Clusters of nerve cell bodies located outside the central nervous system that serve as relay stations for nerve signals. In invertebrates, ganglia often function as simple brains or local control centers for specific body regions.
From Greek 'ganglion' originally meaning 'knot' or 'swelling,' first applied to nerve clusters in the 18th century. The anatomical use developed as early anatomists noticed these knot-like swellings along nerve pathways in dissected specimens.
Ganglia are like neighborhood processing centers in the nervous system - they handle local decisions so the main brain doesn't get overwhelmed! In some animals like insects, these 'mini-brains' are so sophisticated they can control complex behaviors even when disconnected from the head.
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