The spinocervical tract: Dorsal column linkage, conduction velocity, primary afferent spectrum

Abstract

Microelectrode studies of single units in the spinocervical tract of the cat under barbiturate anesthesia demonstrate a monosynaptic linkage between the spinocervical tract and dorsal column cutaneous afferents at the segmental level of dorsal root entry. The spinocervical tract is substantially independent of the dorsal spinocerebellar tract, at least 75% of units studied terminating in the region of the ipsilateral lateral cervical nucleus. Mean over-all conduction velocity of units in the spinocervical tract is 58.0 m/sec, compared with mean over-all conduction velocity of cutaneous afferents in the dorsal columns providing input to these spinocervical tract units of 38.6 m/sec. The dorsal column input contains the Aα cutaneous component, of which the small-fibered half is most effective in exciting spinocervical tract units. The Aδ component is lacking. The spinocervical tract primary afferent input contains at least all of the A group to the Aδ component. Thus slow-conducting cutaneous primary afferent fibers may project to fast-conducting long pathways. Some functional and clinical aspects of the spinocervical tract and its homologue are discussed.