The medial lemniscus , also known as Reil's band or Reil's ribbon , is a large ascending bundle of heavily myelinated axons that decussate in the brainstem , specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of nucleus gracilis and nucleus cuneatus. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally. The medial lemniscus is part of the dorsal column—medial lemniscus pathway , which ascends from the skin to the thalamus ,  which is important for somatosensation from the skin and joints, therefore, lesion of the medial lemnisci causes an impairment of vibratory and touch-pressure sense. Lemniscus means "ribbon", so named because the medial lemniscus "spirals" or "turns" as it ascends.
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The lateral lemniscus is a tract of axons in the brainstem that carries information about sound from the cochlear nucleus to various brainstem nuclei and ultimately the contralateral inferior colliculus of the midbrain.
Three distinct, primarily inhibitory, cellular groups are located interspersed within these fibers, and are thus named the nuclei of the lateral lemniscus. Fibers leaving these brainstem nuclei ascending to the inferior colliculus rejoin the lateral lemniscus. In that sense, this is not a ' lemniscus ' in the true sense of the word second order, decussated sensory axons , as there is third and out of the lateral superior olive , fourth order information coming out of some of these brainstem nuclei.
The lateral lemniscus is located where the cochlear nuclei and the pontine reticular formation PRF crossover. The PRF descends the reticulospinal tract where it innervates motor neurons and spinal interneurons. It is the main auditory tract in the brainstem that connects the superior olivary complex SOC with the inferior colliculus IC. There are three small nuclei on each of the lateral lemnisci: the ventral, dorsal, and the intermediate.
The two lemnisci communicate via the commissural fibers of Probst. The function of the complex of Nuclei of the lateral lemniscus is not known; however it has good temporal resolution compared to other cells higher than the cochlear nuclei and is sensitive to both timing and amplitude changes in sound.
It is also involved in the acoustic startle reflex; the most likely region for this being the VNLL. The cells of the DNLL respond best to bilateral inputs, and have onset and complexity tuned sustained responses. The nucleus is primarily GABAergic,  and projects bilaterally to the inferior colliculus , and contralaterally to the DNLL, with different populations of cells projecting to each IC.
In rat, the DNLL has a prominent columnar organization. Nearly all neurons are stained for GABA, especially in the central part of the nucleus, and the remaining GABA negative cells are interspersed with the positive, and often stain for glycine. GABAergic axon terminals form dense groups surrounded by GABA-lemniscal fibers throughout the nucleus, and synapse on both somata and in the neuropil. Glycinergic axon terminals, on the other hand, are more finely localized, with the majority of recipient neurons located laterally in the nucleus.
INLL also has little spontaneous activity and broad tuning curves. The temporal responses are significantly different from cells of the VNLL. This structure is greatly hypertrophied in the rat, forming a prominent bulge on the surface of the brainstem. A modest number of GABA-stained neurons are arranged in small groups, generally in the center of the nucleus, whereas glycine-stained neurons are more common and widely dispersed, with regional concentrations in the dorsolateral and ventrolateral portions of the nucleus.
Sound in the contralateral ear leads to the strongest responses in the VNLL, which deals with some temporary processing. VNLL cells have little spontaneous activity, broad and moderately complex tuning curves; they have both phasic and tonic responses and are involved in temporal processing.
In rat, the VNLL is composed of two subdivisions, the ventral columnar and dorsal non columnar regions. The table below shows that each of the nuclei have a complicated arrangement of ipsilateral and contralateral afferent inputs and outputs: [ citation needed ]. Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red.
From Wikipedia, the free encyclopedia. Lateral lemniscus Lateral lemniscus in red, as it connects the cochlear nucleus , superior olivary nucleus and the inferior colliculus. Seen from behind. Mugnaini Merchan, et al. Larue, et al. Anatomy of the pons. Cerebellopontine angle Superior medullary velum Sulcus limitans Medial eminence Facial colliculus. Trapezoid body Trigeminal lemniscus Dorsal trigeminal tract Ventral trigeminal tract Medial lemniscus Lateral lemniscus Medial longitudinal fasciculus Vestibulo-oculomotor fibers Anterior trigeminothalamic tract Central tegmental tract.
Inferior cerebellar peduncle Vestibulocerebellar tract Medial longitudinal fasciculus Vestibulospinal tract Medial vestibulospinal tract Lateral vestibulospinal tract. Apneustic center Pneumotaxic center Parabrachial nuclei Subparabrachial nucleus Medial parabrachial nucleus Lateral parabrachial nucleus Superior olivary nucleus Locus coeruleus. Pontine nuclei. Basilar sulcus.
Anatomy of the midbrain. Corpora quadrigemina : Inferior colliculus Brachium Superior colliculus Brachium. Pretectal area. Spinotectal tract Central tegmental tract. Tectospinal tract. Periaqueductal gray Raphe nuclei dorsal. Ventral tegmental area Rostromedial tegmental nucleus Pedunculopontine nucleus.
Red nucleus Rostral interstitial nucleus of medial longitudinal fasciculus Parabrachial area. Interpeduncular nucleus Midbrain reticular formation. Cerebral aqueduct. Pars compacta Pars reticulata. Superior cerebellar peduncle Decussation Interpeduncular fossa. Physiology of balance and hearing.
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