Changes in the functional state of spinal-cord cell structures under gravitational unloading

Specific Features of the Motor Potentials of the Leg Muscles Induced by Magnetic Stimulation under the Conditions of a Five-Day “Dry” Immersion in Healthy Volunteers

“…In studies carried out during and after the completion of space flights (SF) [1][2][3][4], as well as in experiments simulating the effects of weightlessness on Earth [5][6][7][8][9][10], and in experiments on animals [11][12][13][14], it has been shown that that a decrease in the gravitational load is naturally accompanied by disturbances in the activity of all components and structures of the locomotor apparatus, which together make up the picture of the syndrome of "gravitational ataxia" and "hypogravitational muscle detraining" [15][16][17][18]. According to the literature, the rapid development of atony, ataxia, a decrease in the speed-strength properties of muscles and other components of the "motor syndrome" during the transition to microgravity also testifies to its reflex nature [16].…”

“…It can be assumed that the tendency to a decrease in the amplitude of reflex responses is the result of the influence of a peripheral factor, namely, pronounced muscle atony [2,6]. Some authors explain the increase in the reflex excitability of motor neurons in the soleus and gastrocnemius muscles of rats during gravitational unloading by a decrease in the size of the neuron soma and a transformation of the level of presynaptic inhibition [12] or the development of so-called denervationlike supersensitivity, which causes an increase in reflex activity [14]. † Deceased.…”