THE DIFFERENTIATION OF CONDUCTION VELOCITIES OF SLOW TWITCH AND FAST TWITCH MUSCLE MOTOR INNERVATIONS IN KITTENS AND CATS

¹ Physiology Department, King's College, London

The difference in conduction velocity (maximum and mean) of the motor nerve fibres to fast (flexor hallucis longus) and slow (soleus) twitch muscles in adult cats has been verified, and qualitatively similar differences found in adult rabbits and rats. In addition the conduction velocities of motor nerve fibres to flexor digitorum longus, gastrocnemius medialis and tibialis anticus muscles have been measured in adult cats.

Similar measurements (F.H.L. and soleus only), have been made in a series of kittens ranging in age from 8 hr. to 56 days. Although the conduction velocities in the new-born kitten are one-tenth those of the adult, the ratio of the conduction velocities of motor nerve fibres to fast and slow muscles remains approximately constant from birth onwards.

It is concluded that at birth the differentiation of the conduction velocities of the motor nerve fibres to muscles destined to become fast and slow twitch muscles is complete, although at this time the muscles themselves are only beginning to differentiate in terms of contraction times.

Note:

I should like to thank Professor A. J. Buller for his encouragement, Dr. P. Scott and her staff for kindly providing many of the kittens, Miss M. O'Vens for technical help and Mr. G. F. Stonard for his photography.