Medical term:

nucleus

[noo´kle-us] (pl. nu´clei) (L.)

1. cell nucleus; a spheroid body within a cell, contained in a double membrane, the nuclear envelope, and containing the chromosomes and one or more nucleoli. The contents are collectively referred to as nucleoplasm. The chromosomes contain deoxyribonucleic acid (DNA), which is the genetic material that codes for the structure of all the proteins of the cell.

2. a mass of gray matter in the central nervous system, especially such a mass marking the central termination of a cranial nerve.

3. in organic chemistry, the combination of atoms forming the central element or basic framework of the molecule of a specific compound or class of compounds.

4. the dense core of an atom, made of protons and neutrons held together by the strong nuclear force. Traveling in orbit around it is a cloud of negatively charged particles called electrons. The number of protons in the atomic nucleus gives a substance its identity as a particular element. Called also atomic nucleus. adj., adj nu´clear.

The nucleus and nucleolus of a cell. From Mahon and Manuselis, 2000.

nucleus ambi´guus the nucleus of origin of motor fibers of the glossopharyngeal, vagus, and accessory nerves in the medulla oblongata.

nucleus an´sae lenticula´ris (nucleus of ansa lenticularis) a collection of neurons in the ansa lenticularis as it curves around the medial edge of the globus pallidus.

arcuate nuclei of medulla oblongata, nu´clei arcua´ti medul´lae oblonga´tae small irregular areas of gray substance on the ventromedial aspect of the pyramid of the medulla oblongata.

atomic nucleus nucleus (def. 3).

basal nuclei (nu´clei basa´les) specific interconnected subcortical masses of gray matter embedded in each cerebral hemisphere and in the upper brainstem, comprising the corpus striatum (caudate and lentiform nuclei), amygdaloid body, claustrum, and external, extreme, and internal capsules. Called also basal ganglia.

caudal olivary nucleus a folded band of gray substance enclosing a white core, which produces the elevation on the medulla oblongata known as the olive.

caudate nucleus (nucleus cauda´tus) an elongated, arched gray mass closely related to the lateral ventricle throughout its entire extent, which, together with the putamen, forms the neostriatum.

nucleus ceru´leus a compact aggregation of pigmented neurons lying below the locus ceruleus.

cochlear nuclei, anterior and posterior the nuclei of termination of sensory fibers of the cochlear nerve (see anatomic Table of Nerves in the Appendices); they partly encircle the inferior cerebellar peduncle at the junction of the medulla oblongata and pons.

dentate nucleus (nucleus denta´tus) the largest of the deep cerebellar nuclei, lying in the white matter of the cerebellum just lateral to the emboliform nucleus.

droplet nuclei small particles of pathogen-containing respiratory secretions expelled into the air by coughing, which are reduced by evaporation to small, dry particles that can remain airborne for long periods; one possible mechanism for transmission of infection from one individual to another.

emboliform nucleus (nucleus embolifor´mis) a small cerebellar nucleus lying between the dentate nucleus and the globose nucleus and contributing to the superior cerebellar peduncles.

fastigial nucleus (nucleus fasti´gii) the most medial of the deep cerebellar nuclei, near the midline in the roof of the fourth ventricle.

globose nucleus (nucleus globo´sus) a cerebellar nucleus lying between the emboliform nucleus and the nucleus fastigii and projecting its fibers via the superior cerebellar peduncle.

intracerebellar nuclei four accumulations of gray matter embedded in the white matter of the cerebellum, comprising the dentate nucleus, emboliform nucleus, nucleus fastigii, and globose nucleus.

lenticular nucleus (lentiform nucleus) the part of the corpus striatum somewhat resembling a biconvex lens, divided into a larger external or lateral part called the putamen and a smaller light colored internal or medial part called the globus pallidus.

motor nucleus any collection of cells in the central nervous system giving origin to a motor nerve.

olivary nucleus a folded band of gray matter that encloses a white core and produces the elevation called the olive on the medulla oblongata; it receives heavy projections from the spinal cord, mesencephalon, and cerebral cortex and projects fibers via the contralateral inferior cerebellar peduncle.

nuclei of origin, nu´clei ori´ginis groups of nerve cells in the central nervous system from which arise the motor, or efferent, fibers of the cranial nerves.

paraventricular nucleus (nucleus paraventricula´ris) a band of cells in the wall of the third ventricle in the supraoptic part of the hypothalamus; many of its cells are neurosecretory in function and project to the neurohypophysis, where they secrete oxytocin (and, to a lesser extent, antidiuretic hormone).

pontine nuclei, nu´clei pon´tis masses of nerve cells scattered throughout the ventral part of the pons, in which the longitudinal fibers of the pons terminate, and whose axons in turn cross to the opposite side and form the middle cerebellar peduncle, which projects fibers to the neocerebellum.

nucleus pro´prius a column of large neurons that extends throughout the posterior horn of the spinal cord.

