The nervous system brings about integration and co-ordination of several activities of the animal. The afferent stimuli from several sense organs are brought to the brain, which is the coordinating centre. From the brain suitable efferent stimuli are transmitted to various motor or effector organs resultant in coordinated motor activities of the animal. You have seen that these stimuli travel by a closed system of circuits comparable to telegraphic cables, called nerve fibres, in the form of electrical disturbances. There are indeed many minute gaps among the connections where neurotransmitters make and break the circuits between gaps. There is another equally important system, which also serves transmission of messages form one part of the body to another, bringing about integration and coordination of various activities of the animal. This is the endocrine system. The endocrine system brings about communication by chemical substances called hormones produced by endocrine glands. The hormones are transported to their target tissues or organs through the blood stream. The nervous system and the endocrine system make an integral part of the coordinating system of the animal. In fact the two systems are closely related with each other and the branch of study of the two closely- knit interacting systems are termed as neuroendocrinology.