Download Chapter 7 Notes Part 2

Nervous Tissue: Neurons
 Neurons = nerve cells
 Cells specialized to transmit messages
 Major regions of neurons
 Cell body
 Processes
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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
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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)
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Nervous Tissue: Neurons (p. 233)
Figure 7.4
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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
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Terminology
CNS
PNS
Cell bodies in
clusters
Nuclei
Ganglia
Bundles of
nerve fibers
(neuron
processes)
Tracts
Nerves
White Matter = dense collections of myelinated
fibers (tracts)
Gray Matter = unmyelinated fibers & cell bodies
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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
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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
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Neuron Classification
Figure 7.6
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Structural Classification of Neurons
 Based on # of processes extending from cell body
 Multipolar neurons—many extensions from the
cell body (ex: motor & association neurons)
Figure 7.8a
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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
Copyright © 2009 Pearson Education, Inc., publishing as Benjamin Cummings