The Endocine System, the Nervous System, and Behavior The nervous system is usually thought of as the mediator of behavior, but the endocrine system is also a major player. Arguing that one system is more important would be like deciding whether height, width, or depth is more important in describing a box. It is useful, however, to discuss their differences. The nervous system has a shorter response time. Nerve impulses travel at speeds of up to 120 meters per second. Hormonal effects are much slower but are less transitory. If frightened by a false alarm, an animal may jump and run as a direct consequence of nervous system activity, but even after it recognizes that there is no real threat, it will be "keyed-up." This is a consequence of hormonal activity: Fright triggered the release of epinephrine (adrenaline) and norepinephrine from the adrenal glands. These hormones cause increased cardiac output; increased blood supply to the brain, heart, and muscles; decreased blood flow to the digestive tract; dilation of airways to breath more efficiently; and a significant increase in metabolic rate. This is called the "fight or flight reaction," and it will affect behavior for several minutes and possibly for hours. These hormones enhance perceptions and elevate the responsiveness of the nervous system. In the final analysis, the understanding of hormones, what determines their ebb and flow, how they are affected by the environment, how hormones interact with one another, and how their levels are controlled by genetic programs of the individual and of the species is essential for the understanding of behavior.
Talking to Animals Animal communication provides a fascinating frontier for exploration. Some of the knowledge acquired has had practical applications as well. Pheromones have been used to bait traps for insect pests. In some cases, this technique is used directly as a control measure; in other instances, the traps are used to estimate population size, and other control measures are used when pest populations are high. A key advantage of pheromone use is its specificity. Recognizing the communication signals of pets and domestic animals is often useful in their care. Knowledge of releasers, standard signals that receive standard responses from animals, is important for survival in some contexts. Knowing which signals are perceived by animals as threats allows humans to avoid triggering an attack. This knowledge also allows control of animals in less destructive ways. Recordings of alarm signals of birds are used to disperse flocks that are creating problems. Knowledge of a species' communication repertoire is critical in the training of animals for useful work or for entertainment. Also, knowledge of their sensory capacities makes it possible for appropriate signals to be selected-particularly important as it applies to human nonverbal communication. Knowing which signals of our nonverbal communication repertoire are characteristic of the whole species is both useful and interesting.
