MODULE 7
THE NEW ANATOMY
- - You now have a pretty good understanding of the anatomy of the basal ganglia, but you must be dying for an answer to the question "What do they do?". It has been known for more than a hundred years that damage to to the nuclei of the basal ganglia causes an array of movement disorders. Some of these syndromes are characterized by excessive spontaneous movements, and others are associated with a paucity of movement. In the beginning, clinicians were convinced that the pyramidal tract was NOT involved in the generation of the motor abnormalities, and so they were attributed to the activity of an "extrapyramidal" motor system. Still, the mechanisms involved remained unknown until a few decades ago. As we learned more about the activity of neurotransmitters and as it became possible to record the activity of individual nerve cells, answers to the puzzle have been coming in at a rapid pace. Just as motor activity is refined by a neural "loop" that originates in the cerebral hemisphere, descends to pass through the cerebellum and then returns to the cerebral cortex, so there are similar loops involving the basal ganglia. The best studied of these loops or channels is the motor one, so start by reading about it (Blumenfeld page 702 or Fitzgerald page 358 or Haines page 421). All three texts describe the interaction between direct and indirect pathways through the basal ganglia. Once you master this complex story, go on to get some idea of the additional loops that act in parallel with the motor one.
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