Chapter 48 Nervous System

Biology, 7th Edition (Book & CD-ROM)

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Chapter 48 Nervous System I. Circuits of Neurons A. Organization of Nervous Systems 1. Hierarchy a. Sponges i No nervous system b. Cnidarians (hydra) i Have nerve nets c. Echinoderm (sea star) i Has a nerve ring in the middle with a radial nerve protruding out to each arm 2. CNS and PNS a. CNS- has the brain and longitudinal nerve cords (spine) b. PNS- has ganglia. Which are nerves that connect the CNS with the rest of the animal’s body B. Information Processing Reflex- body’s automatic response to stimuli 1. Sensory neurons- transmit information from sensors that detect external stimuli and internal conditions. It goes from stimulus CNS via sensory neurons 2. Interneurons- analyze and interpret the sensory input 3. Motor neurons- send information from CNS to effector cells (muscle/gland) C. Neuron Structure 1. Cell body a. Most of a neuron’s organelles and its nucleus are located here 2. Dendrites a. Very many of them b. Receive signals from other neurons 3. Axon a. Much longer extension b. Transmits signals to other cells (neurons or effectors) c. Greatly varies in length 4. Axon Hillock a. A conical region of an axon where it joins the cell body 5. Myelin sheath a. A layer which covers each axon 6. Synaptic terminal a. The axon divides into several branches, and each branch ends in a synaptic terminal 7. Synapse a. The site of communication between a synaptic terminal and another cell b. Information is passed via neurotransmitters D. Supporting Cells (glia) 1. Astrocytes 1
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a. Provide structural support b. Regulate the extracellular concentrations of ions and neurotransmitters c. Facilitate the transformation of information at the neuron’s synapses sometimes d. Make tight junctions between cells during development i Causes a blood brain barrier, which doesn’t let many substances into the CNS 2. Oligodendrocytes a. Form the myelin sheaths around the axons of vertebrate neurons in the CNS 3. Schwann Cells a. Form the myelin sheaths around the axons of vertebrate neurons in the PNS 4. Myelin sheath a. Membrane by itself is a poor conductor of electrical currents. Myelin sheath provides electrical insulation of the axon. II. Ion Pumps and Channels A. Resting Potential 1. Resting potential- normally between -60 and -80 when the cell is not transmitting signals 2. Depends on the gradients of ions a. The K + and Na + ion gradients are regulated by the sodium-potassium pump B. Gated Ion Channels 1. Ungated channels- ion channels that are always open a. Used for potassium and sodium 2. Gated ion channels- open or close in response to stimuli 3. Types of Stimuli a. Stretch-gated ion channels- found on cells that sense stretch and open when membrane is deformed b. Ligand-gated ion channels- found at synapses and open or close when a neurotransmitter binds to the channel c. Voltage-gated ion channels- open or close when the membrane potential changes III. Action Potentials A. Definitions 1. Hyperpolarization- an increase in the magnitude of the membrane potential
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Chapter 48 Nervous System - Chapter 48 Nervous System I....

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