1. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Neurons  Neurons = nerve cells  Cells specialized to transmit messages  Major regions of neurons  Cell body  Processes

2. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Neurons  Cell body  Nucleus & large nucleolus, regular organelles except cytoskeleton (*confirms amitotic nature of neurons)  Nissl substance  Specialized rough endoplasmic reticulum  Neurofibrils  Intermediate cytoskeleton  Maintains cell shape

3. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Neurons  Processes outside the cell body  Vary in length from microscopic to 3 – 4 feet  Dendrites—conduct impulses toward the cell body  Axons—conduct impulses away from the cell body  Axon hillock– cone-like region of the cell body  One axon/cell can have many dendrites (and collateral branches)

4. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Neurons (p. 233) Figure 7.4

5. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Processes Cont.  Axon Terminal:  Very branched end of axon;  contain vesicles with neurotransmitters  Axonal terminals are separated from the next neuron by a gap  Synaptic cleft—gap between adjacent neurons  Synapse—junction between nerves

6. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Myelin Sheaths  Whitish, fatty material covering axon  Functions: protection, insulation, & increasing transmission rate of impulses  Schwann cells—produce myelin sheaths in jelly roll–like fashion  Nodes of Ranvier—gaps in myelin sheath along the axon  Multiple Sclerosis (MS) – myelin sheaths gradually destroyed & converted to hardened sheaths called scleroses (scar tissue); autoimmune (protein component is attacked)

7. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Neurons Figure 7.5

8. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Terminology White Matter = dense collections of myelinated fibers (tracts) Gray Matter = unmyelinated fibers & cell bodies CNSPNS Cell bodies in clusters NucleiGanglia Bundles of nerve fibers (neuron processes) TractsNerves

9. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Functional Classification of Neurons  Classified according to the direction the nerve impulse is traveling relative to the CNS  Sensory (afferent) neurons  Carry impulses from the sensory receptors to the CNS  Cutaneous sense organs in skin & Proprioceptors in muscles & tendons

10. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Functional Classification of Neurons Cont’d.  Motor (efferent) neurons  Carry impulses from CNS to viscera, muscles, or glands  Cell bodies are always in the CNS

11. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Functional Classification of Neurons  Interneurons (association neurons)  Found in neural pathways in the CNS  Connect sensory and motor neurons

12. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Functional Classification of Neurons Figure 7.7

13. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Neuron Classification Figure 7.6

14. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Figure 7.8a Structural Classification of Neurons  Based on # of processes extending from cell body  Multipolar neurons—many extensions from the cell body (ex: motor & association neurons)

15. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Structural Classification of Neurons  Bipolar neurons—one axon and one dendrite (rare) Figure 7.8b

16. Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings Structural Classification of Neurons  Unipolar neurons—have a short single process leaving the cell body Figure 7.8c