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.
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). - reduced number 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.
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 metamorphosis).
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?