Calyx of Held

The Calyx of Held is a particularly large synapse in the mammalian auditory central nervous system, named by H. Held in his 1893 article "Die centrale Gehörleitung", due to its flower-petal like shape [Held, H."Die centrale Gehörleitung" Arch. Anat. Physiol. Anat. Abt, 1893] [Satzler, K., L. F. Sohl, et al. (2002). "Three-dimensional reconstruction of a calyx of Held and its postsynaptic principal neuron in the medial nucleus of the trapezoid body." J Neurosci 22(24): 10567-79.] . Globular bushy cells in the Ventral Cochlear Nucleus (VCN) send axons to the contralateral Medial Nucleus of the Trapezoid body (MNTB), where they synapse via these calyces on MNTB principle cells [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. (1998). "Anatomy and physiology of principal cells of the medial nucleus of the trapezoid body (MNTB) of the cat." J Neurophysiol 79(6): 3127-42.] . These principle cells then project to the ipsilateral Lateral Superior Olive (LSO) [Spangler, K. M., W. B. Warr, et al. (1985). "The projections of principal cells of the medial nucleus of the trapezoid body in the cat." J Comp Neurol 238(3): 249-62.] , where they inhibit postsynaptic neurons and provide a basis for interaural level detection (ILD), required for high frequency sound localization [Tsuchitani, C. (1997). "Input from the medial nucleus of trapezoid body to an interaural level detector." Hear Res 105(1-2): 211-24.] . This synapse has been described as the largest in the brain [Morest, D. K. (1968). "The collateral system of the medial nucleus of the trapezoid body of the cat, its neuronal architecture and relation to the olivo-cochlear bundle." Brain Res 9(2): 288-311.] , which hints at its importance. This structure is specially designed for fast, efficient transportation of information from one cell to the next.

The related end bulb of Held is a smaller synapse found in other auditory brainstem structures. As with the calyx, these synapses promote fast, efficient information transfer.

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