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Chapter 9

Chapter 9 notes

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Biological Sciences

Chapter 9- The Central Nervous System - in flatworms hard to distinct between central nervous system and peripheral nervous system o there is a cluster of nerve cell bodies concentrated in the head (cephalic) region o 2 large nerves called nerve cords come off the brain and lead to a nerve network which innervates distal regions of the flatworm body o (higher animal) Annelids (earthworms) clusters arent restricted to head, they occur in pairs called ganglia along a nerve cord o Since each segment of the worm contains a ganglion, simple reflexes can be integrated within a segment without input from the brain o Reflexes which dont require integration in the brain also occur in higher animals and are called spinal reflexes in humans and other vertebrates o Annelids and aplysia (shell less mollusk) used for research because their neurons are 10 times larger than in human brain neurons, and have identical number or neurons from animal to animal - brain evolve because they are first to be in contact with the environment - as the brain evolved it became associated with specialized cephalic receptors; eyes for vision and chemoreceptor for smell and taste - in higher arthropods like insects specific regions of brain associated with particular function (complex brain therefore complex behaviour can form colonies, divide labour) - octopus has most sophisticated brain therefore most sophisticated brain development - brain evolution change seen in forebrain region; includes cerebrum o in human brain; cerebrum is what makes the brain; this part allows reasoning and cognition o in birds and rodents; part of the forebrain ahs enlarged into a cerebrum o in fish; small buldge dedicated to processing olfactory information about odours in the environment - change in cerebellum; part of hindbrain o important for coordinating movement and balance o identifiable like cerebrum by grooves and folds Anatomy of the Central Nervous System - in vertebrate nervous system the CNS consists of layers of neural tissue surrounding a fluid filled central cavity which is lined with epithelium - The CNS develops from a hollow tube o In early embryo the cells that become nervous system lie in a flattened region called neural plate o At 20 day of human development neural plate cells along the edge migrate towardrdthe midline o By 23 day the neural plate cells fuse with each other creating neural tube o Neural crest cells from lateral edges of neural plate now lie dorsal to neural tube o Lumen of the neural tube remains hollow and becomes the central cavity of CNS o Cells lining the neural tube will either differentiate into epithelial ependyma or remain undifferentiated neural stem cells www.notesolution.com
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