Transcript 12-02_pptlect
Fundamentals of
Anatomy & Physiology
SIXTH EDITION
Chapter 12, part 2
Neural tissue
PowerPoint ® Lecture Slide Presentation prepared by Dr. Kathleen A. Ireland, Biology Instructor, Seabury Hall, Maui, Hawaii Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
SECTION 12-4 Neurophysiology: Ions and Electrical Signals
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The transmembrane potential
• Electrochemical gradient • Sum of all chemical and electrical forces acting across the cell membrane • Sodium-potassium exchange pump stabilizes resting potential at ~70 mV Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.11 An Introduction to the Resting Potential
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Figure 12.12 Electrochemical Gradients
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Changes in the transmembrane potential
• Membrane contains • Passive (leak) channels that are always open • Active (gated) channels that open and close in response to stimuli Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.13 Gated Channels
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Three types of active channels
• • • Chemically regulated channels Voltage-regulated channels Mechanically regulated channels Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Graded potential
• A change in potential that decreases with distance • Localized depolarization or hyperpolarization Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.14 Graded Potentials
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Figure 12.14 Graded Potentials
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Figure 12.15 Depolarization and Hyperpolarization
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Action Potential
• • Appears when region of excitable membrane depolarizes to threshold Steps involved • Membrane depolarization and sodium channel activation • Sodium channel inactivation • Potassium channel activation • Return to normal permeability Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.16 The Generation of an Action Potential
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Figure 12.16 The Generation of an Action Potential
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Characteristics of action potentials
• • • • Generation of action potential follows all or-none principle Refractory period lasts from time action potential begins until normal resting potential returns Continuous propagation • spread of action potential across entire membrane in series of small steps salutatory propagation • action potential spreads from node to node, skipping internodal membrane Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.17 Propagation of an Action Potential along an Unmyelinated Axon
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Figure 12.18 Saltatory Propagation along a Myelinated Axon
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Figure 12.18 Saltatory Propagation along a Myelinated Axon
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Axon classification
• • • Type A fibers Type B fibers Type C fibers • Based on diameter, myelination and propagation speed Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Muscle action potential versus neural action potential
• • • Muscle tissue has higher resting potential Muscle tissue action potentials are longer lasting Muscle tissue has slower propagation of action potentials
PLAY
Animation: The action potential Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings