(noo'klē-ŭs , noo'klē-ī‵)

Plural: nuclei

[L., nucleus, kernel]

1. A central point about which things are clustered.
2. The organelle in a eukaryotic cell that contains the chromosomes. SYN: cell nucleus.
3. In the central nervous system, a group of neuronal cell bodies that are clustered together and form a coherent demarcated mass in stained brain sections.
4. Atomic nucleus.

n. abducens A nucleus of the somatic motor column in the hindbrain. It lies in the floor of the fourth ventricle near the midline and is the origin of the abducens nerve (CN VI).

accessory oculomotor n.Edinger-Westphal nucleus.

accessory olivary n.Accessory olive.

n. accumbens A limbic nucleus that sits at the ventral head of the striatum, contiguous with the caudate and putamen and adjacent to the olfactory tubercle. The nucleus accumbens is part of the ventral striatum nuclei. Synapses in the nucleus accumbens use dopamine as their neurotransmitter. Increasing the activity of these synapses leads to a rewarding or pleasurable sensation. This is thought to explain in part the addictive effect of drugs such as cocaine and amphetamine, which increase the level of dopamine in the nucleus accumbens.

n. ambiguus A long, thin nucleus of the branchial motor column in the medulla. It is the origin of motor axons in both the glossopharyngeal and vagus nerves. Its axons innervate the muscles of swallowing and vocalization.

amygdaloid n.Amygdala (2).

angular n.Superior vestibular nucleus

anterior thalamic n.The most rostral of the thalamic nuclei. This nucleus is the only thalamic nucleus that is directly part of the limbic circuitry. It receives axons from the mammillary body via the mammillothalamic tract, from the hippocampus via the fornix, and from cholinergic nuclei in the basal forebrain. The nucleus sends axons to the medial cerebral cortices (cingulate gyrus, the anterior limbic area, and the parahippocampal gyrus).

SEE: limbic system for illus.

anterior olfactory n.The nucleus clustered along the olfactory tract. Some axons from the mitral cells in the olfactory bulb synapse on anterior olfactory neurons. The anterior olfactory neurons contribute axons to the olfactory tract. The anterior olfactory nucleus is distinct in most mammals but is sparse in primates.

arcuate n.A hypothalamic nucleus in the ventral wall of the third ventricle near the pituitary stalk. The arcuate nucleus produces inhibiting and releasing factors (adrenocorticotropic hormone, beta-lipotropic hormone, and beta-endorphin) for pituitary hormones. SYN: infundibular nucleus.

atomic n.In chemistry, the heavy positively charged central part of an atom, containing protons, neutrons, and most of the atomic mass. SYN: nucleus (4).

auditory n.The nucleus where the auditory nerves arise.

basal n.

SEE: under Meynert, Theodor H..

n. basalis

SEE: under Meynert, Theodor H..

n. basalis of Meynert

SEE: under Meynert, Theodor H..

bed n. of the stria terminalis Any of the numerous nuclei on which some axons of the stria terminalis synapse. These nuclei lie lateral to the columns of the fornix and dorsal to the anterior commissure.

n. of Burdach

SEE: under Burdach, Karl.

caudal pontine reticular nNucleus reticularis pontis caudalis

caudate n.One of the basal nuclei. The caudate lies deep in the cerebral hemisphere; its head lies near the base of the anterior horn of the lateral ventricle, and its tail follows the ventricle as it arches over the thalamus and downward. The tip of the tail of the caudate ends alongside the caudal end of the amygdala, and many axons that originate in the amygdala synapse in the caudate and other parts of the striatum. The caudate nucleus and the putamen form the striatum. SYN: nucleus caudatus; intraventricular nucleus.

n. caudatus Caudate nucleus.

cell n.Nucleus (2).

central cervical n.A nucleus of secondary sensory neurons near the midline of the posterior horn of spinal segments C1-C4. Inputs to this nucleus include direct spinal ganglion axons; outputs from this nucleus cross the midline and run to the cerebellum.

central n. of the thalamus A group of nuclei in the middle part of the thalamus. SYN: centromedian nucleus.

centromedian n.Central nucleus of the thalamus.

cerebellar n.Any of four deep, i.e., below the cerebellar cortex, nuclei of each half of the cerebellum (from lateral to medial): the dentate, the emboliform, the globose, and the fastigial nuclei.

cervical n.

