Human Anatomy

1. © 2012 Pearson Education, Inc.
13
The Nervous System:
Neural Tissue
PowerPoint®
Lecture Presentations prepared by
Steven Bassett
Southeast Community College
Lincoln, Nebraska

2. © 2012 Pearson Education, Inc.
Introduction
• Nervous System Characteristics
• Controls and adjust the activity of the body
• Provides swift but brief responses

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Introduction
• The nervous system includes:
• Central Nervous System (CNS)
• Associated with the brain and the spinal cord
 Integrating, processing, and coordinating
 Intelligence, memory, learning, and emotion
• Peripheral Nervous System (PNS)
• Associated with the tissue outside the CNS
 Neural tissue outside the CNS
 Provides sensory information to the CNS
 Carries motor commands to peripheral tissues

4. © 2012 Pearson Education, Inc.

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An Overview of the Nervous System
• The Peripheral Nervous System (PNS) can be
subdivided into:
• Afferent: Brings sensory information toward the CNS
• Receptors, which transform different stimuli into Action
Potential, belong to this division.
• Which can be further subdivided into somatic and visceral
• Efferent: Carries motor commands away from the
CNS
• Effectors, that respond to the CNS commands, belong
to this division.
• Which can be further subdivided into somatic nerves and
autonomic nerves

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Figure 13.1 The Nervous System
CENTRAL NERVOUS
SYSTEM
Brain
Spinal cord
Peripheral nerves
PERIPHERAL NERVOUS
SYSTEM

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An Overview of the Nervous System
• The Peripheral Nervous System (PNS)
• Afferent
• Sensory portion: monitors skeletal muscles and
joints
• Visceral portion: monitors smooth muscles,
cardiac muscle, and other internal organs
• Efferent
• Somatic nerves: controls skeletal muscle
contraction
• Autonomic nerves: controls internal organ
activities

8. © 2012 Pearson Education, Inc.
Afferent division
The afferent division carries information from
 Somatic sensory receptors
 Skeletal muscles, joints, and the skin
 Visceral sensory receptors
 Smooth muscle, cardiac muscle, and glands
 Special sense organs
 Eye, nose, tongue, and ear

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Efferent division
The efferent division begins inside the CNS and ends at an effector.
 The efferent division
 Somatic nervous system (SNS)
 Skeletal muscle contractions
 May be voluntary or involuntary
 Autonomic nervous system (ANS)
 Visceral motor system
 Smooth muscle, cardiac muscle, and glands
 Involuntary
 Includes sympathetic and parasympathetic divisions.

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Figure 13.2 A Functional Overview of the Nervous System
CENTRAL NERVOUS SYSTEM
(brain and spinal cord)
PERIPHERAL
NERVOUS
SYSTEM
RECEPTORS EFFECTORS
Information
processing
Sensory
information
within
afferent
division
Motor
commands
within
efferent
division
Includes
Somatic nervous
system
Autonomic
nervous system
Parasympathetic
division
Sympathetic
division
Skeletal
muscle • Smooth
muscle
• Cardiac
muscle
• Glands
Special sensory
receptors (provide
sensations of smell,
taste, vision,
balance, and
hearing)
Somatic sensory
receptors (monitor
skeletal muscles, joints,
skin surface; provide
position sense and
touch, pressure, pain,
and temperature
sensations)
Visceral sensory receptors (monitor
internal organs, including those
of cardiovascular, respiratory, digestive,
urinary, and reproductive systems)

11. © 2012 Pearson Education, Inc.
Cellular Organization in Neural Tissue
• Neural tissue consists of two cell types:
• Neurons
• Nerve cells that are responsible for the transfer
and processing of information in the nervous
system
• Consist of a soma, axon, and dendrites
• Neuroglia
• Supporting cells
• Protect the neuron

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Figure 3.23a Histology of Neural Tissue
Brain
Spinal cord
Cell body
Axon
Nucleus of
neuron
Nucleolus
Dendrites
Diagrammatic view of a representative neuron

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Cellular Organization in Neural Tissue
• Functions of Neuroglia
• Provide the framework for the neural tissue
• Maintain the intercellular environment
• Act as phagocytes
• Over 100 billion
• Roughly five times the number of neurons
• Also called glial cells
• Have the ability to reproduce

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Cellular Organization in Neural Tissue
• Neuroglia Cells
• Neuroglia cells of the CNS
• Astrocytes
• Oligodendrocytes
• Microglia
• Ependymal cells
• Neuroglia cells of the PNS
• Satellite cells
• Schwann cells

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Figure 13.4 The Classification of Neuroglia
Neuroglia
Peripheral Nervous System Central Nervous System
are found in
containscontains
Satellite cells Schwann cells Oligodendrocytes Astrocytes Microglia Ependymal cells
Surround neuron cell
bodies in ganglia;
regulate O2, CO2,
nutrient, and
neurotransmitter levels
around neurons in
ganglia
Surround all axons in
PNS; responsible for
myelination of
peripheral axons;
participate in repair
process after injury
Myelinate CNS
axons; provide
structural
framework
Maintain blood–brain
barrier; provide structural
support; regulate ion,
nutrient, and dissolved-gas
concentrations; absorb and
recycle neurotransmitters;
form scar tissue after injury
Remove cell
debris, wastes,
and pathogens
by phagocytosis
Line ventricles
(brain) and central
canal (spinal cord);
assist in producing,
circulating, and
monitoring
cerebrospinal fluid

