R.S. Snider, H.W. Magoun and W.S. McCulloch
In cats and monkeys excitation of (1) the tactile projection areas of cerebellar cortex (near vermian vein of anterior lobe and anterior folia of paramedian lobule), of (2) fastigial nucleus, of (3) bulbar reticular formation or of (4) its descending fibers in the angle of the pyramidal decussation suppresses motor response to cortical stimulation, diminishes tendon reflexes and relaxes decorticate or decerebrate rigidity. With electrical recording, impulses from the first structure reach the third after three milliseconds, whereas those from the second, after approximately one millisecond. This system is predominantly ipsilateral in its action.
Deep reflexes and tonus are enhanced by destruction of the enumerated structures, each of which is necessary for the aforesaid functions of all above it. The suppressor action of the fastigial nucleus is not maintained in the absence of the cerebellar cortex, nor is that of the bulbar reticular formation in the absence of cerebellar and cerebral projections to it.
Hence, from Purkinje cells of cortex of anterior lobe and paramedian lobule of cerebellum, impulses pass to the fastigial nucleus whence they are relayed to the bulbar reticular suppressor mechanism and thence, relayed by cells whose axons pass through the pyramidal angle down the ventrolateral fasiculi of the cord, prevent response of anterior horn cells to cortical, tonic and reflex excitation.
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Keywords: Pathway, Lobe, Nucleus, Cortex, Lobules, Formation, Decussation, Lobule, Stimulation, Response
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