SEE: central cervical nucleus.

cochlear n.

SEE: dorsal cochlear nucleus; ventral cochlear nucleus.

cranial nerve n.Any of the nuclei of the 12 pairs of nerves that carry signals directly to or from the brain.

cuneate n.A secondary sensory nucleus lateral to the gracile nucleus in the caudal hindbrain near the junction with the spinal cord. Axons of the fasciculus cuneatus in the dorsal columns synapse in this nucleus. Neurons in the nucleus send their axons in the contralateral medial lemniscus to synapse in the ventral posterior lateral nucleus of the thalamus. The secondary afferent neurons of the cuneate nucleus mediate fine touch, conscious proprioception, and vibratory sense from the upper limbs.

cuneiform n.A nucleus in the midbrain reticular formation lying directly under the superior and inferior colliculi. Axons from the cuneiform nucleus project widely, caudally as far as the hindbrain and rostrally as far as the diencephalon. SYN: reticular formation..

n. of Darkschewitsch

SEE: Nucleus of Darkschewitsch..

dentate n.The largest and most lateral of the four pairs of deep cerebellar nuclei. In cross-sections the dentate nucleus has a serpentine shape. It receives axons from the cerebellar cortex and from the brainstem and sends axons to the red nucleus and the thalamus via the superior cerebellar peduncle.

n. of the diagonal band A nucleus of large cholinergic neurons mingled with the diagonal band . This nucleus has reciprocal connections with the hippocampus. Like the large cholinergic neurons in the nucleus basalis, the neurons in the nucleus of the diagonal band degenerate if the brain develops Alzheimer disease.

diploid n.A cell nucleus that contains double the normal number of chromosomes.

dorsal cochlear n.A nucleus of the special sensory column in the hindbrain, forming the acoustic tubercle. Axons of the primary sensory cells in the spiral ganglion run in the vestibulocochlear nerve (CN VIII) and synapse in the dorsal and ventral cochlear nuclei. About half of the axons from neurons in the cochlear nuclei cross the midline in the trapezoid body and then join the uncrossed axons from the contralateral cochlear nuclei. Together, these axons ascend the lateral lemniscus to synapse in the inferior colliculus in the midbrain.

dorsal n. of the lateral lemniscus One of the two distinguishable nuclei clustered in the upper (rostral) end of the lateral lemniscus near the inferior colliculi. These nuclei are part of the auditory circuitry.

dorsal motor n. of the vagus A nucleus of the visceral motor column in the hindbrain. This nucleus lies in the floor of the fourth ventricle lateral to the hypoglossal nucleus and is the origin of preganglionic parasympathetic axons by which the vagus nerve (CN X) modulates secretory activity in the gastrointestinal system. SYN: dorsal nucleus of the vagus; nucleus of the vagus.

dorsal n. of the spinal cord Clarke column.

n. dorsalis Clarke column

SEE: under Clarke, Jacob A. L..

dorsal raphe n.A midbrain nucleus that lies in the midline in the tegmentum, below the periaqueductal gray matter. It sends serotonergic axons to the striatum via the medial forebrain bundle and receives axons from the interpeduncular nucleus. SYN: raphe nucleus.

dorsal n. of the vagus Dorsal motor nucleus of the vagus.

dorsal n. of the spinal cord A nucleus of gray matter lying at the base of the dorsal horn of the gray matter and extending from the seventh cervical to the third lumbar segments. These cells give rise to fibers of the dorsal spinocerebellar tract. SYN: Clarke column.

ectoblastic n.A nucleus in the cells of the epiblast.

Edinger-Westphal n.

SEE: Edinger-Westphal nucleus.

emboliform n.A deep nucleus of the cerebellum, forming the interposed nuclear group together with the globose nucleus.

external cuneate n.A secondary sensory nucleus in the caudal hindbrain lying along the lateral edge of the cuneate nucleus. It receives proprioceptive information from the upper half of the body, is the source of the cuneocerebellar tract, and is the upper limb homologue of the Clarke column. SYN: lateral cuneate nucleus.

