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 causes an action potential to be triggered on the postsynaptic side – further encouraged by low internal sodium of the principal neurons. In the mature calyx, the AMPA receptors are concentrated on the principal neuron as to localize the transmission for greater action potential probability. Also note, the NMDA-type glutamate receptors contributions decrease after the onset of hearing. The mechanism behind synaptic vesicle endocytosis changes as the calyx becomes more mature. Calmodulin and calcineurin in their active form are required for vesicle endocytosis in an immature calyx; however, in the mature calyx neither calmodulin nor calcineurin are necessary. Rather, the