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Structure of the Nervous System and Evolution .docx

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Natural Science
Course Code
NATS 1675
Ruthanna Dyer

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th September 15 lecture Systems – chpt 8, 5, 6 Structure of the Nervous System & Evolution Invertebrates: coelenterates: (sea anenamie, bottom of sea with lots of tentacles, in sea water) - Animals with 2 body layers (no middle) inside & outside – do not have N.S - In the wall of coelenterate consists of outside & inside, is a single layer of cells with a space in b/w (2 layers not touching each other) which is filled with ECF – Mesoglea. - The animals nerve cells are located in the mesoglea (look in notebook for figures) - In most coelenterates have cell body with nucleus in it - Nerves form a net – if looking at organisms in a flat view, interconnected nerve cells form a network of cells in either the inside/outside layer of animal. - Two types of nerve nets: one associated with each of the 2 layers in the animal’s body. These nerve nets cannot connect/talk to each other except for 1 place: around the animals mouth  hole in the middle where all the tentacles surround/meet together. Around the mouth: ring of nerve cells where outside & inside rings are joined together - Simple animals do have nervous systems but they are rudimentary: mostly made up of a single type of nerve cell- connected together to form nerve nets - Nerve cord on ventral side of animal Segmentally Arranged Animals (worms, crabs) = made up of segments - Tend to get an aggregation of nerve cells in each body segment called the ganglion - Segemental ganglia are connected longitudinally by a nerve cord - [Side note: in vertebrates, nerve cord (spinal cord) on dorsal side of the animal] - Each segmental ganglia= give rise to segmental nerves, which supply segmental muscles (or segmental anything) located in that segment – local control of segments by segmental nerves, however it is integration of local segmental events by means of longitudinal ventral nerve chord which communicates adjacent segments with one another from the length of the animal (how worm movements) - As animals get more complicating, segments started to fuse together, as this happened, the segmental ganglia also fused together therefore fewer ganglia which got bigger - Tendency as animals got more complicating – for progressive fusion of segmental ganglia together - Figure in textbook: in the abdomen of the animal, these are segmental ganglia, but towards the front of the animal= more extensive fusion of the ganglia, produce much bigger ganglia (formation of brain – evolution causing animal complexity to increase, particularily at the front end) - Why the front end? Enormous importance for animals to know whats in front of you  sensory organs built to determine this (ex: eyes, nose) so b/c what is in front of us is so important, it parallels with more complex system of nerve cells/systems in front of us - Some invertebrates have an entirely second nervous system devoted to the control of non-segmental structures – the heart, the gut, the reproductive system – things not segmentally repeated. Stromatogastric Nervous System: stomach, mouth, gut- analogous to autonomic N.S in mammals (parasympathetic and sympathetic) - Which way does info travel in nervous system? Information goes up and down from segments – head - Segmental nerves are bidirectional – outputs that control the muscles in segments and inputs that control the
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