Cochlear nucleus

Cochlear nuclei
Cochlear nuclei
	Dissection of brainstem. Dorsal view. ("Cochlear nucleus" is labeled on left, fifth from the bottom.)
	Terminal nuclei of the cochlear nerve, with their upper connections. (Schematic.) The vestibular nerve with its terminal nuclei and their efferent fibers have been suppressed. On the other hand, in order not to obscure the trapezoid body, the efferent fibers of the terminal nuclei on the right side have been resected in a considerable portion of their extent. The trapezoid body, therefore, shows only one-half of its fibers, viz., those that come from the left. Vestibular nerve, divided at its entrance into the medulla oblongata ; Cochlear nerve ; Accessory nucleus of acoustic nerve ; Tuberculum acusticum ; Efferent fibers of accessory nucleus ; Efferent fibers of tuberculum acusticum, forming the striae medullares, with 6’, their direct bundle going to the superior olivary nucleus of the same side; 6’’, their decussating bundles going to the superior olivary nucleus of the opposite side; Superior olivary nucleus ; Trapezoid body ; Trapezoid nucleus ; Central acoustic tract (lateral lemniscus); Raphé ; Pyramidal tracts ; Fourth ventricle ; Inferior peduncle ;
Details
Part of	Brainstem
System	Auditory system
Artery	AICA
Identifiers
Latin	nuclei cochleares
MeSH	D017626
NeuroNames	720
NeuroLex ID	birnlex_1151
TA98	A14.1.04.247 ; A14.1.05.430
TA2	6006, 6007
FMA	72240
	Anatomical terms of neuroanatomy [ edit on Wikidata]

Last updated November 09, 2024

The cochlear nucleus (CN) or cochlear nuclear 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 (also known as the cochlear nerve or eighth cranial 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.

Structure

The cochlear nuclei (CN) are located at the dorso-lateral side of the brainstem, spanning the junction of the pons and medulla.

The ventral cochlear nucleus (VCN) on the ventral aspect of the brain stem, ventrolateral to the inferior peduncle.
The dorsal cochlear nucleus (DCN), also known as the tuberculum acusticum or acoustic tubercle, curves over the VCN and wraps around the cerebellar peduncle.
- The VCN is further divided by the nerve root into the posteroventral cochlear nucleus (PVCN) and the anteroventral cochlear nucleus (AVCN).^[1]

Projections to the cochlear nuclei

The major input to the cochlear nucleus is from the auditory nerve, a part of cranial nerve VIII (the vestibulocochlear nerve). The auditory nerve fibers form a highly organized system of connections according to their peripheral innervation of the cochlea. Axons from the spiral ganglion cells of the lower frequencies innervate the ventrolateral portions of the ventral cochlear nucleus and lateral-ventral portions of the dorsal cochlear nucleus. The axons from the higher frequency organ of corti hair cells project to the dorsal portion of the ventral cochlear nucleus and the dorsal-medial portions of the dorsal cochlear nucleus. The mid frequency projections end up in between the two extremes; in this way the tonotopic organization that is established in the cochlea is preserved in the cochlear nuclei. This tonotopic organization is preserved because only a few inner hair cells synapse on the dendrites of a nerve cell in the spiral ganglion, and the axon from that nerve cell synapses on only a very few dendrites in the cochlear nucleus. In contrast with the VCN that receives all acoustic input from the auditory nerve, the DCN receives input not only from the auditory nerve but it also receives acoustic input from neurons in the VCN (T stellate cells). The DCN is therefore in a sense a second order sensory nucleus.

The cochlear nuclei have long been thought to receive input only from the ipsilateral ear. There is evidence, however, for stimulation from the contralateral ear via the contralateral CN,^[2] and also the somatosensory parts of the brain.^[3]

Projections from the cochlear nuclei

There are three major fiber bundles, axons of cochlear nuclear neurons, that carry information from the cochlear nuclei to targets that are mainly on the opposite side of the brain. Through the medulla, one projection goes to the contralateral superior olivary complex (SOC) via the trapezoid body, whilst the other half shoots to the ipsilateral SOC. This pathway is called the ventral acoustic stria (VAS or, more commonly, the trapezoid body). Another pathway, called the dorsal acoustic stria (DAS, also known as the stria of von Monakow), rises above the medulla into the pons where it hits the nuclei of the lateral lemniscus along with its kin, the intermediate acoustic stria (IAS, also known as the stria of Held). The IAS decussates across the medulla, before joining the ascending fibers in the contralateral lateral lemniscus. The lateral lemniscus contains cells of the nuclei of the lateral lemniscus, and in turn projects to the inferior colliculus. The inferior colliculus receives direct, monosynaptic projections from the superior olivary complex, the contralateral dorsal acoustic stria, some classes of stellate neurons of the VCN, as well as from the different nuclei of the lateral lemniscus.

