Synaptic transmission of proprioceptive and cutaneous impulses through the cuneate nucleus

Summary

• 1. Responses of 100 neurons of the cuneate nucleus to stimulation of cutaneous and proprioceptive afferents of the ipsilateral forelimb were investigated.

• 2. From analysis of the latent periods of responses of these cells they can be divided into two groups: one with latencies from 3.5 to 6.5 msec, and a second with latencies from 7 to 18.3 msec. These two groups can be regarded as activated monoand polysynaptically by peripheral nerve stimulation. The great majority of cells of the first group lie at depths of between 0.8 and 1.2 mm, the great majority of cells of the second group at depths of between 1.2 and 1.6 mm from the dorsal surface of the nucleus.

• 3. The number of cells activated monosynaptically during stimulation of cutaneous afferents is much greater than the number activated monosynaptically by stimulation of proprioceptive afferents.

• 4. A characteristic feature of responses of cells connected with cutaneous afferents is their ability to respond by grouped discharges to single afferent impulses. Cells connected with proprioceptive afferents, on the other hand, respond to a single impulse by one, or sometimes two, action potentials.

• 5. A group of cells has been found which is activated during stimulation of both cutaneous and proprioceptive afferents with approximately the same latency. These cells are distributed diffusely throughout the depth of the nucleus.