SEE: Clarke column under Clarke, Jacob A. L..

facial motor n.A nucleus of the branchial motor column in the pontine region of the hindbrain. This nucleus is a column of cholinergic neurons in the ventrolateral tegmentum. It is the origin of motor axons in the facial nerve (CN VII), which innervate the muscles of facial expression.

fastigial n.The most medial of the four pairs of deep cerebellar nuclei. The fastigial nucleus receives inputs from the vestibular nuclei and from the medial cerebellar cortex.

fertilization n.A nucleus produced by the joining of the male and female nuclei in the fertilization of the ovum.

free n.A cell nucleus that is no longer surrounded by the other intracellular components.

n. funiculi gracilis An elongated nucleus of gray matter in the dorsal pyramid of the medulla oblongata of the brain. SYN: postpyramidal nucleus.

germinal n.A cell nucleus resulting from the union of male and female pronuclei.

gigantocellular reticular n.Nucleus reticularis gigantocellularis.

globose n.A deep nucleus of the cerebellum. It and the emboliform nucleus form the interposed nucleus, which lies between the dentate and fastigial nuclei. SYN: posterior interposed nucleus.

gonad n.Micronucleus (2).

gracile n.A secondary sensory nucleus medial to the cuneate nucleus in the caudal hindbrain near the junction with the spinal cord. Axons of the fasciculus gracilis in dorsal columns synapse in this nucleus, and neurons in the nucleus send their axons in the contralateral medial lemniscus to synapse in the ventral posterior lateral nucleus of the thalamus. The gracile nucleus is a way station for discriminative somatic sensory information from the leg and trunk. SYN: nucleus gracilis.

n. gracilis Gracile nucleus.

gustatory n.A nucleus of the visceral sensory column in the hindbrain. The gustatory nucleus comprises the rostral third of the nucleus of the solitary tract. It receives axons carrying sensory information from the taste buds via three cranial nerves, the facial (CN VII), the glossopharyngeal (CN IX), and the vagus (CN X). Axons from the gustatory nucleus synapse in the semilunar nucleus, a component of the ventromedial subdivision of the ventral posterior nucleus of the thalamus.

habenular n.A small set of nuclei in the limbic system found just rostral to the pineal gland in the roof of the third ventricle. The habenula receives axons from the limbic forebrain via a compact tract, the stria medullaris. In turn, the habenula sends a compact bundle of axons, the fasciculus retroflexus (habenulo-interpeduncular tract), to innervate the interpeduncular nuclei of the midbrain.

SEE: limbic system for illus.

haploid n.A cell nucleus with half the normal number of chromosomes, as in germ cells (ova and sperm) following the normal reduction divisions in gametogenesis.

hypoglossal n.A nucleus of the somatic motor column, found near the midline in the caudal hindbrain. It innervates all the muscles in the tongue and is the origin of the hypoglossal nerve (CN XII).

hypothalamic n.A set of nuclei in the ventral diencephalon on either side of the lower recess of the third ventricle. These nuclei 1) regulate the preganglionic motor neurons of the sympathetic and parasympathetic nervous systems; 2) control the secretions of the anterior lobe of the pituitary gland ; 3) secrete hormones (such as oxytocin and vasopressin) through the posterior lobe of the pituitary gland ; and 4) modulate the limbic system, as by the mammillary bodies.

SEE: limbic system for illus.

n. of the inferior colliculus A three-part nucleus forming the caudal pair of bulges (the inferior colliculi) in the tectum of the midbrain. This nucleus is an auditory relay center: the cochlear and other hindbrain auditory nuclei send information rostrally in the lateral lemniscus, axons of the lateral lemniscus synapse in the inferior colliculus, and axons originating in the inferior colliculus take the brachium of the inferior colliculus rostrally to synapse in the medial geniculate body of the thalamus.

inferior olivary n.Inferior olive.

inferior salivatory n.A nucleus of the visceral motor column in the pontine hindbrain just rostral to the medulla. This nucleus is the origin of the preganglionic parasympathetic axons of the glossopharyngeal nerve (CN IX) that synapse in the otic ganglion and regulate secretions of the parotid gland .

inferior vestibular n.One of the four vestibular nuclei in the special sensory column in the hindbrain. It is lateral to the medial vestibular nucleus and lies in the floor of the fourth ventricle near the lateral edge. It receives axons from the vestibular ganglia via the vestibulocochlear nerve (CN VIII) and from the deep cerebellar nuclei and sends axons to the cerebellum.

infundibular n.Arcuate nucleus.

n. intercalatus A reticular nucleus inside the floor of the fourth ventricle, between the hypoglossal nucleus and the dorsal motor nucleus of the vagus.

interpeduncular n.A ventral nucleus of the midbrain tegmentum lying between the left and right substantia nigrae, which cap the two cerebral peduncles. It receives axons from the habenula via the habenulo-interpeduncular tract and sends axons dorsally to the midbrain raphe nuclei.

