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BIOL 373: Chapter 9 Textbook Notes

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BIOL 373
Heidi Engelhardt

Evolution of Nervous Systems st Jellyfishsea anemones Cnidarians 1 multicellular animals to develop neurons o Nervous system nerve net composed of sensory neurons connective interneurons and motor neurons that innervate muscles and glands o Respond to stimuli but without input from a control centreNOTE action potentialselectrochemical signals are the same in all animals It is only the number and organization of the neurons that one species differs from another Flatworms contain a rudimentary brain consisting of a cluster of nerve cell bodies concentrated in the head region o No distinction between CNS and PNS o 2 large nerve cords extend from primitive brain and innervates distal regions of the bodySegmented wormsannelids earthworms clusters of cell bodies ganglia occur in fused pairs along a nerve cord not just in the head like in flatworms o Due to ganglia in each segment simple reflexes can occur without input from the brain spinal reflexesNOTE one advantage to cephalic brains brains in the head region is that in most animals the head is the part of the body that first contacts the environment as the animal moves o As brain evolved it became associated with specialized receptors for vision smell tasteInsects arthropods specific regions of the brain are associated with particular functionsMore complex brainsmore complex behaviours octopus most complex invertebrateVertebrate evolution most dramatic change in the forebrain region which includes the cerebrum o Fish forebrain is a small bulge mainly for processing olfactory information o Birdsrodents part of the forebrain has enlarged into a smooth cerebrum o Humans cerebrum is the largest part of the brain with deep groovesfolds o Cerebellum region of hindbrain coordinates movement and balanceDevelopment of the Vertebrate CNS lumen becomes the central cavity of the CNS Neural plateneural tubeneural tube cells differentiate into ependyma or remain neural stem cells outer neural tube cells become neurons and glia of the CN 1
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