The recruitment order of gamma-motoneurones in the decerebrate rabbit.

1. The order of firing (i.e. recruitment order) of gastrocnemius medialis gamma-motoneurones to natural stimulation of the limbs has been studied in the precollicular decerebrate rabbit. 2. Recruitment order was not invariable. However, when a fixed order occurred there was a significant tendency for neurones to be recruited in order of increasing axonal conduction velocity. The functional significance of this finding is discussed. 3. In the preparation used, many gamma-motoneurones were spontaneously active. 4. Two types of gamma-motoneurone were distinguished on the basis of their resting discharge characteristics and responses to natural stimulation. 5. A significant correlation between resting discharge frequency and axonal conduction velocity was found for gamma-motoneurones that were predominantly excited by natural stimulation.