basal ganglia
This term refers to a complex system of nuclei rather than a single structure. In medical and anatomical discourse, it is treated as a plural noun because it describes a collection of multiple nuclei (such as the caudate nucleus and putamen).
Because it is a plural-only term in this context, it typically takes a plural verb (e.g., "the basal ganglia are") rather than a singular one. It is rarely used in the singular form "basal ganglion" unless referring to a specific, individual nucleus within the group.
Meanings
A group of subcortical nuclei located deep within the cerebral hemispheres of the brain that are primarily responsible for the regulation of voluntary motor movements, procedural learning, and certain cognitive and emotional functions.
The basal ganglia are heavily implicated in the pathology of Parkinson's disease.