| inferior olivary nucleus | A large aggregate of small densely packed nerve cells arranged in folded laminae shaped like a purse with the opening (hilum) directed medially. It corresponds in position to the oliva, projects to all parts of the contralateral half of the cerebellar cortex by way of the olivocerebellar tract, and is the only source of cerebellar climbing fibres. Its afferent connections include fibres from the spinal cord, the dentate nucleus and motor cortex, but its major input appears to be the central tegmental tract originating from multiple nuclei at midbrain levels. Synonym: nucleus olivaris. (05 Mar 2000) |
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| inferior salivary nucleus | A group of preganglionic parasympathetic motor neurons located in the reticular formation of the medulla oblongata dorsal to the nucleus ambiguus; its axons leave the brain with the glossopharyngeal nerve and govern secretion from the parotid gland by the intermediary of the ganglion oticum; cells of the inferior and superior nucleus are scattered and overlapping in lateral regions of the reticular formation. Synonym: nucleus salivatorius inferior, inferior salivary nucleus. (05 Mar 2000) |
| inferior salivatory nucleus | A group of preganglionic parasympathetic motor neurons located in the reticular formation of the medulla oblongata dorsal to the nucleus ambiguus; its axons leave the brain with the glossopharyngeal nerve and govern secretion from the parotid gland by the intermediary of the ganglion oticum; cells of the inferior and superior nucleus are scattered and overlapping in lateral regions of the reticular formation. Synonym: nucleus salivatorius inferior, inferior salivary nucleus. (05 Mar 2000) |
| inferior vestibular nucleus | Nucleus vestibularis inferior. See: vestibular nucleus. (05 Mar 2000) |
| intercalated nucleus | A small collection of nerve cells in the medulla oblongata lying lateral to the hypoglossal nucleus. Synonym: nucleus intercalatus, Staderini's nucleus. (05 Mar 2000) |
| intermediolateral nucleus | The cell column that forms the lateral horn of the spinal cord's gray matter. Extending from the first thoracic through the second lumbar segment, the column contains the autonomic motor neurons that give rise to the preganglionic fibres of the sympathetic system. Synonym: intermediolateral cell column of spinal cord, nucleus intermediolateralis. (05 Mar 2000) |
| intermediomedial nucleus | A small group of scattered visceral motor neurons immediately ventral to the thoracic nucleus in the thoracic and upper two lumbar segments of the spinal cord; considered to receive visceral afferent fibres at all spinal levels. Synonym: nucleus intermediomedialis. (05 Mar 2000) |
| interpeduncular nucleus | A median, unpaired, ovoid cell group at the base of the midbrain tegmentum between the cerebral peduncles; it receives the retroflex fasciculus from the habenula, and projects to the raphe region (raphe nuclei) and periaqueductal gray substance of the midbrain. Synonym: nucleus interpeduncularis, ganglion isthmi, Gudden's ganglion, intercrural ganglion, interpeduncular ganglion. (05 Mar 2000) |
| interpositus nucleus | Collective term denoting the combined globosus nuclei and emboliform nuclei of the cerebellum; more correctly used as interposed nuclei as it identifies two cell groups. Synonym: nucleus interpositus. (05 Mar 2000) |
| interstitial nucleus | A group of widely spaced, medium-sized neurons in the dorsomedial region of the upper mesencephalic tegmentum, immediately lateral to the nucleus of Darkschewitsch; together with the latter, the interstitial nucleus is closely associated with the medial longitudinal fasciculus, via which it receives fibres from the vestibular nuclei and projects crossed fibres via the posterior commissure to the oculomotor nucleus; also projects fibres to all spinal levels. It is believed to be involved in the integration of head and eye movements, particularly eye movements of a vertical or oblique nature. Synonym: nucleus interstitialis, interstitial nucleus of Cajal. (05 Mar 2000) |
| interstitial nucleus of Cajal | A group of widely spaced, medium-sized neurons in the dorsomedial region of the upper mesencephalic tegmentum, immediately lateral to the nucleus of Darkschewitsch; together with the latter, the interstitial nucleus is closely associated with the medial longitudinal fasciculus, via which it receives fibres from the vestibular nuclei and projects crossed fibres via the posterior commissure to the oculomotor nucleus; also projects fibres to all spinal levels. It is believed to be involved in the integration of head and eye movements, particularly eye movements of a vertical or oblique nature. Synonym: nucleus interstitialis, interstitial nucleus of Cajal. (05 Mar 2000) |
| oculomotor nucleus | The composite group of motor neurons innervating all of the external eye muscles except the musculus rectus lateralis and musculus obliquus superior, and including the musculus levator palpebrae superioris; the most rostral component of the nucleus is the Edinger-Westphal nucleus which innervates the musculi sphincter pupillae and ciliaris via the ciliary ganglion. The oculomotor nucleus lies in the rostral half of the midbrain, near the midline in the most ventral part of the central gray substance; fibres of the medial longitudinal fasciculus form its lateral borders. Synonym: nucleus nervi oculomotorii, nucleus of oculomotor nerve. (05 Mar 2000) |
| Onuf's nucleus | Small somatic motor neurons in the ventral horn of the spinal cord at sacral 2 level which innervate the vesicorectal sphincters, that is, the external anal and the urethral sphincter; O.'s nucleus has been identified in the cat, dog, and humans. (05 Mar 2000) |
| tail of caudate nucleus | The elongated posterior extension of the caudate nucleus that parallels the body and inferior horn of the lateral ventricle. Synonym: cauda nuclei caudati, cauda striati. (05 Mar 2000) |
| tectal nucleus | The most medial of the cerebellar nuclei, lying medial to the interpositus nucleus, near the midline, in the white matter underneath the vermis of the cerebellar cortex. It receives the axons of Purkinje cells from all parts of the vermis. Its major projection is to the vestibular nuclei and medullary reticular formation. Synonym: nucleus fastigii, fastigatum, nucleus tecti, roof nucleus, tectal nucleus. (05 Mar 2000) |