SEE: limbic system for illus.

interphase n.The nucleus of a cell in interphase in which the nuclear membrane is visible and undisrupted and the chromatin is not condensed.

interstitial n. of Cajal A midbrain nucleus found both interspersed among and lateral to the medial longitudinal fasciculus, just rostral to the oculomotor nucleus. The interstitial nucleus of Cajal is one of the accessory oculomotor nuclei.

intraventricular n.Caudate nucleus.

lateral cuneate n.External cuneate nucleus.

lateral geniculate n.The visual relay nucleus of the thalamus. It comprises nuclei located on the posterior aspect of the thalamus, lateral to the medial geniculate nucleus. Axons from the retinal ganglion cells of the retina reach the lateral geniculate via the optic nerve and optic tract and then synapse in topographic order. The outflow axons from the lateral geniculate neurons run in the optic radiation and synapse in the primary visual cortex in the occipital hemisphere, again maintaining their topographic organization.

n. of the lateral lemniscus

SEE: lateral lemniscus..

lateral posterior n. of the thalamus A nucleus that lies dorsal to the ventral posterior nucleus.

SEE: thalamic nucleus.

lateral reticular n.A reticular nucleus found in the caudal hindbrain. This nucleus receives axons from the spinal cord via the spinoreticular tract and from the red nucleus and sends axons to the cerebellum.SYN: nucleus reticularis lateralis.

lateral septal n.A member of the ventral group of nuclei in the septal region of each cerebral hemisphere. The lateral septal nucleus is a part of the limbic system; receives axons from the hippocampus, the hypothalamus, and monoaminergic axons from the brainstem; and sends axons to the hypothalamus, habenula, thalamus, and midbrain.

SEE: limbic system for illus.

lateral vestibular n.One of the four vestibular nuclei in the special sensory column in the hindbrain. The lateral vestibular nucleus extends rostrally, beginning near the front end of the inferior vestibular nucleus. It lies in the floor of the fourth ventricle near the lateral edge; it receives axons from the vestibular ganglia (via the vestibulocochlear nerve [CN VII]) and from the deep cerebellar nuclei, and it sends axons to the cerebellum and to all levels of the ipsilateral spinal cord via the vestibulospinal tract. SYN: Deiter nucleus.

lentiform n.The putamen and the globus pallidus considered together.

n. lentis The core or inner dense section of the crystalline lens.

mammillary n.Any of three nuclei (lateral mammillary nucleus, intermediate mammillary nucleus, medial mammillary nucleus.

SEE: limbic system for illus.

masticatory n.Trigeminal motor nucleus

medial geniculate n.The auditory relay nucleus of the thalamus. It is on the posterior aspect of the thalamus above the cerebral peduncle, receives input from the inferior colliculus, and sends axons to the primary auditory cortex (superior temporal gyrus of Heschl [area 41]), in which the neurons are organized according to pitch.

medial mammillary nThe largest of the three mammillary nuclei (medial, intermediate, and lateral mammillary nuclei). The medial mammillary nucleus is spherical and nearly fills the mammillary body. The mammillary nuclei are functionally associated with the limbic system, receive axons from the hippocampus (via the fornix) and the midbrain tementum (via the mammillary peduncle), and send axons to the anterior nucleus of the thalamus (via the mammillothalamic tract) and the midbrain tegmentum (via the mammillotegmental tract).

SEE: limbic system for illus.

medial septal n.A nucleus alongside the diagonal band in the septal region of each cerebral hemisphere. This nucleus sends axons to and receives axons from the hippocampus.

medial vestibular n.One of the four vestibular nuclei in the special sensory column in the hindbrain. The medial vestibular nucleus is medial to the inferior vestibular nucleus. It lies in the floor of the fourth ventricle near the lateral edge, it receives axons from the vestibular ganglia via the vestibulocochlear nerve (CN VIII) and from the deep cerebellar nuclei, and it sends axons to the cerebellum and to the spinal cord via the medial longitudinal fasciculus.

