second optic chiasma [FBbt_00003922]

second optic chiasma

ID: FBbt_00003922

Chiasma lying between the medulla and the lobula/lobula plate of the optic lobe (Ito et al., 2014). Between the medulla and the lobula, neuronal fibers reverse their order, inverting the anterior-posterior axis of the visual field (Ito et al., 2014; Shinomiya et al., 2019). Between the medulla and lobula plate and between the lobula and lobula plate, fibers run in parallel, conserving the axes of the visual field (Shinomiya et al., 2019). Neurons travelling between the medulla and lobula complex form around 25-30 fiber bundles of varying widths, and neurons travelling between the same two neuropil columns do not necessarily fasciculate with the same bundle (Shinomiya et al., 2019). Neurons travelling between the lobula and lobula plate form sheet-like structures, neurons from the medulla bundles also merge into these sheets (Shinomiya et al., 2019). Sheets and bundles are wrapped by glial processes (Shinomiya et al., 2019). Approximately 20,000 neurons pass through each second optic chiasma (Shinomiya et al., 2019).

The lobula lies opposite to the lobula plate, with the columns representing the anterior visual field being furthest from the medulla. For that reason, there is no chiasms between the medulla and lobula plate (Ito et al., 2014).