nucleus pulpo´sus (pulpy nucleus) a semifluid mass of fine white elastic fibers forming the center of an intervertebral disk.

red nucleus (nucleus ru´ber) an oval mass of gray matter (pink in fresh specimens) in the anterior part of the tegmentum and extending into the posterior part of the hypothalamus; it receives fibers from the cerebellum.

sensory nucleus the nucleus of termination of the afferent (sensory) fibers of a peripheral nerve.

supraoptic nucleus (nucleus supraop´ticus) one just above the lateral part of the optic chiasm; many of its cells are neurosecretory in function and project to the neurohypophysis, where they secrete antidiuretic hormone (ADH) and, to a lesser extent, oxytocin; other cells are osmoreceptors that stimulate ADH release in response to increased osmotic pressure.

tegmental nucleus, laterodorsal several nuclear masses of the reticular formations of the pons and midbrain, especially of the latter, where they are in close approximation to the superior cerebellar peduncles.

thoracic nucleus (nucleus thora´cicus) thoracic column.

vestibular nuclei, nu´clei vestibula´res the four cellular masses in the floor of the fourth ventricle: superior (rostral or cranial), lateral, medial, and inferior (caudal) vestibular nuclei; in them are the terminations of the branches of the vestibular nerve (see anatomic Table of Nerves in the Appendices). The nuclei give rise to a widely dispersed special sensory system through projections to motor nuclei in the brain stem and cervical cord, to the cerebellum, and to motor cells throughout the spinal cord; they also have connections that provide for conscious perception of, and autonomic reactions to, labyrinthine stimulation.

nu·cle·us

, pl.

nu·cle·i

(nū'klē-ŭs, nū'klē-ī),

1. In cytology, typically a rounded or oval mass of protoplasm within the cytoplasm of a plant or animal cell; it is surrounded by a nuclear envelope that encloses euchromatin, heterochromatin, and one or more nucleoli, and undergoes mitosis during cell division.
See also: virion. Synonym(s): karyon

2. By extension, because of similar function, the genome of microorganisms (microbes), which is relatively simple in structure, lacks a nuclear envelope or membrane and does not undergo mitosis during replication.
See also: virion. Synonym(s): nucleoid (3)

3. In neuroanatomy, a group of nerve cell bodies in the brain or spinal cord that can be demarcated from neighboring groups on the basis of either differences in cell type or the presence of a surrounding zone of nerve fibers or cell-poor neuropil.

4. Any substance (for example, foreign body, mucus, crystal) around which a urinary or other calculus has formed.

5. The central portion of an atom (composed of protons and neutrons) where most mass and all the positive charge are concentrated.

6. A particle on which a crystal, droplet, or bubble forms.

7. A characteristic arrangement of atoms in a series of molecules; for example, the benzene nucleus is a series of aromatic compounds.

[L. a little nut, the kernel, stone of fruits, the inside of a thing, dim. of nux, nut]

Farlex Partner Medical Dictionary © Farlex 2012

nucleus

(no͞o′klē-əs, nyo͞o′-)

n. pl. nu·clei (-klē-ī′) or nu·cleuses

1. Biology A membrane-bound organelle within a eukaryotic cell that contains most of the cell's genetic material. DNA transcription takes place in the nucleus.

2. Anatomy A group of specialized nerve cells or a localized mass of gray matter in the brain or spinal cord.

3. Physics The positively charged central region of an atom, composed of protons and neutrons, about which negatively charged electrons orbit. Extremely small and dense, the nucleus contains almost all of the mass of an atom.

4. Chemistry A group of atoms bound in a structure, such as a benzene ring, that is resistant to alteration in chemical reactions.

nucleus

Histology
The organelle in a eukaryotic cell which contains the genomic information (DNA), replicative and transcriptional machinery (RNA), and binding proteins needed to copy the genomic information and encode the structural and functional proteins required for cell activity.

Imaging
An MRI term for the core or centre of most atoms, which contains protons (positive charge) and neutrons (no electrical charge). For the common isotope of hydrogen, the nucleus has a single proton.

Neuroanatomy
An aggregate of neuronal cell bodies sharing a common function (e.g., accessory nucleus, caudate nucleus, nucleus ambiguus).

Organic chemistry
The part of a molecule that is the major determinant of its chemical behaviour (e.g., benzene ring, β-lactam ring, cyclopentano-perhydrophenanthrene in steroids).

nu·cle·us

, pl. nucleuses (nū'klē-ŭs, -ĕz)

1. cytology Typically a rounded or oval mass of protoplasm within the cytoplasm of a plant or animal cell; it is surrounded by a nuclear envelope, which encloses euchromatin, heterochromatin, and one or more nucleoli and undergoes mitosis during cell division.
Synonym(s): karyon.

2. By extension, because of similar function, the genome of microorganisms (microbes), which is relatively simple in structure, lacks a nuclear membrane and does not undergo mitosis during replication.
Synonym(s): nucleoid (3) .

