Clinical meaning
Mental health conditions are fundamentally linked to neurotransmitter dysregulation within the central nervous system. Serotonin (5-HT), synthesized from tryptophan in the raphe nuclei, modulates mood, sleep, appetite, and impulse control — deficiency is implicated in depression, anxiety, and obsessive-compulsive disorder. Dopamine pathways include the mesolimbic (reward and motivation), mesocortical (executive function), nigrostriatal (motor control), and tuberoinfundibular (prolactin regulation) systems — dysfunction in these pathways underlies conditions ranging from schizophrenia (mesolimbic hyperactivity) to Parkinson's disease (nigrostriatal degeneration). Norepinephrine, produced in the locus coeruleus, regulates alertness, attention, and the stress response — its dysregulation contributes to attention deficit disorder, anxiety, and depression.