ORGANIZATION OF ASCENDING TRACTS IN THE SPINAL CORD OF THE DUCK.

Abstract

AbstractDischarges evoked in ascending spinal tracts on stimulation of muscle, skin, and mixed, leg and wing nerves were recorded from dissected fascicles of the cord. The results show that ascending tracts in the bird are organized as in the mammal: (i) dorsal tracts are mono‐ and polysynaptically activated only from ipsilateral nerves; (ii) ventral tracts are monosynaptically activated only from contralateral nerves and polysynaptically activated from both ipsilateral and contralateral nerves. It is concluded that the former tracts are uncrossed and the latter tracts crossed at the spinal level. — Low threshold muscle afferents activate two ascending spinal tracts: one crossed tract related to leg nerves and one uncrossed tract related to wing nerves. There is evidence that the former but not the latter tract is strongly inhibited from skin and high threshold muscle afferents. It is suggested that the crossed tract is homologous to the ventral spino‐cerebellar tract in mammals. The dorsal spinocerebellar tract either does not exist in the duck or has an organization different from that in the mammal.