The dorsal column projection of muscle afferent fibres from the cat hindlimb.

1. The extent of the projection of hindlimb muscle afferent fibres ascending the dorsal columns has been studied in barbiturate-anaesthetized cats. This has been investigated using electrical stimulation of the dorsal columns at different spinal levels while recording from (i) peripheral muscle nerves, and (ii) single muscle afferent fibres within the dorsal columns. These two approaches have produced complementary results. 2. The conduction velocity of both group I and group II afferent fibres decreased progressively after entering the dorsal columns. 3. The majority of group I and group II fibres project at least as far as L2 but leave the dorsal columns at or before the lower thoracic segments. 4. By taking advantage of the lower electrical threshold of Ia compared to Ib fibres in the hamstring nerves, it could be shown that both Ia and Ib fibres leave the dorsal columns at similar locations. 5. A small number of afferent fibres were found to project to C1. On the basis of previous work it is likely that such fibres originate from Pacinian or paciniform corpuscles.