A molecule released by a cell or a gland in one part of the body that sends out messages affecting cells in other parts of the organism.
The nervous system has three overlapping functions based on the sensory input, integration, and motor output. The nervous system is a highly integrated system.
Sensory input comes from the many sensory receptors that monitor changes occurring both inside and outside the body. The total sum of the information gathered by these receptors is called sensory input. The nervous system processes and interprets sensory input and decides what actions should be taken. The nervous system activates effectororgans such as muscles and glands to cause a response called motor output.
At a more integrative level, the primary function of the nervous system is to control and communicate information throughout the body. It does this by extracting information from the environment using sensory receptors. This sensory input is sent to the central nervous system, which determines an appropriate response.
Once the response is activated, the nervous system sends signals via motor output to muscles or glands to initiate the response.
In humans, the sophistication of the nervous system allows for language, abstract representation of concepts, transmission of culture, and many other features of society that would not otherwise exist.