This arrangement is suited for direct transmission of environmental stimuli to the central nervous system. Information from outside of an insect, such as light or mechanical stimulus, is most likely conducted from peripheral sense cells directly to central nervous system ganglia by axons without synaptic interruptions. These axons are called afferent axons. Most afferent neurons synapse with other neurons that in turn synapse with still other neurons or else with efferent neurons. The neurons that form connections between afferent and efferent neurons are called interneurones.
Nerve fibers are generally aggregates of several or many neurons.
The central nervous system is not centrally located Unlike vertebrates, in which a single, relatively large brain is encased in a skull, central nervous systems of insects are composed of variously distributed ganglia. The major association center is called the brain. The other important ganglia are subesophageal ganglion, frontal ganglion, up to three thoracic ganglia and up to eight abdominal ganglia. The deutocerebrum contains antennal lobes, from which project both afferent and efferent neurons. The tritocerebrum is a small, bilobed ganglion.