Heiarchal systems

These systems are delimited in their anatomic distribution and generally contain large myelinated, rapidly conducting fibers. Hierarchical systems control major sensory and motor functions. The major excitatory transmitters in these systems are aspartate and glutamate. These systems also include numerous small inhibitory interneurons, which use γ-aminobutyric acid (GABA) or glycine as transmitters. Drugs that affect hierarchical systems often have profound effects on the overall excitability of the CNS.