ORIGIN, CONDUCTION AND TERMINATION OF IMPULSES IN THE DORSAL SPINO-CEREBELLAR TRACT OF CATS

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Abstract
Electrical activity is initiated in the dorsal-spino-cerebellar (Flechsig''s) tract of the cat by afferent stimulation of the homolateral nerves to muscles of the hind limb, but not by stimulation of the saphenous nerve or of contralateral nerves. The tract begins as low as the 4th lumbar segment and extends into the vermis of the cerebellum where the fibers are distributed bilaterally to the lobulus centralis and to the rostral part of the culmen. A maximal afferent stimulus causes a volley of activity in Flechsig''s tract which lasts up to 10 msec. The early part of the volley arises from stimulation of Clarke''s cells by collaterals from the primary neurons, the cells responding after a synaptic delay of 0.5-0.9 msec. Collaterals from more than one primary neuron may stimulate one cell. Reexcitation of the nucleus by internuncial chains of various length contributes to the later tract activity. Clarke''s cells respond to repetitive synaptic stimulation at a frequency above 500/sec. The responses of the tract fibers, as recorded with micro-electrodes, are spikes lasting 0.5 msec. Impulses ascend in Flechsig''s tract with velocities up to 160 mps. and arrive at the medulla more than one msec. ahead of those which ascend in the fasciculus gracilis. The 1st electrical activity in the cerebellum is that of impulses afferent in Flechsig''s tract. These impulses alone initiate considerable cerebellar activity but additional activity is produced by impulses arriving later via other pathways.