Anterior cochlear nucleus
|Brain: Anterior cochlear nucleus|
Anterior cochlear nucleus is No. 3, at upper left
|Latin||nucleus cochlearis anterior|
The anterior cochlear nucleus (or ventral or accessory), placed between the two divisions of the cochlear nerve, is on the ventral aspect of the inferior peduncle. Composed of several regions of distinct cell types, this nucleus serves primarily as a relay station for ascending auditory information. Bushy cells in the anterior ventral cochlear nucleus (AVCN), which receive end bulbs of Held from auditory nerve fibers, project to the superior olivary complex through the trapezoid body and intermediate acoustic stria. Other cell types project to the lateral lemniscus and the inferior colliculus directly.
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.
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. These cells can be further subdivided into spherical and globular types based upon their appearance in Nissl-stained material, and their location in the nucleus (anterior AVCN and posterior AVCN respectively).
Globular bushy cells project large axons to the contralateral MNTB 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.
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).
Octopus cells have thick dendrites, turning away from the nuclues, so forming 'legs' like those of an octopus. They project to the NLL (nuclei of the lateral leminiscus). The threshold for these cells is higher than that of the auditory nerve. They only fire an action potential at the start of a signal, and are sensitive for amplitude modulation.
Multipolar (stellate) cells
- These cells are formed like a star and project to the SOC (superior olive nucleus). They have a very fine tuning, caused by inhibitory signals. Certain signals with the frequency f and intensity I will activate the cells, whereas other combinations of f and I will inhibit activation.
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 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).
- A well-defined tonotopy is evident. 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.
Posterior Ventral Cochlear Nucleus (PVCN)
- Needs information added
- 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.
- 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.