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 sensitivity. Both low-threshold K channels and high-threshold delayed rectifier-type K channels are present in presynaptic neurons. There are four low-threshold K channels present: K1.1, K1.2, K1.3, and K7.5. K1.1 and K1.2 are located in the transition zone between the axon and the terminal, while K1.3 K7.5 are located in the calyx. There is a calcium activated potassium channel expressed in the calyx, however this type of channel does not contribute to neurotransmitter release. Within the span of one week, mice subjects (P7 to P14) showed that the density of the K1 and K3 low threshold channels increases, which in turn