16. © 2012 Pearson Education, Inc.
Cellular Organization in Neural Tissue
• Neuroglia of the CNS
• Astrocytes
• Largest and most numerous glial cells
• Have a large number of cytoplasmic processes
• Control the chemical content of the interstitial
environment
• Maintain the blood–brain barrier
• Isolate the neurons from general circulation
 Creating a three-dimensional framework for the CNS
 Performing repairs in damaged neural tissue
 Guiding neuron development

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Cellular Organization in Neural Tissue
• Neuroglia of the CNS
• Oligodendrocytes
• Cytoplasmic extensions contact the somas or
axons
• Cytoplasmic extensions tie axons together in a
sheath of myelin
• Microglia
• Phagocytic cells
• Protect the neuron by removing waste and debris

18. © 2012 Pearson Education, Inc.
Cellular Organization in Neural Tissue
• Neuroglia of the CNS
• Ependymal cells
• Line the ventricles of the brain
• Line the central canal of the spinal cord
• Monitor the CSF (cerebrospinal fluid)
composition
• Some ependymal cells secrete CSF

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Figure 13.5 Histology of Neural Tissue in the CNS
Gray
matter
White
matter
Internode
Neurons
Myelinated
axons
Myelin
(cut)
Axon Axolemma
Oligodendrocyte
Myelin sheath
gap
Unmyelinated
axon
Basal lamina
Capillary
Astrocyte
Microglial
cell
Ependymal
cells
CENTRAL CANAL

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Figure 13.6a The Ependyma
Light micrograph showing the
ependymal lining of the central canal
POSTERIOR
ANTERIOR
LM × 450
Gray matter
White matter
Central canal
Ependymal
cells
Central
canal
Central canal

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Cellular Organization in Neural Tissue
• Neuroglia of the PNS
• Satellite cells
• Regulate the exchange of material between the
cell body and the environment
• Schwann cells
• Also called neurolemmocytes
• Form a myelin sheath

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Figure 13.7 Satellite Cells and Peripheral Neurons
Nerve cell body
Nucleus
Satellite cells
Connective
tissue
Peripheral ganglion LM × 25

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Figure 13.8a Schwann Cells and Peripheral Axons
Axon hillock
Axon
Nucleus
Dendrite
Myelinated
internode Initial
segment
(unmyelinated)
Myelin sheath gaps
Schwann
cell nucleus
Axon
neurolemma
neurolemma
Myelin
covering
internode
Axon
Axolemma
Axons
Myelin
TEM × 20,600Myelin sheath
A single Schwann cell forms the myelin sheath
around a portion of a single axon. This situation
differs from the way myelin forms inside the CNS.
Compare with Figure 13.5.

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Figure 13.8b Schwann Cells and Peripheral Axons
neurolemma
neurolemma
Schwann
cell nucleus
Schwann
cell
Axons
Myelin
sheath
gap
Schwann
cell nucleus
Axons
Axons
TEM × 27,625Unmyelinated axons
A single Schwann cell can encircle several
unmyelinated axons. Unlike the situation inside
the CNS, every axon in the PNS has a complete
neurolemmal sheath.

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Cellular Organization in Neural Tissue
• Neuron Structure
• Cell body
• Nucleus
• ER
• Ribosomes (Nissl bodies)
• Neurofilament
• Cell extensions
• Dendrite
• Axone
• Initial segment: the very beginning of the axon
• Axon terminal: the very end of the axon
• Axon collateral: the side branches of axon.
• Axolemma: the outermost covering of an unmyelinated axon.
• Nodes: areas of myelinated axon that are not covered by myelin.

26. © 2012 Pearson Education, Inc.
Figure 13.3 A Review of Neuron Structure
Dendrites Cell body Axon Terminal boutons
Stimulated by
environmental changes or
the activities of other cells
Contains the nucleus,
mitochondria, ribosomes, and
other organelles and inclusions
Conducts nerve impulse
(action potential) toward
synaptic terminals
Affect another neuron
or effector organ
(muscle or gland)
Axon hillock
Mitochondrion
Nucleus
Nucleolus
Nissl bodies
(clusters of RER
and free ribosomes)
Dendritic
spines

27. © 2012 Pearson Education, Inc.
Figure 13.9 Anatomy of a Representative Neuron
A neuron may innervate (1) other neurons, (2) skeletal muscle
fibers, or (3) gland cells. Synapses are shown in boxes for each
example. A single neuron would not innervate all three.
Multipolar neuron
1. Synapses with another neuron
2. Neuromuscular synapses
3. Neuroglandular synapses
Neuroglandular
synapses
Gland
cells
Skeletal
muscle
Neuromuscular
synapses
Terminal boutons
Terminal arborization
Collateral
branch
Synapses with
another neuron
Neuron
Dendrites Axolemma
Neuron
Nerve cell body LM × 1600
Dendrite
Nucleus
Nucleolus
Dendritic
spines
Chromatophilic
substance
Neurofilament
Nerve cell body
Mitochondrion
Golgi apparatus
Axon hillock
Initial segment
of axon
Nerve cell body
Nucleolus
Nucleus
Axon hillock
Initial segment
of axon
Chromatophilic
substance
Neurofilament
Terminal
boutons
Postsynaptic
cell
Axon (may be
myelinated)

