Lec15 Nervous System

Lec15 Nervous System - Chapter 13 Nervous System Fig. 13.1a...

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Chapter 13 Nervous System
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Fig. 13.1a
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The nervous system Nervous system – Allows for communication between cells through sensory input, integration of data and motor output 2 cell types: neurons and neuroglia
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Expanding on neurons 3 types of neurons: Sensory – takes impulses from sensory receptor to CNS Interneurons – receive information in the CNS and send it to a motor neuron Motor – takes impulses from the CNS to an effector (i.e. gland or muscle fiber) Neuron structure (Ch. 4 review): Cell body – main cell where organelles and nuclei reside Dendrite – many, short extensions that carry impulses to a cell body Axon (nerve fiber) – single, long extension that carries impulses away from the cell body
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12.1 Nervous Tissue cont’ Types of neurons 12-5
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The myelin sheath A lipid covering on long axons that acts to increase the speed of nerve impulse conduction, insulation and regeneration in the PNS Schwann cells – neuroglia that make up the myelin sheath in the PNS Nodes of Ranvier – gaps between myelination on the axons Saltatory conduction – conduction of the nerve impulse from node to node
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12.1 Nervous Tissue cont’ Myelin Sheath: Made up of Schwann cells in PNS (Oligodendrocyte -CNS ) covering found on long axons; insulates; speeds impulse transmission; and has an important role in nerve regeneration within the PNS. 12-6
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Neuron structure
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The nerve impulse: resting potential (RP) Resting potential – when the axon is not conducting a nerve impulse More positive ions outside than inside the membrane There is a negative charge of -65mV inside the axon More Na+ outside than inside More K+ inside than outside Caused by Na+/K+ pump in the membranes
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The nerve impulse: action potential Action potential – rapid change in the axon membrane that allows a nerve impulse to occur Sodium gates open letting Na+ in Depolarization occurs Interior of axon loses negative charge (+40mV) Potassium gates open letting K+ out Repolarization occurs Interior of axon regains negative charge (-65mV) Wave of depolarization/repolarization travels down the axon Resting potential is restored by moving potassium inside and sodium outside
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The nerve impulse: action potential
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Refractory period Period during which nerve conduction is not possible During this period the Na+/K+ pump restores ionic balances to resting value. Helps ensure 1-way conduction of impulses
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The synapse Axons branch into small terminal branches each tipped with an axon bulb Axon bulbs come in very close contact with either the dendrite or cell body of another neuron Region containing the gap between them called a synapse Gap called the synaptic cleft Transmission is accomplished across this gap by a neurotransmitter (e.g. ACh, dopamine and serotonin) small organic compounds that are stored in synaptic vesicles in the pre-synaptic cells Neurotransmitters are stored in synaptic vesicles in the axon terminals
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Lec15 Nervous System - Chapter 13 Nervous System Fig. 13.1a...

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