Observations on the morphology of intracellularly stained gamma-motoneurons in relation to their axon conduction velocity.

Hindlimb gamma-motoneurons of adult cats were stained intracellularly with horseradish peroxidase. The gamma-motor-axons had intramedullary diameters between 2.0 micron and 2.4 micron and lacked recurrent collaterals. The conduction velocity of the gamma-motor-axons (20-29 m/sec) was close to what could be predicted from the relationship between conduction velocity and intramedullary diameter of much thicker adult alpha-motor-axons. However, the gamma-motor-axons were conducting much faster than alpha-motor-axons of 1-week-old kittens in spite of the fact that these two types of axons had about the same dimensions intramedullarly.