In Man,
Neural Networks consist of two or more neurons with highly specialized non-neural sensory receptor cells, that are responsive to very specific environmental stimuli such as light, heat, osmolarity, stretching, pressure, or pain.   Sensory neurons lead from receptor cells to other neurons;  Motor neurons lead to muscle cells;  and Interneurons connect Sensory and Motor neurons to each other.

      The diagram above displays the interconnections of neurons that form simple Neural Networks.   The Afferent Axons of sensory neurons excite four interneurons, A, B, D, and E.   Of these, B and D send impulses out of the system as Efferent Axons to excite other systems.   Closed loops are formed by A-B-B', and B-C-C'.