Copyright 2009 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Neurons Neurons = nerve cells Cells specialized to transmit

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


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


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)


Nervous Tissue: Neurons (p. 233)

Figure 7.4


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


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)


Nervous Tissue: Neurons

Figure 7.5


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


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


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


Functional Classification of Neurons Interneurons (association neurons)

Found in neural pathways in the CNS Connect sensory and motor neurons


Functional Classification of Neurons

Figure 7.7


Neuron Classification

Figure 7.6


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)


Structural Classification of Neurons Bipolar neurons—one axon and one dendrite (rare)

Figure 7.8b


Structural Classification of Neurons Unipolar neurons—have a short single process

leaving the cell body

Figure 7.8c

Documents

Copyright 2009 Pearson Education, Inc., publishing as Benjamin Cummings Nervous Tissue: Neurons Neurons = nerve cells Cells specialized to transmit