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It is true that all of our thoughts and actions are the result of patterns of action potentials. But the electrical action potentials themselveself are not the only occurance responsible for brain function. We must recognize the structural, chemical, biological, environmental, and genetic involvement as well. I have never actually heard of action potentials malfunctioning. I can imagine it would look something like a generated action potential spontaneously ending en route down an axon, or failing to be initiated by a sufficent stimulus. Physiologically I do not know if this could happen, it would require something to be fatally wrong with the cell, or the extracellular environment.

While action potentials malfunctioning may not be a likely cause, the signals which tell the action potentials to occur (or not) are. Neurotransmitters are released from one neuron into the synaptic cleft and received by another. The "correct" transmission of a signal is reliant on the correct neurtransmitter being released, it being released in the right concentration, staying in the synaptic cleft for a certain period of time, and interacting in a specific way with the right receptors. These "normal" functioning of these steps can be affected by genetics/environment/and biology.

Alot of work on schizophrenia has been done through utilizing antipsychotic drugs, and using what we know of their mechanism of action to deduce the possible mechanism of action of the disease. It seems likely that schizophrenia is at least partly caused by a malfunction in the signalling pathway of dopamine. Drugs that block the D2 dopamine receptor aleviate some of the symptoms of schizophrenia. Schizophrenics might be releasing too much dopamine into the synaptic cleft, not reabsorbing it (so that it stays there longer), or have more than the normal amount of receptors for it. The function of D2 is inhibitory, it decreases the likelyhood of an action potential in the post synaptic cell. The over activation of D2 receptors in schizophrenics will directly effect the number, frequency, and patterns of action potentials in the brain. And therefore directly effect behavior, as is seen.

So it is true that in the end the disordered behavior is caused by an alteration of the action potentials. But the malfunction occurs not in the action potentials themselves, but in the means by which they are induced.

While this does not explain the timing of the onset of symptoms if I had to hypothesize, I would say that the environmental influences that occur during childhood, and the environmental stresses that are often exacerbated in adolesence could be responsible for the later onset of symptoms