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1 Ent 207 Lecture 9/10 January, 2007. NERVOUS SYSTEM Divide into three major parts: A. Central nervous system B. Visceral nervous system C. Peripheral nervous system Parts B. and C. are not discussed here. Basic element of the nervous system is the nerve cell (neuron). - consists of: see Sketch cell body - contains nucleus and most organelles. cytoplasmic extensions. one extension (usually shorter) = dendrite - receives information. second extension = axon - carries information to other cells. (with sensillum = sensory neuron.) - both dendrites and axons can branch - increases integration of inputs and outputs. - most synapses occur in aggregations of neurons (neuropile of ganglion). - nerve = bundle of axons. 2 Central Nervous System 1. major portions ventrally located. 2. segmentally arranged. 3. segments with a pair of ganglia: concentration of neurons which act as integration centres. 4. all connectives are paired (reflection of annelid-like ancestor?) - connectives lack cell bodies. - groups of axons - variable size. 5. fusion of ganglia - variable among insect species and stage. - in primitive insects, many pairs of ganglia (reflection of segmental architecture). in "advanced " insects. Anterior: cephalization - brain (lies above esophagus). Posterior - ganglia and connectives located ventrally. - terminal ganglion often quite large - "posterior brain" . 6. cephalization - condensation of nervous system towards anterior end produces two large ganglion: - cerebral ganglion = brain. - subesophageal ganglion. - numerous coordinating/integrating functions. - fusion of multiple segmental ganglia. - sensory information from and control of head appendages: mouthparts, antennae, eyes - some axons pass directly from brain to other parts (pass through ganglia) and others pass from parts of body to brain. - reduced number 3 Brain And Subesophageal Ganglion sketch protocerebrum - most complex optic lobe (part of protocerebrum)-largest part serves compound eye (adults) - a lot of visual integration. - ocellar centres - ocelli. (vision and light perception) - location of centres which controls most complex behaviour. deutocerebrum - olfactory lobes - antennal nerve - (sense of smell). very large - receive and process information that helps the insect: i. find food. ii. locate oviposition sites. iii. find mates. iv. sense danger - ants, bees. - all mediated by volatile chemicals in the environment. - for mate finding use species-specific volatile chemical signals known as pheromones. (other senses are involved in mate-finding). tritocerebrum - receives input from the labrum, possibly parts of head capsule. (taste and mechanoreception). - connects with ventral chain of ganglia. - connects (via other ganglia and nerves not described here to several pairs of endocrine glands that help regulate moulting and suboesophageal ganglion- fusion of three ganglia. (mandibular, maxillary, labial). - nerves from these three sets of mouthparts. - taste and mechanoreception. Sensing the Environment How is this done with a cuticular covering? metamorphosis).