nucleus gracilis

nucleus /nu·cle·us/ (noo´kle-us) pl. nu´clei   [L.]

1. the central core of a body or object.

2. cell nucleus; a spheroid body within a cell, consisting of a thin nuclear membrane, organelles, one or more nucleoli, chromatin, linin, and nucleoplasm.

3. a group of nerve cells, usually within the central nervous system, bearing a direct relationship to the fibers of a particular nerve.

4. 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.

5. see atomic n. nu´clear

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

anterior olfactory nucleus  scattered groups of neurons intermingled with the olfactory tract that run caudally from the end of the olfactory bulb, some receiving synaptic stimuli from the fibers of the olfactory tract.

arcuate nucleus 

1. a nucleus of nerve cells in the posterior hypothalamic region, extending into the median eminence and almost entirely surrounding the base of the infundibulum.

2. one of the small irregular areas of gray substance on the ventromedial aspect of the pyramid of the medulla oblongata.

atomic nucleus  the central core of an atom, composed of protons and neutrons, constituting most of its mass but only a small part of its volume.

basal nucleus , nucleus basa´lis specific interconnected groups of masses of gray substance deep in the cerebral hemispheres and in the upper brain stem.

nucleus caeru´leus  a compact aggregation of pigmented neurons subjacent to the locus caeruleus, sometimes considered one of the medial reticular nuclei.

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 caudatus (caudate nucleus) in a lateral view of the left side of the brain.

central nuclei of thalamus  two small intralaminar nuclei, medial and lateral, situated in the internal medullary lamina.

centromedian nucleus of thalamus  the largest and most caudal of the intralaminar nuclei of the dorsal thalamus.

cochlear nuclei  the nuclei, anterior and posterior, of termination of sensory fibers of the cochlear part of the vestibulocochlear nerve, which partly encircle the inferior cerebellar peduncle at the junction of the medulla oblongata and pons.

cuneate nucleus , nucleus cunea´tus a nucleus in the medulla oblongata, in which the fibers of the fasciculus cuneatus synapse.

Deiters' nucleus  lateral vestibular nucleus; see nuclei vestibulares.

dentate nucleus , nucleus denta´tus the largest of the deep cerebellar nuclei lying in the white matter of the cerebellum.

droplet nuclei  see under infection.

emboliform nucleus , nucleus embolifor´mis a small cerebellar nucleus that lies between the dentate nucleus and globose nucleus and contributes to the superior cerebellar peduncles.

nucleus endopeduncula´ris  a small nucleus in the internal capsule of the hypothalamus, adjacent to the medial edge of the globus pallidus.

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

nucleus gra´cilis  a nucleus in the medulla oblongata, in which the fibers of the fasciculus gracilis of the spinal cord synapse.

hypoglossal nucleus , nucleus of hypoglossal nerve the nucleus of origin of the hypoglossal nerve in the medulla oblongata.

interpeduncular nucleus , nucleus interpeduncula´ris a nucleus between the cerebral peduncles immediately dorsal to the interpeduncular fossa.

lenticular nucleus , lentiform nucleus the part of the corpus striatum just lateral to the internal capsule, comprising the putamen and globus pallidus.

Meynert's nucleus  a group of neurons in the basal forebrain that has wide projections to the neocortex and is rich in acetylcholine and choline acetyltransferase; it undergoes degeneration in paralysis agitans and Alzheimer's disease.

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

oculomotor nucleus , nucleus oculomoto´rius the origin of the fibers of the oculomotor nerve, situated in the tegmentum of the mesencephalon immediately ventral to the central gray matter, between the medial longitudinal fasciculi. Innervation of the superior rectus of one eye originates in the contralateral oculomotor nerve nucleus; the other elements of the nucleus supply ipsilateral eye muscles via the oculomotor nerve.

olivary nucleus 

1. a folded band of gray substance enclosing a white core and producing the elevation (olive) of the medulla oblongata.

2. olive (2).

nucleus of origin  any of the groups of nerve cells in the central nervous system from which arise the motor, or efferent, fibers of the cranial nerves.

paraventricular nucleus of hypothalamus  a band of cells in the wall of the third ventricle in the anterior hypothalamic region; many of its cells are neurosecretory in function (secreting oxytocin) and project to the neurohypophysis.

pontine nuclei , nu´clei pon´tis groups of nerve cell bodies in the part of the pyramidal tract within the ventral part of the pons, upon which the fibers of the corticopontine tract synapse, and whose axons in turn cross to the opposite side and form the middle cerebellar peduncle.

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

raphe nuclei , nuclei of raphe a subgroup of the reticular nuclei of the brainstem, found in narrow longitudinal sheets along the raphae of the medulla oblongata, pons, and mesencephalon; they include many neurons that synthesize serotonin.

red nucleus  a distinctive oval nucleus (pink in fresh specimens) centrally placed in the upper mesencephalic reticular formation.

reticular nuclei  nuclei found in the reticular formation of the brainstem, occurring primarily in longitudinal columns in three groups: medial or intermediate reticular nuclei, lateral reticular nuclei, and reticular nuclei of the raphe.

nucleus ru´ber  red n.

salivary nuclei  two columns of cells in the posterolateral part of the reticular formation of the pons, together comprising the parasympathetic outflow for the supply of the salivary glands.

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

solitary nuclei  any of various nuclei of termination of the visceral afferent fibers of the facial, glossopharyngeal, and vagus nerves, which enter the solitary tract.

subthalamic nucleus , nucleus subthala´micus a nucleus on the medial side of the junction of the internal capsule and crus cerebri.

supraoptic nucleus  one just above the lateral part of the optic chiasm; many of its cells are neurosecretory in function (secreting antidiuretic hormone) and project to the neurohypophysis; other cells are osmoreceptors which respond to increased osmotic pressure to signal the release of antidiuretic hormone by the neurohypophysis.

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.

terminal nucleus  groups of nerve cells within the central nervous system on which the axons of primary afferent neurons of various cranial nerves synapse.

thoracic nucleus  see under column.

nuclei of trapezoid body  two groups of nerve cell bodies in or next to the trapezoid body.

trigeminal nuclei  four nuclei located along the trigeminal nerve, chiefly in the pons and medulla oblongata.

nu´clei vestibula´res  the four (superior, lateral, medial, and inferior) cellular masses in the floor of the fourth ventricle in which the branches of the vestibulocochlear nerve terminate.

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nucleus grac·i·lis (grs-ls)

n.

The medial of the three nuclei of the dorsal spinal column, receiving dorsal root fibers conveying sensory innervation of the leg.