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. 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. These principle 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 high frequency sound localization. This synapse has been described as the largest in the brain, 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.