tailieunhanh - Entomology 3rd edition - C.Gillott - Chapter 13

13 Nervous and Chemical Integration 1. Introduction Animals constantly monitor both their internal and their external environment and make the necessary adjustments in order to maintain themselves optimally and thus to develop and reproduce at the maximum rate. | 13 Nervous and Chemical Integration 1. Introduction Animals constantly monitor both their internal and their external environment and make the necessary adjustments in order to maintain themselves optimally and thus to develop and reproduce at the maximum rate. The adjustments they make may be immediate and obvious for example flight from predators or longer-term for example entry into diapause to avoid impending adverse conditions. The nature of the response depends obviously on the nature of the stimulus. Only very rarely does a stimulus act directly on the effector system almost always a stimulus is received by an appropriate sensory structure and taken to the central nervous system which determines an appropriate response under the circumstances. When a response is immediate that is achieved in a matter of seconds or less it is the nervous system that transfers the message to the effector system. Such responses are usually temporary in nature. Delayed responses are achieved through the use of chemical messages viz. hormones and are generally longer-lasting. The nervous and endocrine systems of an individual are then the systems that coordinate the response with the stimulus. Semio-chemicals which constitute another chemical regulating system coordinate behavior and development among individuals. They comprise pheromones intraspecific coordinators and allelochemicals interspecific coordinators which include kairomones and allomones. 2. Nervous System Like that of other animals the nervous system of insects consists of nerve cells neurons and glial cells. Each neuron comprises a cell body perikaryon where a nucleus many mitochondria and other organelles are located and a cytoplasmic extension the axon which is usually much branched the branches being known as neurites. Axons may be long as in sensory neurons motor neurons and principal interneurons or very short as in local interneurons. Often insect neurons are monopolar lacking the dendritic tree characteristic