THE ELECTRO-SALTATORY TRANSMISSION OF NERVOUS IMPULSE
MODEL EXPERIMENTS AND THEORETICAL CONSIDERATIONS
1951 年 2 巻 p. 79-92
詳細
1951 年 2 巻 p. 79-92
Modifying Lillie's nerve model, a model for the medullated nerve fibre was constructed, on which the conduction time for the whole length (40cm.) was measured under various “internodal” distances. The important results obtained were that 1) the conduction velocity gets generally larger in comparison to that of a continuous linear model corresponding to a non-medullated nerve fibre, 2) the velocity attains a maximum at a certain internodal distance (of course the transmission cannot take place if the internodal distance is too large.), and 3) the distance travelled by an activation wave is generally smaller in the case of saltatory transmission than in the case of continuous conduction. The optimal internodal distance, S0, which makes the conduction velocity maximal, was shown mathematically to be
S04/3 rm/r
where r and rM are the axonal resistance per cm. and the transverse resistance of a nodal membrane respectively. It was compared to the actual internodal distance, s, of toad's motor merve fibres, where it is said thatS=3/4 rm/r and discussions were made in connection with the conduction velolcities of the fibres with normal and abnormal internodal distances. Further, it was shown mathematically that S0 and the conduction velocity should both vary proportionally to the fibre diameter. These were supposed to provide us, very probably, with theoretical basis for the two established facts that the actual internodal distance and the conduction velocity are both approximately proportional to the fibre size.
It was argued further that the rhéobase of medullated nerve fibres measured by applying a voltage to two pools of Ringer's fluid, each containing a node of Ranvier separated properly after Tasaki's principle, should be invariable despite the variable fibre size
Finally it was discussed 1) that the hypothesis of the electro-saltatory transmission is probably right, although in a somewhat modified sense, and 2) that the greatest objection raised against it-the existense of medullated nerve fibres without nodes but with a large conduction velocity in the central nervous system-cannot alwaysbe an objection.
