Calyx of Held Calyx of Held The Calyx of Held is a particularly large synapse in the mammalian auditory central nervous system, so named by Hans Held 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
Calyx of Held MNTB neurons to reach the SOC approximately 0.2 ms following the initial cochlear excitation. This ~0.2 second time measurement is important for comparing the contralateral (opposite side) and ipsilateral (same side) stimulation necessary in sound localization in the horizontal plane, and is key in distinguishing the location of low frequency sounds. For every principal neuron there is one calyx, and for most GBC axons there is only a single calyx, although there are exceptions to this pairing. This in general creates a one-to-one ratio between GBCs, the calyces of Held, and the principal neurons. The calyx of Held encompasses the