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Structure and Projections of the Cochlear Nucleus
- Cochlear nuclei are located at the dorso-lateral side of the brainstem, spanning the junction of the pons and medulla.
- The ventral cochlear nucleus (VCN) is 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).
- The major input to the cochlear nucleus is from the auditory nerve, a part of cranial nerve VIII.
- Axons from the lower frequencies innervate the ventrolateral portions of the VCN and lateral-ventral portions of the DCN.
- Axons from the higher frequency organ of corti hair cells project to the dorsal portion of the VCN and dorsal-medial portions of the DCN.
- The tonotopic organization established in the cochlea is preserved in the cochlear nuclei.
- The DCN receives input not only from the auditory nerve but also from neurons in the VCN.
- Three major fiber bundles carry information from the cochlear nuclei to targets mainly on the opposite side of the brain.
- One projection goes to the contralateral superior olivary complex via the trapezoid body, while the other half shoots to the ipsilateral superior olivary complex.
- The dorsal acoustic stria rises above the medulla into the pons and hits the nuclei of the lateral lemniscus.
- The intermediate acoustic stria decussates across the medulla before joining the contralateral lateral lemniscus.
- Most of these inputs terminate in the inferior colliculus, although there are a few small projections to other forebrain structures.
Histology of the Cochlear Nucleus
- 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 and project to the ipsilateral and contralateral medial superior olive.
- Stellate cells, also known as multipolar cells, have longer dendrites that lie parallel to fascicles of auditory nerve fibers.
- Bushy cells receive input from multiple auditory nerve fibers and can improve the precision of timing information.
- Stellate cells play a role in processing auditory information.
Other Functions of the Cochlear Nucleus
- The cochlear nuclei have long been thought to receive input only from the ipsilateral ear, but there is evidence for stimulation from the contralateral ear via the contralateral cochlear nucleus.
- The cochlear nuclei also receive acoustic input from neurons in the ventral cochlear nucleus.
- There are projections to the somatosensory parts of the brain from the cochlear nuclei.
- The outputs from the cochlear nuclei are received in higher regions of the auditory brainstem.
- The processing of acoustic information begins in the cochlear nuclei.
Stellate Cells
- Also known as chopper cells
- Fire a regularly spaced train of action potentials
- Firing rate depends on the strength of the auditory input
- Narrowly tuned and have inhibitory sidebands
- Encode the spectrum of sounds and enhance spectral peaks and valleys
Octopus Cells, Principal Cells, Fusiform Cells, and Giant Cells
- Octopus Cells: Found in the posterior ventral cochlear nucleus (PVCN), have long, thick, tentacle-shaped dendrites, produce an Onset Response to tonal stimuli, can fire with high temporal precision, can respond to click trains at a rate of 800Hz.
- Principal Cells: Two types convey information out of the dorsal cochlear nucleus (DCN), receive acoustic input from auditory nerve fibers and stellate cells, acoustic input is also conveyed through inhibitory interneurons, receive sensory information about the location of the head and ears, distributed through a cerebellar-like circuit.
- Fusiform Cells: Also known as pyramidal cells, integrate information through apical and basal dendrites, receive multisensory, excitatory, and inhibitory input, enable analysis of spectral cues for sound localization, important when hearing is lost in one ear.
- Giant Cells: Integrate inputs from the molecular and deep layers, role in hearing is unclear, input from the deep layer is predominant.
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 (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.
| 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.
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| 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 | |
