A Descending Pathway which is Monosynaptically Excitatory to Motoneurones

Abstract

NEARLY twenty-five years ago, Lloyd¹ described a pathway descending in the ventral part of the spinal cord of the cat which ended directly on lumbosacral motoneurones and which facilitated the monosynaptic reflex. The pathway was shown by Lloyd to originate from neurones of the brain stem and from spinal proprioneurones. He named the pathway the “bulbospinal correlation system”. Since Lloyd's original description, there has been some physiological work which suggests that the brain stem neurones from which this pathway originates may belong either to the reticular formation² or to the vestibular nuclei³ or to both. Recent studies of the mode of termination of the reticulospinal and vestibulospinal tracts, however, offer little support for the presence of more than a few monosynaptic endings on lumbosacral motoneurones from fibres descending in these tracts⁴. The experiments to be described confirm the presence of long descending axons in the ventral part of the spinal cord which monosynaptically excite motoneurones.