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Unformatted text preview: Chapter 48: Nervous Systems 48.1 Nervous systems consist of circuits of neurons and supporting cells- All animals except sponges have some type of nervous system Organization of Nervous Systems- Cnidarians: simplest animals w/nervous systems- Radially symmetrical bodies organized around a gastrovascular cavity- Hydra: neurons controlling contraction & expansion of gastrovascular cavity are arranged in diffuse nerve nets- Nerves = bundles of fiberlike extensions of neurons - i.e. sea stars have a nerve net in each arm- connected by radial nerves to a central nerve ring- better suited than a diffuse nerve net for controlling more complex movements- cephalization: clustering of neurons in a brain near anterior end in animals w/ elongated, bilaterally symmetrical bodies- central nervous system (simple)- small brain & longitudinal nerve cords - annelids, arthropods- more complicated brains & ventral nerve cords- ganglia = segmentally arranged clusters of neurons - peripheral nervous system = nerves that connect CNS w/ rest of animal’s body- nervous system organization correlates w/ an animal’s lifestyle- sessile/slow moving mollusks (i.e. clams & chitons)- have little or no cephalization- relatively simple sense organs- cephalopod mollusks (i.e. squids & octopuses)- most sophisticated systems of any invertebrates- large brain- large, image-forming eyes- rapid signaling along nerves- supports active, predatory life Information Processing- 3 stages in processing info by nervous systems A. sensory input B. integration C. motor input- stages are handled by specialized populations of neurons- sensory neurons = transmit info from sensors that detect external stimuli (light, sound, touch, heat, smell, & taste) and internal conditions (blood pressure, blood CO 2 )- information is sent to CNS- interneurons integrate (analyze & interpret) the sensory input- taking into account:- immediate context - what happened in past- greatest complexity exists in connects between interneurons- motor output leaves CNS via motor neurons- communicate w/ effector cells = muscle cells / endocrine cells- stages are easiest to study in reflexes- body’s automatic responses to stimuli Neuron Structure- Cell body = contains most of neuron’s organelles & nucleus- Dendrites = highly branched extensions that receive signals from other neurons- Axon = much longer extension that transmits signals to other cells (neurons/effector cells)- Axon hillock = conical region of an axon where it joins the cell body- region where signals that travel down axon are generated- myelin sheath = layer that encloses an axon- near its end, axon divides into several branches, each ends in a synaptic terminal- synapse = site of communication btwn a synaptic terminal & another cell- presynaptic cell = the transmitting cell- postsynaptic cell = receiving cell- neurotransmitters = chemical messengers that that transmit information Supporting Cells (Glia)- Glia = supporting cells essential for structural integrity of nervous system & normal functioning of...
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This note was uploaded on 04/17/2009 for the course BISC 220 taught by Professor Mcclure during the Spring '09 term at USC.
- Spring '09