3. neuroanatomy a group of nerve cell bodies in the brain or spinal cord that can be demarcated from neighboring groups on the basis of either differences in cell type or the presence of a surrounding zone of nerve fibers or cell-poor neuropil.

4. Any substance (e.g., foreign body, mucus, crystal) around which a urinary or other calculus is formed.

5. The central portion of an atom (composed of protons and neutrons) where most of the mass and all of the positive charge are concentrated.

6. A particle on which a crystal, droplet, or bubble forms.

7. A characteristic arrangement of atoms in a series of molecules; e.g., the benzene nucleus in a series of aromatic compounds.
See also: virion

nucleus

1. Of a body cell, the central structure consisting of the tightly bundled genetic material DNA surrounded by a nuclear membrane.

2. Of an atom, the central core of protons and, except in the case of hydrogen, neutrons which is surrounded by a rapidly moving cloud of electrons, widely separated from it. The forces which bind together the protons and neutrons are immensely powerful and it is these forces which are released in an atomic explosion. From the Latin nucleus , a nut or kernel.

nucleus

an organelle of eukaryotic cells that is bounded by a NUCLEAR MEMBRANE and contains the chromosomes whose genes control the structure of proteins within the cell.
(anatomy) the mass of nerve cell bodies, connected by tracts of nerve fibres, which occur in the vertebrate brain.

Nucleus

The central part of a cell that contains most of its genetic material, including chromosomes and DNA.

Mentioned in: Gene Therapy

nucleus

1. A mass of grey matter composed of nerve cell bodies in any part of the brain or spinal cord and dealing with a common function. 2. Core or central portion of the cell body of a neuron, containing cellular DNA in particular. Plural: nuclei.
abducens nucleus Nucleus of the abducens nerve (sixth cranial nerve) located in the lower part of the pons and whose axons supply the lateral rectus muscle.
accessory oculomotor nucleus See Edinger-Westphal nucleus.
nucleus of the crystalline lens See crystalline lens.
Edinger-Westphal nucleus Part of the oculomotor nucleus, it is situated posterior to the main nucleus and contains the parasympathetic component of the complex. Axons from the Edinger-Westphal pass out along the third (or oculomotor) nerve to synapse in the ciliary ganglion. Postganglionic fibres pass through the short ciliary nerves to the sphincter pupillae and ciliary muscles. The nucleus also receives fibres concerned with accommodation and fibres from the pretectal nucleus dealing with pupil light reflexes. Syn. accessory oculomotor nucleus; accessory parasympathetic nucleus. See pretectal nucleus; pupil light reflex.
lateral nucleus Part of the oculomotor nucleus which supplies, via the oculomotor nerve, all the extraocular muscles except the superior oblique and the lateral rectus muscles.
lateral geniculate nucleus See lateral geniculate body.
oculomotor nucleus This is the nucleus of the oculomotor nerve (third cranial nerve). It is a complex mass of cells located in the midbrain at the level of the superior colliculus and beneath the cerebral aqueduct (of Sylvius) which connects the third and fourth ventricles. It is divided into several subnuclei. See oculomotor nerve; Edinger-Westphal nucleus; Perlia's nucleus; trochlear nucleus.
olivary nucleus See pretectum; pupil light reflex.
Perlia's nucleus Midline part of the oculomotor nucleus. It is rudimentary in man and primates and may provide part of the innervation of the superior rectus muscle.
pretectal nucleus A complex group of nerve cells in the midbrain anterior to the superior colliculi. One of these, the pretectal olivary nucleus, receives retinal inputs via the optic tract and superior brachium and sends axons to both Edinger-Westphal nuclei. It constitutes a centre of the pupil light reflex. Another, the nucleus of the optic tract, may be involved in the control of reflex eye movements. Other fibres from the pretectal nucleus innervate the cornea, the iris, the ciliary muscle and the extraocular muscles (except the lateral rectus and superior oblique muscles), as well as the levator palpebrae muscle.
trochlear nucleus A nucleus of the trochlear nerve (fourth cranial nerve) located at the level of the inferior colliculus and below the posterior end of the oculomotor nerve nucleus, it sends fibres to the contralateral superior oblique muscle.

nu·cle·us

, pl. nucleuses (nū'klē-ŭs, -ĕz)

1. [TA] In cytology, typically a rounded or oval mass of protoplasm within the cytoplasm of a plant or animal cell.

2. By extension, because of similar function, genome of microorganisms (microbes), which is relatively simple in structure, lacks a nuclear envelope or membrane and does not undergo mitosis during replication.
Synonym(s): nucleoid (3) .

3. [TA] In neuroanatomy, group of nerve cell bodies in brain or spinal cord that can be demarcated from neighboring groups on the basis of either differences in cell type or the presence of a surrounding zone of nerve fibers or cell-poor neuropil.

4. Any substance (e.g., foreign body, mucus, crystal) around which a urinary or other calculus has formed.

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