The Functional Organization within the Ommatidium of the Lateral Eye of Limulus

Abstract

This chapter discusses the distinguishing characteristics of the electrical activity recorded with intracellular microelectrodes from retinular and eccentric cells in the lateral eye of Limulus polyphemus . The retinular cell is the primary photoreceptor; the eccentric cell is not inherently photosensitive and is, therefore, the second-order neuron in the visual pathway. Adjacent retinular cells are connected by a doubly rectifying electrotonic tight junction, whereas the individual retinular cells are joined to eccentric cells via a singly rectifying electrotonic tight junction. The effect of the generator potential on the spike generator can be modulated via the lateral inhibition that the eccentric cell of one ommatidium exerts on eccentric cells of neighboring ommatidia. A model of the organization of a single ommatidium in the form of an equivalent electrical circuit is presented in the chapter; this model can simulate both the manner where the cells behave to applied currents and the interactions among ommatidial cells.