Ultimately this imbalance between inhibitory and excitatory activities leads to the manifestation of typical clinical symptoms that include resting tremor, rigidity, postural instability, and slowed movement.
Now, as you may know, the binding of glutamate to the NMDA receptor results in an influx of extracellular calcium, which controls membrane excitability and synaptic transmission.
Now, these signals can be either excitatory, which is that they raise the likelihood the neuron will fire, or inhibitory in that they lower the likelihood that the neuron will fire.