Nervous System and Sense Organs
The non-chordates also perform a variety of activities such as feeding, digestion, locomotion etc. For this aim, they have corresponding organs and organ systems working in a coordinated way. Furthermore, the environment of the animal, both internal and external, is never stable and the animal has to change its activities in relation to the changing environmental conditions. This involves escape from adverse climatic conditions or from a pursuing predator, catch food to overcome hunger, digests the food for energy needs, excrete waste material, and regulate the respiratory rate and so on. Towards this purpose, the concerned organs must be coordinated in an efficient and purposeful manner. This is brought about mostly by the nervous system.
Essentially, the animal has to perceive any change in the environment, compute the changes and finally translate these computations into requisite actions in a manner most profitable and adaptive to the animal. In the direction of this goal the nervous system has receptor components consisting of sense organs, coordinating centers in the central nervous system and the motor components controlling the motor elements. The system is connected all through so to say, by cables of nerves through which messages or impulses flow as if on a telegraphic system. The receptor organs receive messages from the environment that are transmitted to the central nervous system. The central nervous system is the decision centre that sends requisite orders to the effector organs through motor neurons.