[The excitation of the fibers of the funiculus dorsalis medullae spinalis during the stimulation of different groups of cutaneous and muscle nerve fibers in the cat].

Abstract

Electric stimulation of various groups of fibres of cutaneous and muscle nerve of cat has been studied for its effect on action potentials in the gray dorsal column fibres, Registration was performed at the level L2--L3 from ipsi- and contralateral dorsal columns, using needle electrodes. Action potentials of dorsal columns, arisen by stimulation of cutaneous nerves, had a more complex form than those of stimulated muscle nerves. Nonmyelinated fibres of a cutaneous nerve are shown to relate to those of dorsal columns. Excitation of high-threshold A- and C-fibres activates the most fast-conducting fibres of dorsal columns. When a stimulus was applied to all fibres of the cutaneous nerve, the action potentials with conduction velocities of 146-0.24 m/s were recorded in dorsal columns. It was shown that such conduction velocities remained in dorsal columns to level C7. Stimulation of muscle nerves excited only myelinic fibres of dorsal columns, the conduction velocities ranging from 90 to 2.3 m/s. By alternating stimulation of either nerve with a 30-300 ms interval we decreased the action potential amplitude of the nerve that was the second to be stimulated. It is likely be related to convergence of the cutaneous and muscle nerve inputs in the spinal cord on the same neurons. A suggestion is made that faster transfer of high-threshold cutaneous signals in dorsal column are associated with the necessity of rapid information about damaging stimulation.