Summation of excitation and inhibition in a second order sensory neuron investigated by computer simulation.

Dorsal spinocerebellar tract (DSCT) neurones adequately activated by primary afferents from the muscle spindles in one muscle in the hindleg of the cat, is regularly inhibited by primary afferents from other muscles. The inhibitory input causes a constant reduction in firing frequency independent of the excitatory drive of the cell. In a simple model the effects of presynaptic inhibition and of postsynaptic inhibition with different time course of the inhibitory action, have been explored. Within the scope of this model, only postsynaptic inhibition with a very long time-constant could explain the experimental results. It is suggested that the inhibitory action is transmitted to the DSCT-cell through a number of synapses distributed over the dendrites.