Ventral cochlear nucleus

Ventral cochlear nucleus
	Ventral cochlear nucleus is No. 3, at upper left
Details
Identifiers
Latin	nucleus cochlearis anterior
NeuroNames	722
NeuroLex ID	birnlex_2567
TA	A14.1.04.249
FMA	54621
	Anatomical terms of neuroanatomy [ edit on Wikidata]

Last updated April 08, 2019

In the ventral cochlear nucleus (VCN), auditory nerve fibers enter the brain via the nerve root in the VCN. The ventral cochlear nucleus is divided into the anterior ventral (anteroventral) cochlear nucleus (AVCN) and the posterior ventral (posteroventral) cochlear nucleus (PVCN). In the VCN, auditory nerve fibers bifurcate, the ascending branch innervates the AVCN and the descending branch innervates the PVCN and then continue to the dorsal cochlear nucleus. The orderly innervation by auditory nerve fibers gives the AVCN a tonotopic organization along the dorsoventral axis. Fibers that carry information from the apex of the cochlea that are tuned to low frequencies contact neurons in the ventral part of the AVCN; those that carry information from the base of the cochlea that are tuned to high frequencies contact neurons in the dorsal part of the AVCN. Several populations of neurons populate the AVCN. Bushy cells receive input from auditory nerve fibers through particularly large endings called end bulbs of Held. They contact stellate cells through more conventional boutons.

A nerve root is the initial segment of a nerve leaving the central nervous system. Types include:

The dorsal cochlear nucleus, is a cortex-like structure on the dorso-lateral surface of the brainstem. Along with the ventral cochlear nucleus (VCN), it forms the cochlear nucleus (CN), where all auditory nerve fibers from the cochlea form their first synapses.

Bushy cells are two types of second order neuron found in the anterior part of the ventral cochlear nucleus, the AVCN. They can be globular or spherical giving outputs to different parts of the superior olivary complex.

Cell types

The anterior cochlear nucleus contains several cell types, which correspond fairly well with different physiological unit types. Additionally, these cell types generally have specific projection patterns.

Bushy cells

Named due to the branching, tree-like, nature of their dendritic fields, visible using Golgi's method, they receive large end bulbs of Held from auditory nerve fibers. Bushy cells are of three subtypes that project to different target nuclei in the superior olivary complex.

Golgi's method is a silver staining technique that is used to visualize nervous tissue under light microscopy. The method was discovered by Camillo Golgi, an Italian physician and scientist, who published the first picture made with the technique in 1873. It was initially named the black reaction by Golgi, but it became better known as the Golgi stain or later, Golgi method.

The Calyx of Held is a particularly large synapse in the mammalian auditory central nervous system, so named by Hans Held in his 1893 article Die centrale Gehörleitung because of its resemblance to the calyx of a flower. Globular bushy cells in the anteroventral cochlear nucleus (AVCN) send axons to the contralateral medial nucleus of the trapezoid body (MNTB), where they synapse via these calyces on MNTB principal cells. These principal cells then project to the ipsilateral lateral superior olive (LSO), where they inhibit postsynaptic neurons and provide a basis for interaural level detection (ILD), required for high frequency sound localization. This synapse has been described as the largest in the brain.

Globular

Globular bushy cells project large axons to the contralateral medial nucleus of the trapezoid body (MNTB), in the superior olivary complex where they synapse onto principal cells via a single calyx of Held, and several smaller collaterals synapse ipsilaterally in the posterior (PPO) and dorsolateral periolivary (DLPO) nuclei, lateral superior olive (LSO), and lateral nucleus of the trapezoid body (LNTB); contralaterally in the dorsomedial periolivary nucleus (DMPO), ventral nucleus of the trapezoid body (VNTB), nucleus paragigantocellularis lateralis (PGL), and ventral nucleus of the lateral lemniscus (VNLL). Axons always send a collateral into the MNTB, but do not necessarily give rise to collaterals that innervate each of the other nuclei.^[1]

The trapezoid body is part of the auditory pathway where some of the axons coming from the cochlear nucleus decussate to the other side before traveling on to the superior olivary nucleus. This is believed to help with localization of sound.

