: nuclei) is a cluster of neurons in the central nervous system,[1] located deep within the cerebral hemispheres and brainstem.
A nucleus may itself have a complex internal structure, with multiple types of neurons arranged in clumps (subnuclei) or layers.
The term "nucleus" is in some cases used rather loosely, to mean simply an identifiably distinct group of neurons, even if they are spread over an extended area.
The medulla and pons also contain numerous small nuclei with a wide variety of sensory, motor, and regulatory functions.
In the peripheral nervous system (PNS), a cluster of cell bodies of neurons (homologous to a CNS nucleus) is called a ganglion.