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Biomedical subjects

N Tankov

Publications and source records attributed to N Tankov.

At least 19 recordsLinked to original sources
PubMed1991

Postural adjustments upon arm movement during sinusoidal induced body oscillations.

Postural adjustments due to the fast forward right arm elevation, performed during sinusoidal induced body oscillations in the phase of platform-induced dorsal, as well as plantar flexion of the foot were studied. Start times of the changes in the cyclic way of the center-of-gravity position (SG) and right ankle goniogram (GG) as well as the EMG onsets of the right soleus (S), anterior tibial (AT) and femoral biceps (FB) muscles relative to the ipsilateral anterior deltoid muscle (AD) EMG onset were measured. The EMG onset of FB muscle was found to occur significantly before the EMG onset of the AD muscle during plantar flexion series, wherever during dorsal flexion series the EMG onset of the AT muscle was significantly before the AD muscle EMG onset. Only the FB muscle changed significantly its EMG onset with the change of platform direction and started later in the dorsal flexion series. The results showed that two different strategies of postural adjustments might be distinguished depending on the direction of the platform movement.

Adult↗
PubMed1987

Postural adjustments associated with a fast voluntary arm movement at various foot positions.

The aim of the study was to further investigate postural adjustments associated with a fast voluntary arm elevation at various foot positions. The subjects stood upright on a force platform and participated in 3 sessions according to foot position: horizontal position, dorsal and plantar flexion of 6 degrees. EMG activity of anterior deltoid muscle (DA) and of ipsilateral and contralateral soleus (SD, SS), biceps femoris (BFd, BFs) and ipsilateral anterior tibial (TAd) muscles, initial acceleration (Acc) and stabilogram change (Sg) were recorded. The results showed that postural preadjustment was provided by a co-contraction of SOLd and TAd, preceding 31-37 ms the time onset of DA, observed in all foot positions. Time onset of EMG activity in BFd and BFs followed 105-134 ms after EMG onset of DA, showing some dependence on foot position. The co-contraction of SD and TAd presumably has postural function with the role to maintain stability of the body against the increased postural requirements associated with a very fast arm movement. The preceding activity of BFd and BFs and their participation in postural preadjustments is probably not necessary, since the co-contraction of SD and TAd has ensured fixation of the ankle joint.

Adult↗
PubMed1986

Motor unit activity during different functional states of the neuromuscular system.

The study showed that the mean interspike interval (ISI) and the variability of ISIs increased with fatigue for both low and high threshold motor units (MUs). The recruitment threshold tension decreased for both the low and high threshold MUs while the recruitment threshold in % of maximal voluntary contraction changed selectively because of decrease of muscle force. During ischaemia after an initial decrease of mean ISI and ISIs' variability there was an essential increase of variability of ISIs at almost the same mean ISI followed by a considerable final increase of both parameters. MUs' recruitment thresholds lowered with ischaemia more rapidly in the beginning and especially in the final stage of ischaemia.

Action Potentials↗
PubMed1981

Pattern of group I fibre projections from ankle flexor and extensor muscles in man.

Variations in the H-reflex of soleus, tibialis anterior, quadriceps and short head of biceps femoris muscles were studied in normal man, preceded by a conditioning stimulus applied to either gastrocnemius medialis, the inferior branch of soleus or the common peroneal nerve. The observed variations were evoked by low threshold afferents, had a very short latency suggesting oligosynaptic linkage and disappeared during a selective ischaemic blockade of group I fibres; they were therefore regarded as due to group I fibre stimulation. Biphasic variations were observed in almost all cases: evidence is presented that the early low threshold effects, facilitatory for synergistic and inhibitory for antagonistic motoneurone pools, are due to stimulation of Ia fibres, while the subsequent opposite effects which had a slightly higher threshold are Ib in origin. Even though the pattern of projections of group I fibres from ankle flexors and extensors is qualitatively the same in normal man as in the spinal cat, large quantitative differences are observed; in normal man the effects of group I fibres from ankle flexors and extensors upon close synergistic and direct antagonistic motoneurone pools are weak, and often negligible, whereas they are extremely potent upon quadriceps motoneurones.

Adult↗
PubMed1980

Glycogen depletion of bag1 fibers elicited by stimulation of static gamma axons in cat peroneus brevis muscle spindles.

1. The distribution of static fusimotor axons to intrafusal muscle fibres in cat peroneus brevis spindles has been studied with the glycogen depletion method. 2. In each of six experiments three to seven static axons were stimulated. The muscle was subsequently quick-frozen and cut in serial transverse sections that were stained for glycogen. In each muscle, nearly all the spindles were examined for depletion. 3. Intrafusal muscle fibres displaying zones of complete glycogen depletion were observed in fifty-two whole spindles and seven half-spindles. Chain fibres were depleted in forty-eight (92%) of the whole spindles, bag2 fibres in thirty-five spindles (67%) and bag1 fibres in nineteen spindles (36%). 4. Seven other experiments were performed to test whether small amplitude sinusoidal stretching (30--100 Hz) of the muscle might produce glycogen depletion in bag1 fibres. Two hundred and seven spindles were examined. In nearly all of them the glycogen content of the intrafusal muscle fibres was normal. Two muscles had limited atrophic portions within which a few depleted spindles were found. 5. These experiments show that the intrafusal distribution of static gamma axons is not restricted to chain and bag2 fibres but that in a significant number of spindles the bag1 fibres are also supplied by static gamma axons.

Animals↗
PubMed1977

Motor units activity of dog postural muscles in standing position.

Discharges of separate motor units (MU) of dog muscles are studied in standing position and under conditions of passive stretch and shortening of the muscles. In standing position the average discharge frequency in the fore leg extensors is found to be of the order of 25-30 imp/s. A doublet pattern of firing and recruitment and derecruitment of single MUs over different periods of time is observed. The transient processes of the instantaneous discharge frequency of single MUs are observed upon passive stretch and shortening of the muscles. Different types of transient processes are described, both during recruitment and derecruitment in standing-position, and during the passive changes in muscle length. A dependence is found of the transient processes in the velocity of the passive changes in length and the probably physiological mechanisms of these phenomena are discussed.

Animals↗
PubMed1977

Significance of different feedbacks for the transient processes of the discharges of single motor units during step-like voluntary movements.

Studies are made of the transient processes of the discharges of single tonic low-threshold and phasic high-threshold motor units (MUs) during step-like voluntary movements performed in case of visual feedback by the result of the movement and in case of artificial auditory feedback by the sound of the MU impulses, as well as in cases of absence of exteroceptive feedback. The studies comprise isometric and isotonic flexion and extension in the elbow joint, the MUs studied being from m. biceps brachii. The previously observed differences of the transient processes in tonic and phasic MUs are found to exist not only during movements taking place under visual control but also under other conditions studied. Under conditions of articicial auditory feedback the subjects may or may not use this feedback for control of the motor response.

Adult↗
PubMed1977

Firing of motor units upon flexion reflex in dogs.

A study is made of the changes in the transient processes of the instantaneous frequency of the discharges of preactive motor units (MU) in dog m. gastrocnemius and m. semitendinosus under conditions of flexion reflex caused by electrical stimulation. Surface electrodes are used to record the activity of the single MUs. Five types of transient processes are described mainly depending on the intensity of stimulation. A stimulus with weaker intensity leads to an increase in the instantaneous frequency of the discharges 60 ms after its application, followed by a decrease and later by a new increase. Inhibition phenomena are observed in cases of higher intensity. The interpretation of these data takes into consideration the mechanisms of recurrent inhibition and the role of some of the afferent inputs of the flexion reflex.

Animals↗