 The cortical, thalamic, and brain-stem inputs that arrive at the medium spiny neurons show a vast divergence in that each incoming axon forms contacts with many spiny neurons and each spiny neuron receives a vast amount of input from different incoming axons.Since these inputs are glutamatergic they exhibit an excitatory influence on the inhibitory medium spiny neurons.There are also interneurons in the striatum which regulate the excitability of the medium spiny neurons.