Superior olivary complex collection of brainstem nuclei related to hearing

The superior olivary complex is a collection of brainstem nuclei that functions in multiple aspects of hearing and is an important component of the ascending and descending auditory pathways of the auditory system. The SOC is intimately related to the trapezoid body: most of the cell groups of the SOC are dorsal to this axon bundle while a number of cell groups are embedded in the trapezoid body. Overall, the SOC displays a significant interspecies variation, being largest in bats and rodents and smaller in primates.

Large spherical

Spherical bushy cells project ipsilaterally to the LSO, bilaterally to the medial superior olive (MSO) and LNTB, and contralaterally to the VNTB and VNLL. The most important purpose of these projections seems to be to imbue the MSO and LSO with their interaural time and level sensitivities (respectively).^[2]

Small spherical

Small spherical bushy cells likely project to the ipsilateral lateral superior olive. They project neither to the medial superior olives or to the medial nucleus of the trapezoid body.

Multipolar (stellate) cells

Multipolar cells fall into two distinct groups. Those whose axons project out of the aVCN through the trapezoid body, T stellate cells, have longer dendrites than bushy cells that characteristically lie in line with fascicles of auditory nerve fibers. These principal cells are excitatory.

Another name for these cells is 'choppers'. They have an intrinsical rhythm, and will fire action potentials with this rhythm once activated by the right sound.

Anterior ventral cochlear nucleus (AVCN)

The anteroventral cochlear nucleus (AVCN) (or accessory), is placed between the two divisions of the cochlear nerve, and is on the ventral aspect of the inferior peduncle.

The cochlear nerve is one of two parts of the vestibulocochlear nerve, a cranial nerve present in amniotes, the other part being the vestibular nerve. The cochlear nerve carries auditory sensory information from the cochlea of the inner ear directly to the brain. The other portion of the vestibulocochlear nerve is the vestibular nerve, which carries spatial orientation information to the brain from the semicircular canals, also known as semicircular ducts.

The AVCN can be subdivided based upon the cytoarchitecture of the region.
- Typical subdivisions are defined as: anterior (AaVCN), posterior (PaVCN), posterodorsal (PDaVCN), and posteroventral (PVaVCN).^[3]
A well-defined tonotopy is evident.^[4] Lateral PVaVCN, medial PVaVCN, and medial PDaVCN roughly correspond to the low (<1 kHz), middle (4–8 kHz), and high (>16 kHz) frequency regions defined by Bourk.^[3]
The aVCN projects to nearly all brainstem auditory structures. High frequency regions tend to project contralaterally, and low frequency regions bilaterally, preserving the tonotopic organization of the ascending auditory pathway.^[3]
Stellate/multipolar cells form the projection to both inferior colliculi (central nucleus and dorsal cortex), and synapse in a banded pattern, following the tonotopy of the region.^[3]

Cytoarchitecture, also known as cytoarchitectonics, is the study of the cellular composition of the central nervous system's tissues under the microscope. Cytoarchitectonics is one of the ways to parse the brain, by obtaining sections of the brain using a microtome and staining them with chemical agents which reveal where different neurons are located.

In physiology, tonotopy is the spatial arrangement of where sounds of different frequency are processed in the brain. Tones close to each other in terms of frequency are represented in topologically neighbouring regions in the brain. Tonotopic maps are a particular case of topographic organization, similar to retinotopy in the visual system.

Related Research Articles

Articles related to anatomy include:

The auditory system is the sensory system for the sense of hearing. It includes both the sensory organs and the auditory parts of the sensory system.

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 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.

The inferior colliculus (IC) is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex. The inferior colliculus has three subdivisions: the central nucleus, a dorsal cortex by which it is surrounded, and an external cortex which is located laterally. Its bimodal neurons are implicated in auditory-somatosensory interaction, receiving projections from somatosensory nuclei. This multisensory integration may underlie a filtering of self-effected sounds from vocalization, chewing, or respiration activities.

A koniocellular cell is a neuron with a small cell body that is located in the koniocellular layer of the lateral geniculate nucleus (LGN) in primates, including humans.

