In
neuroanatomyNeuroanatomy is the study of the anatomy and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems, and thus we can begin to speak of...
, a
nucleus is a
brainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
structure consisting of a relatively compact cluster of
neuronA neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s. It is one of the two most common forms of nerve cell organization, the other being layered structures such as the
cerebral cortexThe cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
or
cerebellar cortexThe cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
. In anatomical sections, a nucleus shows up as a region of
gray matter"Gray Matter" is a short story by Stephen King, first published in the October 1973 issue of Cavalier magazine, and later collected in King's 1978 collection Night Shift. It is set in the same area as King's novel Dreamcatcher.-Setting:...
, often bordered by
white matterWhite matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
. The
vertebrateVertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
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.
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
reticular nucleus of the thalamus, for example, is a thin layer of inhibitory neurons that surrounds the thalamus.
Some of the major anatomical components of the brain are organized as clusters of interconnected nuclei. Notable among these are the
thalamusThe thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
and
hypothalamusThe Hypothalamus is a portion of the brain that contains a number of small nuclei with a variety of functions...
, each of which contains several dozen distinguishable substructures. The
medullaThe medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...
and
ponsThe pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...
also contain numerous small nuclei with a wide variety of sensory, motor, and regulatory functions.
In the
peripheral nervous systemThe peripheral nervous system consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system to the limbs and organs. Unlike the CNS, the PNS is not protected by the bone of spine and skull, or by the blood–brain...
, a cluster of neurons is referred to instead as a
ganglionIn anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
.
Examples
- Brainstem: red nucleus
The red nucleus is a structure in the rostral midbrain involved in motor coordination. It comprises a caudal magnocellular and a rostral parvocellular part.-Function:...
, vestibular nucleus, inferior olive
- Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
: dentate nucleusThe dentate nucleus is located within the deep white matter of each cerebellar hemisphere, and it is the largest single structure linking the cerebellum to the rest of the brain. It is the largest and most lateral, or farthest from the midline, of the four pairs of deep cerebellar nuclei, the...
, emboliform nucleusThe emboliform nucleus lies immediately to the medial side of the nucleus dentatus, and partly covering its hilus. It is one among the four pairs of cerebellar nuclei, which are from lateral to medial: the dentate, interposed , and fastigial nuclei...
, globose nucleusThe globose nucleus is one of the deep cerebellar nuclei. It is located medial to the emboliform nucleus and lateral to the fastigial nucleus. This nucleus contains primarily large and small multipolar neurons....
, fastigial nucleusThe fastigial nucleus or nucleus fastigii refers specifically to the concentration of gray matter nearest to the middle line at the anterior end of the superior vermis, and immediately over the roof of the fourth ventricle, from which it is separated by a thin layer of white matter...
- Basal ganglia
The basal ganglia are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas...
: striatumThe striatum, also known as the neostriatum or striate nucleus, is a subcortical part of the forebrain. It is the major input station of the basal ganglia system. The striatum, in turn, gets input from the cerebral cortex...
(caudateCaudate can refer to:* Caudate nucleus* Caudate lobe of liver* Cauda equina* Members of the Caudata order....
and putamenThe putamen is a round structure located at the base of the forebrain . The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that comprises the basal ganglia. Through various pathways, the putamen is connected to the substantia nigra and globus pallidus...
), pallidum (globus pallidusThe globus pallidus also known as paleostriatum, is a sub-cortical structure of the brain. Topographically, it is part of the telencephalon, but retains close functional ties with the subthalamus - both of which are part of the extrapyramidal motor system...
, medial and lateral), substantia nigraThe substantia nigra is a brain structure located in the mesencephalon that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", as parts of the substantia nigra appear darker than neighboring areas due to high levels of melanin in...
, subthalamic nucleusThe subthalamic nucleus is a small lens-shaped nucleus in the brain where it is, from a functional point of view, part of the basal ganglia system. Anatomically, it is the major part of subthalamus. As suggested by its name, the subthalamic nucleus is located ventral to the thalamus. It is also...
- Cranial nerve nuclei