Sensory inputs to neurones in Clarke's column from muscle, cutaneous and joint receptors.

1. Discharge of neurones at the region of Clarke's column of the cat was recorded intracellularly or extracellularly in response to electrical stimulation of various hind limb nerves or to adequate stimuli applied to a variety of sensory receptors.2. According to the type of excitatory sensory input, the neurones were classified into four groups. Their relative proportions were: muscle group, 55-65%; cutaneous group, 15-25%; joint group, 5-15%; convergent group, 10-20%.3. The location of the neurone cell bodies was examined by marking the site of extracellular recording with fast green. The neurones of the muscle or cutaneous group were found to be within Clarke's column. One out of four neurones tested for the joint group and two out of six cells examined for the convergent group were found to be located outside the column.4. There was no difference in axonal conduction velocity among the neurones of different groups.5. The neurones of different groups could be distinguished in terms of the pattern of discharges recorded under ;resting' conditions and during activation of sensory receptors. It is suggested that information carried by dorsal spinocerebellar tract neurones to the cerebellum has a lower signal-to-noise ratio for cutaneous inputs than for muscle or joint inputs.