median raphe n.A midline reticular nucleus in the caudal midbrain or rostral pontine tegmentum. This nucleus receives axons from the interpeduncular nucleus, and it sends serotonergic axons to the forebrain limbic areas and to the cerebral cortex via the medial forebrain bundle. SYN: superior central nucleus.

mesencephalic trigeminal n.A nucleus of the general somatic sensory column in the midbrain and rostral hindbrain. It lies in the lateral edge of the gray matter, extending from the cerebral aqueduct to the rostral fourth ventricle. The large unipolar neurons of this nucleus are like dorsal root ganglion neurons, and the mesencephalic trigeminal nucleus contains the only primary sensory neurons found inside the central nervous system. The afferent fibers of this nucleus follow the motor root of the trigeminal nerve (CN V3) to the mouth from which they carry pressure, proprioceptive, stretch, and kinesthetic information; the efferent fibers synapse in the trigeminal motor nucleus. SYN: trigeminal mesencephalic nucleus.

n. of Meynert

SEE: under Meynert, Theodor H..

mother n.A cell nucleus that divides into two or more parts to form daughter nuclei.

motor n.A nucleus participating in the formation or the execution of the output programs of the central nervous system.

motor n. of the trigeminal nerve Trigeminal motor nucleus

noradrenergic n.A nucleus with neurons that use norepinehrine as their neurotransmitter, e.g., the locus coeruleus.

oculomotor n.A nucleus in the gray matter below the cerebral aqueduct in the midbrain at the rostral end of the somatic motor column. It communicates via the oculomotor nerve (CN III) with axons that innervate four extraocular eye muscles: the medial, the inferior, the superior recti, and the inferior oblique.

olivary n.

SEE: under inferior olive; superior olive.

n. of origin The nucleus containing the neuronal cell body of an axon in the central nervous system.

parabigeminal n.Any of the scattered nuclei in the lateral-most edge of the midbrain below (ventral to) the inferior colliculus. The parabigeminal nuclei are satellites of the superior colliculi; they receive axons from and send axons to the ipsilateral and contralateral superior colliculi.

paramedian reticular n.One of the three major groups of reticular nuclei in the caudal hindbrain.

paraventricular n.A large-celled nucleus beneath the ependymal layer lining the third ventricle in the supraoptic region of the hypothalamus. Axons of the paraventricular nucleus and axons from the neighboring supraoptic nucleus form the supraopticohypophyseal tract. The axons of this tract regulate water balance in the body and secrete vasopressin from their terminals in the posterior lobe of the pituitary gland . Its cells also seem to stimulate the sensation of thirst. The supraoptic and paraventricular nuclei also produce oxytocin.

SEE: hypothalamic nucleus.

phrenic n.A column of motor neurons in the center of the ventral horn of spinal cord segments C3-C7. Axons from this nucleus innervate the muscles of the diaphragm.

pontine n.Any of the neurons interspersed with the corticospinal axons in the ventral pontine hindbrain. The inputs to the pontine nuclei are mainly axons from sensory and motor areas of the cerebral cortex. The outputs are axons that cross the midline and ascend into the cerebellum via the middle cerebellar peduncle (brachium pontis).

pontine reticular n.Nucleus reticularis pontis.

n. of the posterior commissure Any of the small midbrain nuclei interspersed in the axons of the posterior commissure just rostral to the oculomotor nucleus. The nuclei of the posterior commissure are members of the accessory oculomotor (preoculomotor) nuclei, which are composed of interneurons concerned with eye movements and reflex gaze coordination and which receive axons from the medial longitudinal fasciculus.

posterior interposed n.Globose nucleus .

posterior thoracic n.Clarke column.

postpyramidal n.Nucleus funiculi gracilis.

preoptic n.Either of a pair of hypothalamic nuclei (medial and lateral) in the most anterior sector, the preoptic region, of the wall of the third ventricle. Various parts of these nuclei appear to inhibit arousal during sleep, influence temperature regulation, influence the perception of thirst, regulate the release of gonadotropins from the anterior pituitary (adenohypophysis), and influence sexual behaviors.

n. prepositus A motor processing nucleus in the midline gray matter of the rostral hindbrain. It contains interneurons that coordinate signals destined for the oculomotor, trochlear, and abducens nuclei, the motor nuclei of the extraocular eye muscles.

pretectal n.One of the motor processing nuclei in the midbrain immediately rostral to the superior colliculus. The nuclei in this region coordinate the output signals for the pupillary light reflex.

