[Central program for activation of hindlimb muscles during scratching in cats]

Electrical activity in nerves of different hindlimb muscles was investigated during fictitious scratching in decerebrated and decapitated cats. Phases of motor discharges could be distinguished corresponding to the phases of real scratching: aiming (flexion in the thigh and ankle joints and extension in the knee joint) and scratching (opposite movements in the same joints). According to the pattern of the discharges the hindlimb muscles were divided into three groups. In the nerves to the muscles of the 1st group the activity was observed during "initial aiming" period and during rhythmic "aiming phases". It was reciprocal to the activity in the nerves to the muscles of the 2nd group appearing during "scratching phases". In the nerves to the muscles of the 3d group the activity was observed both in "initial aiming" period and in rhythmic "aiming and scratching phases". Passive forward deflexion of the limb intensified the "scratching phases" and decreased the intensity of the discharges during "initial aiming" and "aiming phases". Physiological significance of such an organization of central program and structure of spinal scratching generator are discussed.