Synaptic organization of the lobster optic lamina

Abstract

The most superficial neuropile region of the optic lobe, the optic lantina, or lamina ganglionaris, of arthropods is placed between the retina and the second neuropile layer, the medulla. The retina in the crustacean compound eye is built up of a large number of ommatidia, which are the characteristic light-perceptive cells, each consisting of 6-8 retinula cells in most species. The retinula cell membrane is elaborated into a complex light-sensitive system of tubules called the rhabdomere by which the energy of the photon is transformed to nervous excitation, not necessarily impulses. The optic lamina is the place where the retinula cell axons, after passing through the basement membrane in small bundles, terminate upon the axons of ganglion cells of the lamina. After a decussation in the optic chiasma, the second-order fibers reach the medulla, where they terminate on the third neuron in the chain (Fig. I). In other words, the optic lamina is the first of a series of relay stations on the optic pathway. Since the functional properties of the retinula cells can be recorded directly with microelectrodes in favorable species, an elucidation of the morphology of the first synapse will assist in the interpretation of the function of the lamina. Show more