principal sensory trigeminal n.The most rostral nucleus of the sensory column. The principal sensory trigeminal nucleus receives axons from the trigeminal nerve (CN V) carrying fine touch, two-point discrimination, and pressure signals from the face and mouth. The principal sensory trigeminal nucleus sends axons that cross the midline to the ventral posterior medial nucleus of the thalamus via the anterior trigeminothalamic tract. In addition, the principal sensory trigeminal nucleus sends axons to the ipsilateral ventral posterior medial nucleus in a separate tract called the posterior trigeminothalamic tract that convey sensation from the oral cavity. Therefore the oral cavity has bilateral representation in the thalamus.

n. proprius The nucleus comprising the middle third of the dorsal horn of the spinal cord. Neurons in this layer receive spinal (dorsal root) ganglion cell axons carrying pain and temperature information. Many of these neurons send their axons across the midline to join the contralateral spinothalamic tract.

n. pulposus The center cushioning gelatinous mass lying within an intervertebral disk. It is the remnant of the notochord.

pyramidal n.A nucleus of gray matter near the olivary nucleus in the medulla that sends fibers to the cerebellum.

raphen.Any of a set of midline reticular nuclei in the midbrain and hindbrain tegmentum that send serotonergic axons widely throughout the forebrain brain via the medial forebrain bundle. Raphe nuclei appear to regulate sleep and aggressive behavior and to influence pain perception.

n. raphe magnus A raphe nucleus in the rostral medulla.

red n.A reddish spherical nucleus in the midbrain tegmentum. This nucleus is a part of the motor system. It receives axons from the deep cerebellar nuclei via the superior cerebellar peduncle (brachium conjunctivum) and from the motor areas of the cerebral cortex,and sends axons to the contralateral spinal cord via the rubrospinal tract. SYN: nucleus ruber.

reproductive n.Micronucleus (2).

reticular n.A group of related neurons in the spinal cord, brainstem, and thalamus.

n. reticularis gigantocellularis A segment of the reticular formation that is found at the level of the inferior olive in the hindbrain and contains large neurons. Its descending axons contribute to the reticulospinal tract; activation of this nucleus inhibits motor neuron activity in the spinal cord, e.g., during sleep.SYN: nucleus reticularis magnocellularis.

n. reticularis lateralis Lateral reticular nucleus.

n. reticularis magnocellularis Nucleus reticularis gigantocellularis.

n. reticularis pontis Any of the reticular nuclei in the rostral hindbrain, e.g., the nucleus reticularis pontis caudalis.

n. reticularis pontis caudalis A rostral extension of the nucleus reticularis gigantocellularis of the hindbrain. The nucleus reticularis pontis caudalis sends reticulospinal axons caudally into the spinal cord via the medial longitudinal fasciculus and sends ascending axons as far rostrally as the thalamus via the central tegmental tract. SYN: caudal pontine reticular nucleus.

b reticularis ventralis A reticular nucleus found in the caudal hindbrain.

reticulotegmental nA reticular nucleus found at the pontine level of the hindbrain. It receives axons from the cerebral cortex and the cerebellum, and it sends axons to the cerebellum.

roof nA small nucleus of gray matter in the white matter of the vermis of the cerebellum.

n. ruber Red nucleus.

salivatory n.A two-part visceral motor nucleus comprising the superior and the inferior salivatory nuclei.

segmentation n.The cell nucleus of a zygote formed by fusion of the male and female pronuclei.

sensory n.A nucleus participating in the reception or the interpretation of input to the central nervous system.

sensory n. of the trigeminal nerve

SEE: mesencephalic trigeminal nucleus; principal sensory trigeminal nucleus; spinal trigeminal nucleus.

septal n.The dorsal, ventral, medial, or caudal septal nucleus. The septal area is the subcallosal area plus the paraterminal gyrus, i.e., the anterior and medial region of the cerebral hemispheres above the lamina terminalis and below (and including) the septum pellucidum. The septal nuclei receive inputs from the hippocampus and the hypothalamus; the septal nuclei project to the hypothalamus, the habenula, the thalamus, and , via the medial forebrain bundle, to the midbrain tegmentum.

