In the ventral cochlear nucleus (VCN),

auditory nerve The cochlear nerve (also auditory nerve or acoustic 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 ...

fibers enter the brain via the

nerve root A nerve root (Latin: ''radix nervi'') is the initial segment of a nerve leaving the central nervous system. Nerve roots can be classified as: *Cranial nerve roots: the initial or proximal segment of one of the twelve pairs of cranial nerves leaving ...

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 dorsal cochlear nucleus (DCN, also known as the "tuberculum acusticum"), 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 au ...

. The orderly innervation by auditory nerve fibers gives the AVCN a

tonotopic In physiology, tonotopy (from Greek tono = frequency and topos = place) 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 ...

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 cell 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. Structure Bushy cel ...

s receive input from auditory nerve fibers through particularly large endings called end bulbs of Held. They contact

stellate cell Stellate cells are neurons in the central nervous system, named for their star-like shape formed by dendritic processes radiating from the cell body. Many stellate cells are GABAergic and are located in the molecular layer of the cerebellum. Ste ...

s through more conventional boutons.

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 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 ...

, 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.

Globular

Globular bushy cells project large axons to the contralateral medial nucleus of the

trapezoid body The trapezoid body (the ventral acoustic stria) is part of the auditory pathway where some of the axons coming from the cochlear nucleus (specifically, the anterior cochlear nucleus) decussate (cross over) to the other side before traveling on to ...

(MNTB), in the

superior olivary complex The superior olivary complex (SOC) or superior olive 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 SO ...

where they synapse onto principal cells via a single

calyx of Held The Calyx of Held is a particularly large synapse in the mammalian Auditory system, auditory central nervous system, so named after Hans Held who first described it in his 1893 article ''Die centrale Gehörleitung''Held, H. "Die centrale Gehörlei ...

, 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 Nucleus ( : nuclei) is a Latin word for the seed inside a fruit. It most often refers to: *Atomic nucleus, the very dense central region of an atom *Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA Nucle ...

(PGL), and

ventral nucleus of the lateral lemniscus 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 in ...

(VNLL). Axons always send a collateral into the MNTB, but do not necessarily give rise to collaterals that innervate each of the other nuclei.

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). 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 The cochlear nerve (also auditory nerve or acoustic 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 ...

, and is on the ventral aspect of the

inferior peduncle The upper part of the posterior district of the medulla oblongata is occupied by the inferior cerebellar peduncle, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and vagus nerv ...

. *The AVCN can be subdivided based upon the

cytoarchitecture Cytoarchitecture (Greek '' κύτος''= "cell" + '' ἀρχιτεκτονική''= "architecture"), also known as cytoarchitectonics, is the study of the cellular composition of the central nervous system's tissues under the microscope. Cytoarchi ...

of the region. **Typical subdivisions are defined as: anterior (AaVCN), posterior (PaVCN), posterodorsal (PDaVCN), and posteroventral (PVaVCN).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. *A well-defined

tonotopy In physiology, tonotopy (from Greek tono = frequency and topos = place) 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 ...

is evident.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. 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. *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. *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.

References

{{DEFAULTSORT:Anterior Cochlear Nucleus Auditory system Cranial nerve nuclei