Afferent projections to posterior lobe of the cerebellum and their spinal pathways in the cat and in the monkey

The projections to the receiving areas of the posterior cerebellar lobe (the paramedian lobule of the cat and the tonsil of the monkey) have been studied by the evoked potential method following stimulation of skin muscle and articular nerves of the hindleg. By means of acute cord incision an attempt was made to identify the spinal tracts responsible for the conduction of the different impulses. Results emphasize the prominence of cutaneous over muscle afferents and the fact that spinocerebellar pathways are functionally aspecific. The possible tracts involved in the transmission of those impulses are discussed.

Inhibitory action of bulbar and suprabulbar reticular formation on the spinal reflex pathway

Inhibitory action of bulbar and suprabulbar reticular formation on spinal flexor and extensor reflex pathways was studied. In some instances a reciprocal effect was obtained but usually a generalized inhibition resulted. Inhibition varied in magnitude but was always present during reticular formation stimulation. In a high percentage of cases inhibition persisted for a period of 2–3 minutes after cessation of stimulation. Stimulations which blocked the reflex occasionally also had an inhibitory effect on the antidromic potential evoked by stimulation of the motor fibers involved in the reflex but in many instances the antidromic potential was actually augmented. The inhibitory stimulation also did not prevent facilitation of the antidromic potential by orthodromic stimuli. Post-tetanic potentiation was not prevented nor terminated by stimulation of the inhibitory areas of the reticular formation. This data suggest that inhibition from the reticular formation does not block afferent terminals but acts postsynaptically in such a manner, however, as not to increase axon hillock block of antidromic invasion of the soma. Effects of certain anesthetics and drugs on these phenomena were studied.

Intracellular slow potential of dorsal root fibers

Intracellular potential changes associated with excitation were recorded from a dorsal root fiber in the funiculus of an isolated spinal cord of a bullfrog or toad. The spike potential of a dorsal root fiber was observed to follow the slow positive (inside) potential. This slow potential was recorded without a spike potential by applying stimuli sub-threshold for the impaled nerve fiber. The size of the slow potential increased gradually with increased strength of dorsal root stimuli, but with no accompanying prolongation of its declining phase. Dorsal root reflex discharges were occasionally superimposed on this slow potential. No summation of the slow potential resulted from two successive supramaximal stimuli. The slow potential induced by a test stimulus showed considerable occlusion even half a second after the conditioning stimulus. The slow positive (inside) potential was also recorded intracellularly by applying antidromic ventral root stimuli. The slow potential recorded here proved to be generated intrinsically by the depolarization of the surface membrane of the impaled nerve fiber. Active depolarization of the membrane of the terminal endings of the dorsal root fiber may spread out electrotonically along the membrane of the nerve fiber and provide this slow potential. The membrane of terminal endings of a single dorsal root fiber may be depolarized secondarily by the activity of other dorsal root fibers or secondary neurons. The relationship between positive deflection of the cord dorsum potential, the dorsal root potential, and the slow potential recorded intracellularly in this experiment has been analyzed.

Antidromic impulses in the dorsal roots

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Effects of direct current on motor neurones

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