抄録
The afferent impulses from labyrinth are conducted to the medulla through the 8 th cranial nerve and they evoke the efferent impulses which cause contractions of the ipsilateral and contralateral neck muscles. The present authors studied on the central delay in this reflex, namely the labyrinthine reflex on toad (Bufo uulgaris) . The electrical stimulus was given directly both on the 8 th nerve and on the ventral root which innervates the neck muscles. And the action potential was recorded from these neck muscles. The time delay of these records gave the central delay at the medulla. The data obtained are summarized as follows.
1) The central delay in the ipsilateral reflex is shorter than that in the contralateral reflex.
2) The action potential of neck muscle, which is evoked in the 8 th nerve orefiex, is separated into tws waves, but when the stimulus is given on the 3 rd thoracic nerve, the potential wave of that muscle does not separate. This facts indicate that there are in two ways the central path of the medula, which conducts impulses from the 8 th nerve to neck muscle.
3) The central delay is due to the synaptic delay in the medulla, and if the conduction time of one synapse is assumed as 1 msec, the number of synapses corresponds to that of synaptic time, counted by msec.
4) The number of internuntial neurons which connect the 8 th nerve and M. latissimus dorsi, measured as above mentioned way, are 14 and 26 in ipsilateral, 5 and 19 in contralateral. The number of internuntial neurons for M. depressor mandibulae are 5 and 19 in ipsilateral, 7 and 24 in contralateral.
