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Fundamentals of the
Nervous System and
Nervous Tissue
Functions of the Nervous
System
1. Sensory input
2. Integration
3. Motor output
Sensory input
Integration
Motor output
Figure 11.1
Divisions of the Nervous System
• Central nervous system (CNS)
• Peripheral nervous system (PNS)
Peripheral Nervous System (PNS)
•
Two functional divisions
1. Sensory (afferent) division
• Somatic afferent fibers
•
Visceral afferent fibers
2. Motor (efferent) division
• Somatic efferent fibers
•
Visceral efferent fibers
Visceral Motor Division of PNS
Autonomic nervous system (ANS)
– Two functional subdivisions
• Sympathetic
• Parasympathetic
Histology of Nervous Tissue
•
Two principal cell types
1. Neurons –
2. Neuroglia (glial cells)
– Astrocytes (CNS)
– Microglia (CNS)
– Ependymal cells (CNS)
– Oligodendrocytes (CNS)
– Satellite cells (PNS)
– Schwann cells (PNS)
Astrocytes
Neuron
Astrocyte
Astrocytes are the most abundant
CNS neuroglia.
Microglia
Neuron
Microglial
cell
Microglial cells are defensive cells in
the CNS.
Ependymal Cells
Fluid-filled cavity
Ependymal cells line cerebrospinal
fluid-filled cavities.
Ependymal
cells
Brain or
spinal cord
tissue
Oligodendrocytes
Myelin sheath
Process of
oligodendrocyte
Nerve
fibers
Oligodendrocytes have processes that form
myelin sheaths around CNS nerve fibers.
Satellite Cells and Schwann Cells
• Satellite cells
• Schwann cells
Satellite
cells
Cell body of neuron
Schwann cells
(forming myelin sheath)
Neurons (Nerve Cells)
• Structure
– Dendrite
– Axon
– Soma
Dendrites
(receptive regions)
Cell body
(biosynthetic center
and receptive region)
Nucleolus
Axon
(impulse generating
and conducting region)
Nucleus
Nissl bodies
Axon hillock
(b)
Impulse
direction
Node of Ranvier
Schwann cell
Neurilemma (one interTerminal
node)
branches
Axon
terminals
(secretory
region)
Figure 11.4b
Properties of Neurons
• Excitability
• Conductivity
• Secretion
Neuron Classification
Figure 7.6
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.15
Functional Classification of Neurons
•
Three types:
1. Sensory (afferent)
2. Motor (efferent)
3. Interneurons (association neurons)
Myelin Sheath
• Produced by oligodendrocytes in CNS
• Produced by Schwann cells in PNS
• Internodes
• Nodes of Ranvier
The Action Potential
 If the action potential (nerve impulse)
starts, it is propagated over the entire
axon
 Potassium ions rush out of the neuron
after sodium ions rush in, which
repolarizes the membrane
 The sodium-potassium pump restores
the original configuration
 This action requires ATP
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.19
The Synapse
• A junction that mediates information transfer
from one neuron
• Presynaptic neuron
• Postsynaptic neuron
Electrical Synapses
• Less common than chemical synapses
• Neurons are joined by gap junctions
• Communication is very rapid, and may be
unidirectional or bidirectional
• Always excitatory
Chemical Synapses
• Specialized for the release and reception
of neurotransmitters
• Slower than electrical synapses
• Can be excitatory or inhibitory
• Typically composed of two parts
– Axon terminal of the presynaptic neuron,
which contains synaptic vesicles
– Receptor region on the postsynaptic
neuron
Neural Integration: Neuronal Pools
• Functional groups of neurons that:
– Integrate incoming information
– Forward the processed information to
other destinations
Types of Circuits in Neuronal Pools
• Diverging circuit
– One incoming fiber stimulates an everincreasing number of fibers, often
amplifying circuits
– May affect a single pathway or several
– Common in both sensory and motor
systems
Figure 11.22a
Types of Circuits in Neuronal Pools
• Converging circuit
– Opposite of diverging circuits, resulting
in either strong stimulation or inhibition
– Also common in sensory and motor
systems
Figure 11.22c, d
Types of Circuits in Neuronal Pools
• Reverberating (oscillating) circuit
– Chain of neurons containing collateral
synapses with previous neurons in the chain
Figure 11.22e
Types of Circuits in Neuronal Pools
• Parallel after-discharge circuit
– Incoming fiber stimulates several neurons in
parallel arrays to stimulate a common output
cell
Figure 11.22f