is described and its behavior is compared with actual goal-directed movements in man and spinal frogs. Various control strategies for multiarticular movements in living organisms are discussed.

Animals↗