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PowerPoint® Lecture Slides
prepared by Leslie Hendon,
University of Alabama,
Birmingham
12
HUMAN
ANATOMY
fifth edition
MARIEB | MALLATT | WILHELM
PART 2
Fundamentals
of the
Nervous
System and
Nervous
Tissue
Copyright © 2008 Pearson Education, Inc.,
publishing as Benjamin Cummings
Classification of Neurons

Structural classification
 Multipolar – possess more than two processes
 Numerous dendrites and one axon
 Bipolar – possess two processes
 Rare neurons
 Found in some special sensory organs
 Unipolar (pseudounipolar) – possess one short,
single process
 Start as bipolar neurons during development
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Neurons Classified by Structure
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.10a
Neurons Classified by Structure
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.10b
Neurons Classified by Structure
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.10c
Functional Classification of Neurons

Functional classification is
 According to the direction the nerve impulse
travels

Sensory (afferent) neurons
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Functional Classification of Neurons

Transmit impulses toward the CNS
 Virtually all are unipolar neurons
 Cell bodies in ganglia outside the CNS
 Short, single process divides into
 The central process – runs centrally into the
CNS
 The peripheral process – extends
peripherally to the receptors
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Functional Classification of Neurons

Motor (efferent) neurons
 Carry impulses away from the CNS to effector
organs
 Most motor neurons are multipolar
 Cell bodies are within the CNS
 Form junctions with effector cells

Interneurons (association neurons) – most are
multipolar
 Lie between motor and sensory neurons
 Confined to the CNS
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Neurons Classified by Function
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.11
Supporting Cells

Six types of supporting cells
 Four in the CNS
 Two in the PNS


Provide supportive functions for neurons
Cover nonsynaptic regions of the neurons
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Neuroglial in the CNS

Neuroglia
 Glial cells have branching processes and a central
cell body
 Outnumber neurons 10 to 1
 Make up half the mass of the brain
 Can divide throughout life
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Neuroglia in the CNS

Astrocytes are the most abundant glial cell type
 Sense when neurons release glutamate
 Extract blood sugar from capillaries for energy
 Take up and release ions in order to control
environment around neurons
 Involved in synapse formation in developing neural
tissue
 Produce molecules necessary for neuronal growth
(BDTF)
 Propagate calcium signals involved with memory
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Neuroglia in the CNS
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.12a
Neuroglia in the CNS

Microglia –
smallest and least
abundant glial cell
 Phagocytes – the
macrophages
of the CNS
 Engulf invading
microorganisms
and dead neurons
 Derive from blood
cells called
monocytes
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.12b
Neuroglia in the CNS

Ependymal cells
 Line the central cavity of the spinal cord and brain
 Bear cilia – help circulate the cerebrospinal fluid

Oligodendrocytes – have few branches
 Wrap their cell processes around axons in CNS
 Produce myelin sheaths
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Neuroglia in the CNS
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.12c, d
Neuroglia in the PNS


Satellite cells – surround neuron cell bodies
within ganglia
Schwann cells (neurolemmocytes) – surround
axons in the PNS
 Form myelin sheath around axons of the PNS
Copyright © 2008 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12.13