Most of these inputs terminate in the inferior colliculus, although there are a few small projections that bypass the inferior colliculus and project to the medial geniculate, or other forebrain structures.

Medial superior olive (MSO) via trapezoid body (TB) – Ipsilateral and contralateral stimulation for low frequency sounds.
Lateral superior olive (LSO) directly and via TB – Ipsilateral stimulation for high frequency sounds.
Medial nucleus of trapezoid body (MNTB) – Contralateral stimulation.
Inferior colliculus – Contralateral stimulation.
Periolivary nuclei (PON) – Ipsilateral and contralateral stimulation.
Lateral lemniscus (LL) and lemniscal nuclei (LN) – Ipsilateral and contralateral stimulation.

Histology

Three types of principal cells convey information out of the ventral cochlear nucleus: Bushy cells, stellate cells, and octopus cells.

Bushy cells are found mainly in the anterior ventral cochlear nucleus (AVCN). These can be further divided into large spherical, small spherical and globular bushy cells, depending on their appearance, and also their location. Within the AVCN there is an area of large spherical cells; caudal to this are smaller spherical cells, and globular cells occupy the region around the nerve root. An important difference between these subtypes is that they project to differing targets in the superior olivary complex. Large spherical bushy cells project to the ipsilateral and contralateral medial superior olive. Globular bushy cells project to the contralateral medial nucleus of the trapezoid body, and small spherical bushy cells likely project to the lateral superior olive. They have a few (1-4) very short dendrites with numerous small branching, which cause it to resemble a “bush”. The bushy cells have specialized electrical properties that allow them to transmit timing information from the auditory nerve to more central areas of the auditory system. Because bushy cells receive input from multiple auditory nerve fibers that are tuned to similar frequencies, bushy cells can improve the precision of the timing information by in essence averaging out jitter in timing of the inputs. Bushy cells can also be inhibited by sounds adjacent to the frequency to which they are tuned, leading to even sharper tuning than seen in auditory nerve fibers. These cells are usually innervated only by a few auditory nerve fibres, which dominate its firing pattern. These afferent nerve fibres wrap their terminal branches around the entire soma, creating a large synapse onto the bushy cells, called an "endbulb of Held". Therefore, a single unit recording of an electrically stimulated bushy neuron characteristically produces exactly one action potential and constitutes the primary response.
Stellate cells (aka multipolar cells), have longer dendrites that lie parallel to fascicles of auditory nerve fibers. They are also called chopper cells, in reference to their ability to fire a regularly spaced train of action potentials for the duration of a tonal or noise stimulus. The chopping pattern is intrinsic to the electrical excitability of the stellate cell, and the firing rate depends on the strength of the auditory input more than on the frequency. Each stellate cell is narrowly tuned and has inhibitory sidebands, enabling the population of stellate cells to encode the spectrum of sounds, enhancing spectral peaks and valleys. These neurons provide acoustic input to the DCN.
Octopus cells are found in a small region of the posterior ventral cochlear nucleus (PVCN). The distinguishing features of these cells are their long, thick and tentacle-shaped dendrites that typically emanate from one side of the cell body. Octopus cells produce an "Onset Response" to simple tonal stimuli. That is, they respond only at the onset of a broad-band stimulus. The octopus cells can fire with some of the highest temporal precision of any neuron in the brain. Electrical stimuli to the auditory nerve evoke a graded excitatory postsynaptic potential in the octopus cells. These EPSPs are very brief. The octopus cells are thought to be important for extracting timing information. It has been reported that these cells can respond to click trains at a rate of 800 Hz.

