The aim of this paper is to describe the connectivity of some basic neuronal circuits assumed to be causally related to the generation of symptoms in schizophrenia. The role of various transmitter substances like dopamine, glutamate, serotonin and GABA can be explained by the circuitry of the respective pathways in the brain. Activating and inhibiting loops that are coupled can shift into an imbalance that might result in the generation of positive and negative symptoms. Finally, the paper draws attention to the hypothesis that extrasynaptic receptors might play an important role in schizophrenia. The paper shows that thinking in loops might be an efficient strategy for obtaining a functional understanding of the neuronal circuitry involved in the complex symptomatology of schizophrenia. Those models help us to understand the action of antipsychotic medications.