Biomedical subjects

Y Gerasimenko

Publications and source records attributed to Y Gerasimenko.

4 recordsLinked to original sources

PubMed1998

Evidence for a spinal central pattern generator in humans.

Non-patterned electrical stimulation of the posterior structures of the lumbar spinal cord in subjects with complete, long-standing spinal cord injury, can induce patterned, locomotor-like activity. We show that epidural spinal cord stimulation can elicit step-like EMG activity and locomotor synergies in paraplegic subjects. An electrical train of stimuli applied over the second lumbar segment with a frequency of 25 to 60 Hz and an amplitude of 5-9 V was effective in inducing rhythmic, alternating stance and swing phases of the lower limbs. This finding suggests that spinal circuitry in humans has the capability of generating locomotor-like activity even when isolated from brain control, and that externally controlled sustained electrical stimulation of the spinal cord can replace the tonic drive generated by the brain.

Action Potentials↗

PubMed1992

The effect of muscle fiber length change on motor units potentials propagation velocity.

The influence of the muscle length on the propagation velocity of the extraterritorial action potentials was studied. Single low--threshold motor units (MUs) from m. biceps brachii, both with superficially and deeply situated fibers were investigated. The velocity of excitation propagation decreases with the muscle elongation. This dependence is not so prominent for MUs having more deeply situated fibers. In case of superficial MUs the experimentally obtained values are in better agreement with the core conductor model (v = k.square root of r), than with the linear dependence of the propagation velocity (v) on the muscle fiber radius (r) (v = k.r) observed by Håkansson (1957) on frog muscles. The observed difference between superficial and deep MUs was discussed. At least two factors may be responsible for greater changes of the excitation propagation velocity along the fibers of the superficially situated MUs during the muscle elongation. One possible factor is the essential change in the external resistance due to the decrease of distance from the fibers to the skin surface. The greater change of the muscle length during a passive muscle stretching might be another reason.

Action Potentials↗

PubMedDate not supplied

Relation between the motor units recruitment threshold and their potentials propagation velocity at isometric activity.

The relationship between the propagation velocity of the excitation along the muscle fibers of the motor units (MUs) and their threshold of recruitment at different level of isometric voluntary contraction was investigated. The threshold of recruitment was measured by the value of the muscle force, expressed in percents from the maximal voluntary contraction (MVC) at which the first impulse of the MU appeared. A wire subcutaneous branched electrode was used to select the potentials from a single MU. The selected in this way MU impulses were used as a trigger to average two electromyographic (EMG) signals picked up by means of two monopolar surface electrodes with small leading-off areas mounted on a common plate at a distance of 10 mm from one another. The propagation velocity of the extraterritorial potentials of the MUs increased non-linearly with the increase of the recruitment threshold. The relationship was fitted as V = square root of a+b.theta, where v is the propagation velocity, theta is the threshold of recruitment and a and b are constants. The consideration of the velocity of propagation as a "size principle parameter" was discussed and the limitations of the latter are pointed out.

Action Potentials↗

PubMedDate not supplied

Influence of the interimpulse interval on the propagation velocity of the motor unit potentials.

The influence of the rate of firing of separate human motor units (MUs) from m. biceps brachii on the propagation velocity of the extraterritorial MU potentials was investigated. The experiments were carried out under normal physiological conditions--different level of isometric voluntary activity and different rate of firing--respectively. The subjects succeeded to keep 3-5 different levels of relatively constant rate of firing with mean value of the interimpulse intervals ranging from 67.8 to 183.2 ms. Wire subcutaneous branched electrodes and conventional bipolar wire electrodes were used to separate potentials from single motor units and as a trigger to average surface electromyographic (EMG) signals. MUs with superficially and deep lying muscle fibers were investigated. The propagation velocity of the potentials of superficially lying MUs was calculated from the time shift between the EMG signals picked up by means of two monopolar surface electrodes placed along the direction of the muscle fibers. For deep lying MUs the changes in the propagation velocity were estimated indirectly by the changes in the duration of the extraterritorial MU potentials. No systematic relationship between the rate of firing and the velocity of propagation was found.

Action Potentials↗