The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.

Cochlear nucleus Wikimedia disambiguation page

The cochlear nuclear (CN) complex comprises two cranial nerve nuclei in the human brainstem, the ventral cochlear nucleus (VCN) and the dorsal cochlear nucleus (DCN). The ventral cochlear nucleus is unlayered whereas the dorsal cochlear nucleus is layered. Auditory nerve fibers, fibers that travel through the auditory nerve carry information from the inner ear, the cochlea, on the same side of the head, to the nerve root in the ventral cochlear nucleus. At the nerve root the fibers branch to innervate the ventral cochlear nucleus and the deep layer of the dorsal cochlear nucleus. All acoustic information thus enters the brain through the cochlear nuclei, where the processing of acoustic information begins. The outputs from the cochlear nuclei are received in higher regions of the auditory brainstem.

The interaural time difference when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localization of sounds, as it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one side, the signal has further to travel to reach the far ear than the near ear. This pathlength difference results in a time difference between the sound's arrivals at the ears, which is detected and aids the process of identifying the direction of sound source.

The posterior thoracic nucleus, is a group of interneurons found in the medial part of lamina VII, also known as the intermediate zone, of the spinal cord. It is mainly located from the cervical vertebra C8 to lumbar L3-L4 levels and is an important structure for proprioception of the lower limb.

Binaural fusion or binaural integration is a cognitive process that involves the "fusion" of different auditory information presented binaurally, or to each ear. In humans, this process is essential in understanding speech as one ear may pick up more information about the speech stimuli than the other.

The olivocochlear system is a component of the auditory system involved with the descending control of the cochlea. Its nerve fibres, the olivocochlear bundle (OCB), form part of the vestibulocochlear nerve, and project from the superior olivary complex in the brainstem (pons) to the cochlea.

Most owls are nocturnal or crepuscular birds of prey. Because they hunt at night, they must rely on non-visual senses. Experiments by Roger Payne have shown that owls are sensitive to the sounds made by their prey, not the heat or the smell. In fact, the sound cues are both necessary and sufficient for localization of mice from a distant location where they are perched. For this to work, the owls must be able to accurately localize both the azimuth and the elevation of the sound source.

References

This article incorporates text in the public domain from page 788 of the 20th edition of Gray's Anatomy (1918)

↑ Smith, P. H., P. X. Joris, et al. (1991). "Projections of physiologically characterized globular bushy cell axons from the cochlear nucleus of the cat." J Comp Neurol 304(3): 387–407.
↑ Smith, P. H., P. X. Joris, et al. (1993). "Projections of physiologically characterized spherical bushy cell axons from the cochlear nucleus of the cat: evidence for delay lines to the medial superior olive." J Comp Neurol 331(2): 245–60.
1 2 3 4 Oliver, D. L. (1987). "Projections to the inferior colliculus from the anteroventral cochlear nucleus in the cat: possible substrates for binaural interaction." J Comp Neurol 264(1): 24–46.
↑ Bourk, T. R., J. P. Mielcarz, et al. (1981). "Tonotopic organization of the anteroventral cochlear nucleus of the cat." Hear Res 4(3-4): 215–41.

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[1] Smith, P. H., P. X. Joris, et al. (1991). "Projections of physiologically characterized globular bushy cell axons from the cochlear nucleus of the cat." J Comp Neurol 304(3): 387–407.

[2] Smith, P. H., P. X. Joris, et al. (1993). "Projections of physiologically characterized spherical bushy cell axons from the cochlear nucleus of the cat: evidence for delay lines to the medial superior olive." J Comp Neurol 331(2): 245–60.

[R1-3] 1 2 3 4 Oliver, D. L. (1987). "Projections to the inferior colliculus from the anteroventral cochlear nucleus in the cat: possible substrates for binaural interaction." J Comp Neurol 264(1): 24–46.

[4] Bourk, T. R., J. P. Mielcarz, et al. (1981). "Tonotopic organization of the anteroventral cochlear nucleus of the cat." Hear Res 4(3-4): 215–41.