[Functional characteristics and topography of spinal tracts involved in low- and high-threshold startle reflexes].

Electrophysiological and topographical properties of the spinal tract systems involved in two functional types of startle reflexes were studied in chloralose anesthetized cats: a high threshold reflex evoked by intense peripheral nerve stimulation (spino-bulbo-spinal, SBS, reflex) and low threshold evoked by tactile (T-reflex) and acoustic (A-reflex) stimulation. It was found that the mean maximal conduction velocity of descending transmission of SBS-reflexes was much less (30 m/s) than that of T- (85 m/s) and A-reflexes (100 m/s). Ascending conduction velocities for SBS- and T-reflexes were 70.8 and 40.2 m/s, respectively. It was established by partial spinal cord lesions that ascending tracts for T-reflex passed in dorsal and dorso-lateral funiculi; those for SBS reflexes were found not only in the latter but also in ventro-lateral and partially in ventral funiculi. Descending pathways for SBS reflex passed mainly in ventro-lateral funiculi and partially in the ventral ones. Descending pathways of T- and A-reflexes had a similar organization and were located mainly in the ventral and ventro-lateral funiculi. Functional organization of spinal tracts of all studied types of startle reflexes is discussed.