- lemniscus
- A bundle of nerve fibers ascending from sensory relay nuclei to the thalamus. SYN: fillet (1). [L. from G. lemniskos, ribbon or fillet]- gustatory l. the uncrossed secondary-sensory fiber system ascending from the rhombencephalic gustatory nucleus to the parabrachial nuclei (rostral pontine level) and directly to the thalamic gustatory nucleus (ventral postero-medial nucleus, pars parvicellularis).- lateral l. [TA] a bundle of ascending fibers that originate from the cochlear and auditory relay nuclei of the rhombencephalon, enter the trapezoid body, a transverse fiber stratum in which about half their number decussate, and from here turn rostrally along the lateral side of the spinothalamic tract; in the midbrain, it arches dorsally and enters the inferior colliculus in which all of its fibers terminate; the auditory pathway is transsynaptically extended from here by the brachium of the inferior colliculus to the medial geniculate body of the thalamus, from which in turn the auditory radiation leads to the auditory cortex; intercalated in the trapezoid body and along the ascending trajectory of the l. are several cell groups in which part of the fibers synapse. SYN: l. lateralis [TA], acoustic l., auditory l., auditory tract, lateral fillet.- medial l. [TA] a band of white fibers originating from the gracile and cuneate nuclei and decussating in the lower medulla; thence it passes upward through the center of the medulla oblongata, close to the median raphe; on entering the pons it spreads out laterally to form a flat band ascending over the dorsal border of the pontine nuclei; in the mesencephalon it passes over the dorsal border of the substantia nigra and is displaced laterally by the red nucleus; passing medial to the medial geniculate body, the bundle enters and terminates in the ventral posterior nucleus of the thalamus. Throughout their course, the fibers retain a somatotopic order such that those originating from the gracile nucleus and representing the lower extremity lie lateral to those originating in the cuneate nucleus and representing the arm. The medial l. conveys somatic-sensory information involved in tactile discrimination (two-point discrimination), position sense, and vibration sense. SYN: l. medialis [TA], medial fillet, Reil band (2), Reil ribbon.- spinal l. [TA] SYN: spinothalamic tract.- l. spinalis [TA] SYN: spinothalamic tract.- trigeminal l. [TA] collective term denoting the fibers ascending from the sensory nuclei of the trigeminus; one such fiber system originates from the spinal trigeminal nucleus and from the principal sensory nucleus, decussates, and ascends as the anterior trigeminothalamic tract [TA] (ventral trigeminothalamic tract [TAalt]) in close association with the medial l. with which it enters the ventrobasal complex to terminate in the ventral posteromedial nucleus; a second, uncrossed, fiber group originating from the principal sensory nucleus that follows an ascending course through central parts of the mesencephalic tegmentum as the posterior trigeminothalamic tract [TA] (dorsal trigeminothalamic tract [TAalt]) also to terminate in the ventral posteromedial nucleus. The trigeminal l. conveys tactile, pain, and temperature impulses from the skin of the face, the mucous membranes of the nasal and oral cavities, and the eye, as well as proprioceptive information from the facial and masticatory muscles. SYN: l. trigeminalis [TA].- l. trigeminalis [TA] SYN: trigeminal l..
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lem·nis·cus lem-'nis-kəs n, pl -nis·ci -'nis-.(k)ī, -'nis-.kē a band of fibers and esp. nerve fibers called also fillet see LATERAL LEMNISCUS, MEDIAL LEMNISCUSlem·nis·cal -kəl adj* * *
n.a ribbon-like tract of nerve tissue conveying information from the spinal cord and brainstem upwards through the midbrain to the higher centres. On each side a medial lemniscus acts as a pathway from the spinal cord, while an outer lateral lemniscus commences higher up and is mainly concerned with hearing.* * *
lem·nis·cus (lem-nisґkəs) gen. and pl. lemnisґci [L., from Gr. lēmniskos ribbon] a ribbon or band. [TA] a band or bundle of sensory fibers in the central nervous system; called also fillet. See also bundle, fasciculus, tract, and tractus.
Medical dictionary. 2011.
