| medial forebrain bundle | A complex group of fibres arising from the basal olfactory regions, the periamygdaloid region, and the septal nuclei, and passing to the lateral hypothalamus. Some fibres continue into the tegmentum. (12 Dec 1998) |
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| medial longitudinal bundle | A longitudinal bundle of fibres extending from the upper border of the mesencephalon into the cervical segments of the spinal cord, located close to the midline and ventral to the central gray matter; it is composed largely of fibres from the vestibular nuclei ascending to the motor neurons innervating the external eye muscles (abducens, trochlear, and oculomotor nuclei), and descending to spinal cord segments innervating the musculature of the neck. Synonym: fasciculus longitudinalis medialis, Collier's tract, medial longitudinal bundle, posterior longitudinal bundle. (05 Mar 2000) |
| Meynert's retroflex bundle | A compact bundle of fibres arising in the habenula and passing ventralward to the interpeduncular nucleus at the base of the midbrain; part of its fibres bypass this nucleus and terminate in the raphe nuclei of the caudal mesencephalic tegmentum. Synonym: fasciculus retroflexus, habenulointerpeduncular tract, Meynert's fasciculus, Meynert's retroflex bundle. (05 Mar 2000) |
| Pick's bundle | A bundle of nerve fibres recurving rostralward from the pyramidal tract in the medulla oblongata, and believed to consist of corticonuclear fibres. (05 Mar 2000) |
| Monakow's bundle | A somatotopically organised fibre bundle, relatively small in humans, arising from the red nucleus, immediately crossing in the ventral tegmental decussation, descending near the lateral surface of the brainstem into the lateral funiculus of the spinal cord at the ventral border of the lateral pyramidal tract. It terminates in the zona intermedia of the spinal cord where its distribution coincides with that of the lateral pyramidal tract; in contrast to the latter it appears not to have direct connections with spinal motor neurons. Impulses conveyed by this tract indirectly increase flexor muscle tone. Synonym: tractus rubrospinalis, Monakow's bundle, Monakow's tract, prepyramidal tract. (05 Mar 2000) |
| comma bundle of Schultze | A compact bundle composed of descending branches of posterior root fibres located near the border between the fasciculi gracilis and cuneatus of the cervical and thoracic spinal cord; it corresponds to the septomarginal fasciculus, Hoche's tract, or oval area of Flechsig in the lumbar, and to the triangle of Philippe-Gombault in the sacral spinal segments; like these, it can be demonstrated only in cases of demyelination resulting from dorsal root lesions. Synonym: fasciculus semilunaris, fasciculus interfascicularis, comma bundle of Schultze, comma tract of Schultze, interfascicular fasciculus. (05 Mar 2000) |
| muscle bundle | A group of muscle fibres ensheathed by connective tissue (perimysium). (05 Mar 2000) |
| posterior longitudinal bundle | A longitudinal bundle of fibres extending from the upper border of the mesencephalon into the cervical segments of the spinal cord, located close to the midline and ventral to the central gray matter; it is composed largely of fibres from the vestibular nuclei ascending to the motor neurons innervating the external eye muscles (abducens, trochlear, and oculomotor nuclei), and descending to spinal cord segments innervating the musculature of the neck. Synonym: fasciculus longitudinalis medialis, Collier's tract, medial longitudinal bundle, posterior longitudinal bundle. (05 Mar 2000) |
| precommissural bundle | See: olfactory bundle. (05 Mar 2000) |
| predorsal bundle | A bundle of thick, heavily myelinated fibres originating in the deep layers of the superior colliculus, crossing to the opposite side in the dorsal tegmental decussation, descending along the median plane, between the medial longitudinal fasciculus dorsally, the medial lemniscus ventrally, into the anterior funiculus of the spinal cord. The tract ends in the medial region of the anterior horn of the cervical spinal cord, and appears to be involved in head movements during visual and auditory tracking. Throughout its course in the brainstem it is accompanied by fibres of the tectobulbar tract. Synonym: tractus tectospinalis, Held's bundle, Loewenthal's bundle, Loewenthal's tract, Marchi's tract, predorsal bundle. (05 Mar 2000) |
| Held's bundle | A bundle of thick, heavily myelinated fibres originating in the deep layers of the superior colliculus, crossing to the opposite side in the dorsal tegmental decussation, descending along the median plane, between the medial longitudinal fasciculus dorsally, the medial lemniscus ventrally, into the anterior funiculus of the spinal cord. The tract ends in the medial region of the anterior horn of the cervical spinal cord, and appears to be involved in head movements during visual and auditory tracking. Throughout its course in the brainstem it is accompanied by fibres of the tectobulbar tract. Synonym: tractus tectospinalis, Held's bundle, Loewenthal's bundle, Loewenthal's tract, Marchi's tract, predorsal bundle. (05 Mar 2000) |
| Helie's bundle | A vertically arched bundle of fibres in the superficial layer of the myometrium. (05 Mar 2000) |
| Helweg's bundle | A slender bundle of nerve fibres in the peripheral zone of the lateral funiculus of the spinal cord, composed of spino-olivary fibres more likely than olivospinal fibres. Synonym: Helweg's bundle. (05 Mar 2000) |
| Schutz' bundle | A bundle of thin, poorly myelinated nerve fibres reciprocally connecting the periventricular zone of the hypothalamus with ventral parts of the central gray substance of the midbrain. Synonym: fasciculus longitudinalis dorsalis, Schutz' bundle, tract of Schutz. (05 Mar 2000) |
| His bundle electrogram | An electrogram recorded from the His bundle, either in the experimental animal or in man during cardiac catheterization. (05 Mar 2000) |