In neuroanatomy, a nucleus is a brain structure consisting of a relatively compact cluster of neurons. It is one of the two most common forms of nerve cell organization, the other being layered structures such as the cerebral cortex or cerebellar cortex. In anatomical sections, a nucleus shows up as a region of gray matter, often bordered by white matter. The vertebrate brain contains hundreds of distinguishable nuclei, varying widely in shape and size. A nucleus may itself have a complex internal structure, with multiple types of neurons arranged in clumps (subnuclei) or layers. In addition, nucleus can refer to an identifiable distinct group of neurons that can spread over an extended area. For example, the reticular nucleus of the thalamus is a thin layer of inhibitory neurons that surround the thalamus.
In the peripheral nervous system, a cluster of neurons is called a ganglion. One exception is the basal ganglia which are located not in the periphery but rather in the forebrain. Ganglia are composed mainly of neuron cell bodies (somata) and dendritic structures. They are the intermediary connections between the peripheral and central nervous systems.
Innervation of the Autonomic Nervous System
Satellite glial cells are expressed throughout the sympathetic and parasympathetic ganglia in their respective nervous system divisions.
Satellite glial cells are a type of glial cell that line the exterior surface of neurons in the peripheral nervous system (PNS) . Satellite glial cells (SGCs) also surround neuron cell bodies within ganglia. They are of a similar embryological origin to Schwann cells of the PNS, as they are both derived from the neural crest of the embryo during development. SGCs have been found to hold a variety of roles, including control over the microenvironment of sympathetic ganglia. They are thought to have a similar role to astrocytes in the central nervous system (CNS). They supply nutrients to the surrounding neurons and also have some structural function. Satellite cells also act as protective, cushioning cells. Additionally, they express a variety of receptors that allow for a range of interactions with neuroactive chemicals.