1. ELAINE N. MARIEB EIGHTH EDITION 7 Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings PowerPoint ® Lecture Slide Presentation by Jerry L. Cook, Sam Houston University ESSENTIALS OF HUMAN ANATOMY & PHYSIOLOGY PART A The Nervous System

2. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Neurons  Neurons = nerve cells….NOT NERVES!  transmit messages  Major regions of neurons  Cell body – nucleus and metabolism  Processes – fibers extending from the cell body

3. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Anatomy  Cell body  Processes of cell body  Dendrites – conduct impulses toward the cell body (incoming)  Axons – conduct impulses away from the cell body (outgoing) Figure 7.4a–b

4. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Axons and Nerve Impulses  Axons end in axonal terminals  Axonal terminals contain vesicles with neurotransmitters  Axonal terminals are separated from the next neuron by a gap (synaptic cleft)  *Synapse – junction between nerves

5. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings How Neurons Communicate at Synapses Figure 7.10

6. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nerve Fiber Coverings  Schwann cells – produce myelin sheaths in jelly-roll like fashion  Nodes of Ranvier – gaps in myelin sheath along the axon Figure 7.5

7. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Component Location  Gray matter – cell bodies and unmyelinated fibers  Areas where signals are processed  Cortex of brain  Center of spinal cord  White matter – myelinated axons  Areas where signals are transmitted  Center of brain  Outer area of spinal cord

8. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functional Classification of Neurons  Sensory neurons  Carry impulses from the sensory receptors to CNS  Motor neurons  Carry impulses from CNS  Interneurons  Connect sensory and motor neurons in the CNS

9. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Classification Figure 7.6

10. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 7.3a Nervous Tissue: Support Cells (Neuroglia)  Astrocytes  Abundant, star-shaped cells  Brace neurons  Form barrier between capillaries and neurons  Control the chemical environment of the brain

11. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Support Cells  Microglia  Spider-like phagocytes  Dispose of debris  Ependymal cells  Line cavities of the brain and spinal cord  Circulate cerebrospinal fluid Figure 7.3b–c

12. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Support Cells  Oligodendrocytes  Produce myelin sheath around nerve fibers in the central nervous system Figure 7.3d

13. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Figure 7.3e Nervous Tissue: Support Cells  Satellite cells  Protect neuron cell bodies  Schwann cells  Form myelin sheath in the peripheral nervous system

14. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Functional Properties of Neurons  Irritability – ability to respond to stimuli  Conductivity – ability to transmit an impulse  The plasma membrane at rest is polarized  Fewer positive ions are inside the cell than outside the cell

15. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Starting a Nerve Impulse  Depolarization – a stimulus depolarizes the neuron’s membrane  A depoloarized membrane allows sodium (Na + ) to flow inside the membrane  The exchange of ions initiates an action potential in the neuron Figure 7.9a–c

16. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Nerve Impulse Propagation  The impulse continues to move toward the cell body  Impulses travel faster when fibers have a myelin sheath Figure 7.9d–f

17. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings The Action Potential  If the action potential (nerve impulse) starts, it continues over the entire axon  Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane  The sodium-potassium pump restores the original configuration  This action requires ATP

18. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Continuation of the Nerve Impulse between Neurons  Impulses can cross the synapse to another nerve  Neurotransmitter is released from the axon terminal  Dendrite on next neuron has receptors that are stimulated by the neurotransmitter  An action potential is started in the dendrite

19. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings How Neurons Communicate at Synapses Figure 7.10