science

Lateral lemniscus

Lateral lemniscus is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lateral lemniscus rather than just read about it. In short: 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.

Key takeaways

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Reference excerpt

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.

Connections There are three small nuclei on each of the lateral lemnisci:

the intermediate nucleus of the lateral lemniscus (INLL) the ventral nucleus of the lateral lemniscus (VNLL) the dorsal nucleus of the lateral lemniscus (DNLL) 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). The dorsal cochlear nucleus (DCN) has input from the LL and output to the contralateral LL via the ipsilateral and contralateral Dorsal Acoustic Stria. The two lemnisci communicate via the commissural fibers of Probst.

Nuclei of the lateral lemniscus 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.

DNLL 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. Two populations of GABA+ cells are visible: larger, lightly stained cells that project to the contralateral IC, and smaller, darker stained cells that project ipsilaterally. 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 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. GAD, GABA, and Glycine staining reveals several distinct regions that are not evident in standard cytoarchitectural preparations. 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. Most GABA+ cells are gly+ as well.[broken footnote]

VNLL Sound in the contralateral ear leads to the strongest responses in the VNLL, which deals with some temporary processing. The VNLL may also be essential to the IC’s decoding of amplitude modulated sounds. 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 columnar region contains many glycine-positive (0 GABA+) neurons, whereas the dorsal region contains clusters of GABA+ neurons intermingled with gly+ cells, with some cells containing both.

Inputs and outputs to nuclei The table below shows that each of the nuclei have a complicated arrangement of ipsilateral and contralateral afferent inputs and outputs:

Additional images

References This article incorporates text in the public domain from page 805 of the 20th edition of Gray's Anatomy (1918)

Illustrations

Worked examples

Example 1 — a first encounter with Lateral lemniscus

Start with the simplest possible case. Write down what Lateral lemniscus claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lateral lemniscus before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lateral lemniscus ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lateral lemniscus

In research: Lateral lemniscus appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lateral lemniscus in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lateral lemniscus is common in secondary-school and first-year university syllabi. It links to neighbouring topics Brainstem, so understanding it makes those chapters shorter.
In everyday life: Look for Lateral lemniscus outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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Frequently asked questions

What is Lateral lemniscus in simple terms?

Why does Lateral lemniscus matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lateral lemniscus?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

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It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lateral lemniscus.