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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
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
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)
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons (p. 233)
Figure 7.4
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
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)
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Nervous Tissue: Neurons
Figure 7.5
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Terminology
White Matter = dense collections of myelinated fibers (tracts)
Gray Matter = unmyelinated fibers & cell bodies
CNS PNS
Cell bodies in clusters
Nuclei Ganglia
Bundles of nerve fibers
(neuron processes)
Tracts Nerves
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
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
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
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Functional Classification of Neurons
Figure 7.7
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Neuron Classification
Figure 7.6
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)
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings
Structural Classification of Neurons Bipolar neurons—one axon and one dendrite (rare)
Figure 7.8b
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