Two types of principal cells convey information out of the dorsal cochlear nucleus (DCN) to the contralateral inferior colliculus. The principal cells receive two systems of inputs. Acoustic input comes to the deep layer through several paths. Excitatory acoustic input comes from auditory nerve fibers and also from stellate cells of the VCN. Acoustic input is also conveyed through inhibitory interneurons (tuberculoventral cells of the DCN and "wide band inhibitors" in the VCN). Through the outermost molecular layer, the DCN receives other types of sensory information, most importantly information about the location of the head and ears, through parallel fibers. This information is distributed through a cerebellar like circuit that also includes inhibitory interneurons.

Fusiform cells (also known as pyramidal cells). Fusiform cells integrate information through two tufts of dendrites, the apical dendrites receiving multisensory, excitatory and inhibitory input through the outermost molecular layer and the basal dendrites receiving excitatory and inhibitory acoustic input from the basal dendrites that extend into the deep layer. These neurons are thought to enable mammals to analyze the spectral cues that enable us to localize sounds in elevation and when we lose hearing in one ear.
Giant cells also integrate inputs from the molecular and deep layers but input from the deep layer is predominant. It is unclear what their role is in hearing.

Function

The cochlear nuclear complex is the first integrative, or processing, stage in the auditory system ^[4]. Information is brought to the nuclei from the ipsilateral cochlea via the cochlear nerve ^[5]. Several tasks are performed in the cochlear nuclei. By distributing acoustic input to multiple types of principal cells, the auditory pathway is subdivided into parallel ascending pathways, which can simultaneously extract different types of information. The cells of the ventral cochlear nucleus extract information that is carried by the auditory nerve in the timing of firing and in the pattern of activation of the population of auditory nerve fibers. The cells of the dorsal cochlear nucleus perform a non-linear spectral analysis and place that spectral analysis into the context of the location of the head, ears and shoulders and that separate expected, self-generated spectral cues from more interesting, unexpected spectral cues using input from the auditory cortex, pontine nuclei, trigeminal ganglion and nucleus, dorsal column nuclei and the second dorsal root ganglion. It is likely that these neurons help mammals to use spectral cues for orienting toward those sounds. The information is used by higher brainstem regions to achieve further computational objectives (such as sound source location or improvement in signal-to-noise ratio). The inputs from these other areas of the brain probably play a role in sound localization.

In order to understand in more detail the specific functions of the cochlear nuclei it is first necessary to understand the way sound information is represented by the fibers of the auditory nerve. Briefly, there are around 30,000 auditory nerve fibres in each of the two auditory nerves. Each fiber is an axon of a spiral ganglion cell that represents a particular frequency of sound, and a particular range of loudness. Information in each nerve fibre is represented by the rate of action potentials as well as the particular timing of individual action potentials. The particular physiology and morphology of each cochlear nucleus cell type enhances different aspects of sound information.

Additional images

Dissection of brain-stem. Lateral view.
The cranial nerve nuclei schematically represented; dorsal view. Motor nuclei in red; sensory in blue.
Primary terminal nuclei of the afferent (sensory) cranial nerves schematically represented; lateral view.
Scheme showing the course of the fibers of the lemniscus; medial lemniscus in blue, lateral in red.
Cross section of lower pons showing the cochlear nucleus (#1) labeled at the top right.

Related Research Articles

Articles related to anatomy include:

The brainstem is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is continuous with the thalamus of the diencephalon through the tentorial notch, and sometimes the diencephalon is included in the brainstem.

<span class="mw-page-title-main">Lateral geniculate nucleus</span> Component of the visual system in the brains thalamus

In neuroanatomy, the lateral geniculate nucleus is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve. There are two LGNs, one on the left and another on the right side of the thalamus. In humans, both LGNs have six layers of neurons alternating with optic fibers.

The spinothalamic tract is a nerve tract in the anterolateral system in the spinal cord. This tract is an ascending sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cortex of the postcentral gyrus.

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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 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.

<span class="mw-page-title-main">Pretectal area</span> Structure in the midbrain which mediates responses to ambient light

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<span class="mw-page-title-main">Trapezoid body</span> Part of the auditory pathway

The trapezoid body or ventral acoustic stria is a structure in the pontine tegmentum formed by the crossing-over (decussation) of a portion of the efferent second-order fibers of the ventral cochlear nucleus. After decussating, some of these fibres proceed to ascend in the contralateral lateral lemniscus to reach and terminate in the dorsal nucleus of lateral lemniscus, and inferior colliculus.