SEE: limbic system for illus.

sexually dimorphic nA central nervous system nucleus that has different characteristics, such as size or number of cells, in males and in females,e.g., in the preoptic region of the hypothalamus.

solitary n.Nucleus of the solitary tract.

n. of the solitary tract The only brainstem nucleus of the visceral sensory column. It runs the length of the caudal hindbrain in the lateral subventricular gray matter alongside the solitary tract. At the caudal end of the hindbrain, the right and left nuclei of the solitary tract merge in the midlineand form the commissural nucleus. The facial nerve (CN VII), the glossopharyngeal nerve (CN IX), and the vagus nerve (CN X) provide the main inputs to the nucleus, bringing information about taste, blood pressure, and blood chemistry. The nucleus then sends information throughout the hindbrain to reflex centers controlling cardiovascular, respiratory, and gastrointestinal homeostasis.The nucleus is also an important source of input to the hypothalamus.SYN: solitary nucleus.

sperm n.The head of the spermatozoon.

spinal accessory nA branchial motor column nucleus that extends caudally from the end of the nucleus ambiguus into the ventral horn of spinal cord segments C1-C4. Axons of the neurons in the spinal accessory nucleus leave C1-C4 spinal cord levels laterally via rootlets and collect into a thin nerve that runs up along the side of the spinal cord and into the skull through the foramen magnum. The nerve then exits the cranial vault through the jugular foramen to innervate the trapezius and sternocleidomastoid.

spinal trigeminal nA nucleus of the general somatic sensory column that extends through the entire hindbrain as a continuation of the posterior horn of the spinal cord and merges rostrally into the principal sensory trigeminal nucleus. The spinal trigeminal nucleus receives axons from the trigeminal nerve (CN V) and other cranial nerves and carries pain and temperature signals from the face and mouth. This nucleus sends axons to the ventral posterior nucleus of the thalamus via the medial lemniscus and the spinothalamic tract. SYN: trigeminal spinal nucleus.

subcoeruleus n.A reticular nucleus in the pontine hindbrain. It is involved in memory consolidation and rapid eye movement sleep.

subthalamic n.A basal ganglia nucleus that is found under the thalamus in the base of the diencephalon and lies between the thalamus and the cerebral peduncle. The subthalamic nucleus is a satellite of the globus pallidus with which it has reciprocal connections. Lesions of the subthalamic nucleus on one side of the brain produce hemiballismus. SYN: corpus Luysii; corpus subthalamicum; Luys body.

subthalamic reticular n

SEE: field of Forel.

superior central nMedian raphe nucleus

superior olivary n.Superior olive.

superior salivatory n.A nucleus of the visceral motor column in the pontine hindbrain just rostral to the medulla. This nucleus is the origin of those preganglionic parasympathetic axons of the intermediate nerve that synapse in the pterygopalatine ganglion to regulate secretions of the lacrimal and mucosal gland s of the nose and mouth and inthe submand ibular ganglion to regulate secretions of the sublingual and submand ibular salivary gland s.

superior vestibular n.The smallest and most rostral of the four vestibular nuclei, which lie in the special sensory column in the hindbrain. The superior vestibular nucleus lies in the floor of the fourth ventricle near the lateral edge; it receives axons from the vestibular ganglia (via the vestibulocochlear nerve [CN VIII]) and from the deep cerebellar nuclei and sends axons to the cerebellum. SYN: angular nucleus; Bechterew nucleus.

SEE: vestibular nucleus.

suprachiasmatic n.A small hypothalamic nucleus lying at the base of the third ventricle, directly above the optic chiasm. This nucleus generates the brain's circadian rhythm. To entrain its rhythm with the natural day-night cycle, the nucleus is innervated by optic axons via the accessory optic tract; it also receives axons from the lateral geniculate nucleus of the thalamus, and serotonergic axons from the midbrain raphe nuclei. The suprachiasmatic nucleus sends most of its axons to the paraventricular nucleus of the hypothalamus.

supraoptic n.A large-celled nucleus of the hypothalamus lying above the rostral ends of the optic tracts and lateral to the optic chiasm.