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<span class="mw-page-title-main">Medial geniculate nucleus</span>

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<span class="mw-page-title-main">Cochlear nerve</span> Nerve carrying auditory information from the inner ear to the brain

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.

<span class="mw-page-title-main">Facial motor nucleus</span>

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<span class="mw-page-title-main">Dorsal cochlear nucleus</span>

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.

<span class="mw-page-title-main">Superior olivary complex</span> Collection of brainstem nuclei related to hearing

The superior olivary complex (SOC) or superior olive is a collection of brainstem nuclei that is located in pons, 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.

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.

Binaural fusion or binaural integration is a cognitive process that involves the combination of different auditory information presented binaurally, or to each ear. In humans, this process is essential in understanding speech in noisy and reverberent environments.

<span class="mw-page-title-main">Ventral cochlear nucleus</span>

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.

The calyx of Held is a particularly large excitatory synapse in the mammalian auditory nervous system, so named after Hans Held who first described it 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.

References

This article incorporates text in the public domain from page 788 of the 20th edition of Gray's Anatomy (1918)Young ED, Spirou GA, Rice JJ, Voigt HF (June 1992). "Neural organization and responses to complex stimuli in the dorsal cochlear nucleus". Philos. Trans. R. Soc. Lond. B Biol. Sci. 336 (1278): 407–13. doi:10.1098/rstb.1992.0076. PMID 1354382.

↑ Middlebrooks, J.C. (2009). "Auditory System: Central Pathways". In Squire (ed.). Encyclopedia of Neuroscience. Academic Press. pp. 745–752, here: p. 745 f.
↑ Davis KA (September 2005). "Contralateral effects and binaural interactions in dorsal cochlear nucleus". J. Assoc. Res. Otolaryngol. 6 (3): 280–96. doi:10.1007/s10162-005-0008-5. PMC 2504593 . PMID 16075189.
↑ Shore, S.E. (2009). "Auditory/Somatosensory Interactions". In Squire (ed.). Encyclopedia of Neuroscience. Academic Press. pp. 691–5.
↑ Quimby, Alexandra E.; Wei, Kimberly; Adewole, Dayo; Eliades, Steven; Cullen, D. Kacy; Brant, Jason A. (2023-11-03). "Signal processing and stimulation potential within the ascending auditory pathway: a review". Frontiers in Neuroscience. 17. doi: 10.3389/fnins.2023.1277627 . ISSN 1662-453X. PMC 10658786 . PMID 38027521.
↑ Peterson, Diana C.; Reddy, Vamsi; Launico, Marjorie V.; Hamel, Renee N. (2024), "Neuroanatomy, Auditory Pathway", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30335344 , retrieved 2024-11-08

External links

University of Buffalo at the Library of Congress Web Archives(archived 2001-11-27)
Illustration and text: Bs97/TEXT/P12/intro.htm at the University of Wisconsin-Madison Medical school
Medical research council Archived 2005-03-19 at the Wayback Machine
Shore lab

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[1] Middlebrooks, J.C. (2009). "Auditory System: Central Pathways". In Squire (ed.). Encyclopedia of Neuroscience. Academic Press. pp. 745–752, here: p. 745 f.

[2] Davis KA (September 2005). "Contralateral effects and binaural interactions in dorsal cochlear nucleus". J. Assoc. Res. Otolaryngol. 6 (3): 280–96. doi:10.1007/s10162-005-0008-5. PMC 2504593 . PMID 16075189.

[3] Shore, S.E. (2009). "Auditory/Somatosensory Interactions". In Squire (ed.). Encyclopedia of Neuroscience. Academic Press. pp. 691–5.

[4] Quimby, Alexandra E.; Wei, Kimberly; Adewole, Dayo; Eliades, Steven; Cullen, D. Kacy; Brant, Jason A. (2023-11-03). "Signal processing and stimulation potential within the ascending auditory pathway: a review". Frontiers in Neuroscience. 17. doi: 10.3389/fnins.2023.1277627 . ISSN 1662-453X. PMC 10658786 . PMID 38027521.

[5] Peterson, Diana C.; Reddy, Vamsi; Launico, Marjorie V.; Hamel, Renee N. (2024), "Neuroanatomy, Auditory Pathway", StatPearls, Treasure Island (FL): StatPearls Publishing, PMID 30335344 , retrieved 2024-11-08

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