SEE: paraventricular nucleus.

target n.In the central nervous system, the nucleus that contains the neuronal cell body (or its dendrites) on which that axon synapses.

tegmental n.One of several masses of gray matter lying in the tegmentum of the midbrain and upper portion of the pons. It includes the dorsal, pedunculopontile, reticular, and ventral nuclei.

n. of termination Any of the nuclei the brain and medulla in which fibers of a nerve or nerve tract terminate.

thalamic n.Any of the more than 27 nuclei of the thalamus. The thalamic nuclei are named according to their position in the thalamus. The medial nuclei and dorsal nuclei are separated from the lateral nuclei and ventral nuclei by the internal medullary lamina. The thalamic nuclei filter and modify the signals that the nervous system sends to the cerebral cortices. Thalamic nuclei are divided into five groups by their patterns of connectivity: 1) the nuclei in the base of the thalamus (ventroposterior nuclei, lateral geniculate nuclei, medial geniculate nuclei) receive all the sensory information from the body (smell) and send information to the primary sensory areas of the cerebral cortices; 2) the ventral anterior nuclei and ventral lateral nuclei (the VA-VL complex) receive motor programs from the globus pallidus and the cerebellum and send information to the motor areas of the cerebral cortices; 3) The dorsomedial nucleus, the lateral posterior nuclei and lateral dorsal nuclei, and the pulvinar nucleus receive information from the association areas of the cerebral cortices and from noncortical regions of the brain and send information back to the association cortices; 4) the anterior nucleus receives information from the mammillary body and from the fornix and sends information to the cingulate gyrus of the cerebral cortex; 5) the small nuclei in the internal medullary lamina (intralaminar nuclei) and the nuclei along the midline of the thalamus receive information from the cerebral cortices, the cerebellum, the reticular formation and send information throughout the cerebral cortices.

thoracic n.A column of large neurons in the posterior gray column of the spinal cord. These cells give rise to the dorsal spinocerebellar tract on the same side.

n. of the tractus solitarius

SEE: tractus solitarius.

n. of the trapezoid body A nucleus in the trapezoid body in the hindbrain, some of whose axons cross the midline through the trapezoid body.

trigeminal mesencephalic nMesencephalic trigeminal nucleus.

trigeminal motor nA somatic motor nucleus in the rostral hindbrain. It is found in the ventral pontine tegmentum between the spinal trigeminal nucleus and the superior olive. It is the origin of motor axons in the mand ibular division of the trigeminal nerve (CN V3). Its axons innervate the muscles of mastication, as well as the tensor tympani, tensor palati, the anterior belly of the digastric and the mylohyoid.SYN: masticatory nucleus; motor nucleus.

trigeminal sensory n.

SEE: mesencephalic trigeminal nucleus; principal sensory trigeminal nucleus; spinal trigeminal nucleus.

trigeminal spinal n.Spinal trigeminal nucleus.

trochlear n.A small nucleus of the somatic motor column in the hindbrain. It is rostral to the medial longitudinal fasciculus, just caudal to the oculomotor nucleus, and it is the origin of the axons of the trochlear nerve (CN IV).

tuberal n.Any of the nuclei (lateral tuberal nucleus, medial tuberal nucleus, anteriortuberal nucleus, posterior tuberal nucleus) in the hypothalamus.

tuberomammillary nA hypothalamic nucleus found just lateral to the medial mammillary nucleus. It is characterized by histaminergic axons that widely and diffusely innervate the entire brain. Neurons of this nucleus fire regularly when a person is awake and rarely during sleep. Stimulation of the tuberomammillary nucleus raises blood pressure and heart rate.

n. of the vagus

SEE: dorsal motor nucleus of the vagus.

ventral cochlear n.A nucleus of the special sensory column in the hindbrain. It forms a bulge around the entering cochlear nerve. Axons of the primary sensory cells in the spiral ganglion run in the vestibulocochlear nerve (CN VIII) and synapse in the dorsal and ventral cochlear nuclei. About half of the axons from neurons in the cochlear nuclei cross the midline in a tract called the trapezoid body and join the uncrossed axons from the contralateral cochlear nuclei. Together, these axons ascend in a tract called the lateral lemniscus to synapse in the inferior colliculus in the midbrain.

ventral n. of the lateral lemniscus One of the two distinguishable nuclei clustered in the upper (rostral) end of the lateral lemniscus near the inferior colliculi. These nuclei are part of the auditory circuitry.

ventral posterior lateral n of the thalamus One of the two major divisions of the ventral posterior nucleus, the somatic sensory relay nucleus of the thalamus. The ventral posterior lateral nucleus is the target of the medial lemniscus (touch and position sense from the body) and of many spinothalamic tract axons, and it sends axons to the sensory areas of the cerebral cortices.

ventral posterior medial of the thalamus

ABBR: VPM