28. © 2012 Pearson Education, Inc.
Figure 13.10 A Structural Classification of Neurons
Anaxonic neuron Bipolar neuron Pseudounipolar neuron Multipolar neuron
Dendrites
Dendrite
Axon
Axon
Axon
Axon
Dendrites Dendrites
Initial
segment
Terminal
boutons
Terminal
boutons
Terminal
boutons
Anaxonic neurons
have more than two
processes, but
axons cannot be
distinguished from
dendrites.
Bipolar neurons
have two processes
separated by the
cell body.
Pseudounipolar
neurons have a single
elongate process with
the cell body situated
to one side.
Multipolar neurons
have more than two
processes; there is a
single axon and
multiple dendrites.

29. © 2012 Pearson Education, Inc.
Cellular Organization in Neural Tissue
• Functional Classification of Neurons
• Sensory
• Sends information from the PNS to the CNS
• Somatic sensory and visceral sensory
• Motor
• Sends information from the CNS to the periphery
• Interneurons
• Situated between the motor and sensory neurons
• Analyze sensory input and coordinate motor
outputs
• Can be excitatory or inhibitory

30. © 2012 Pearson Education, Inc.
Figure 13.2 A Functional Overview of the Nervous System
CENTRAL NERVOUS SYSTEM
(brain and spinal cord)
PERIPHERAL
NERVOUS
SYSTEM
RECEPTORS EFFECTORS
Information
processing
Sensory
information
within
afferent
division
Motor
commands
within
efferent
division
Includes
Somatic nervous
system
Autonomic
nervous system
Parasympathetic
division
Sympathetic
division
Skeletal
muscle • Smooth
muscle
• Cardiac
muscle
• Glands
Special sensory
receptors (provide
sensations of smell,
taste, vision,
balance, and
hearing)
Somatic sensory
receptors (monitor
skeletal muscles, joints,
skin surface; provide
position sense and
touch, pressure, pain,
and temperature
sensations)
Visceral sensory receptors (monitor
internal organs, including those
of cardiovascular, respiratory, digestive,
urinary, and reproductive systems)

31. © 2012 Pearson Education, Inc.
Cellular Organization in Neural Tissue
Receptors are monitored by the sensory neurons
 Exteroceptors = external environment
 Touch, temperature, and pressure sensations
 Special senses of sight, smell, and hearing
 Proprioceptors = internal environment
 Position and movement of skeletal muscles and joints
 Information carried in somatic sensory neurons
 Interoceptors = internal environment
 Digestive, respiratory, cardiovascular, urinary, and
reproductive systems
 Sensations of deep pressure and pain as well as taste

32. © 2012 Pearson Education, Inc.
Figure 13.11 A Functional Classification of Neurons
RECEPTORS PERIPHERAL NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM
EFFECTORS
Interoceptors
Exteroceptors
Proprioceptors
Skeletal muscles
Skeletal
muscle
fibers
Visceral effectors
Smooth
muscles
Glands
Cardiac
muscle
Adipose
tissue
Afferent fibers
Efferent fibers
Postganglionic
fibers
Preganglionic
fibers
Sensory neurons
in peripheral
ganglia
Visceral
motor neurons
in peripheral
motor ganglia
Somatic
motor
neurons
Visceral
motor
neurons
in CNS
Interneurons
= Somatic (sensory & motor)
= Visceral (sensory & motor)

33. © 2012 Pearson Education, Inc.
The Nerve Impulse
Excitability is the ability of a plasmalemma to
conduct electrical impulses.
An electrical impulse, or action potential, develops
after the plasmalemma is stimulated to its threshold.
Nerve impulse is an action potential traveling along
an axon.
The rate of impulse conduction depends on the
properties of the axon, specifically:
 Presence or absence of myelin sheath
 The diameter

34. © 2012 Pearson Education, Inc.
Figure 13.9b Anatomy of a Representative Neuron
A neuron may innervate (1) other neurons, (2) skeletal muscle
fibers, or (3) gland cells. Synapses are shown in boxes for each
example. A single neuron would not innervate all three.
1. Synapses with another neuron
2. Neuromuscular synapses
3. Neuroglandular synapses
Neuroglandular
synapses
Gland
cells
Skeletal
muscle
Neuromuscular
synapses
Terminal boutons
Terminal arborization
Collateral
branch
Synapses with
another neuron
Neuron
Dendrites Axolemma
Neuron

35. © 2012 Pearson Education, Inc.
Figure 13.13a The Structure of a Synapse
Diagrammatic view of a vesicular synapse between two neurons
Terminal boutons
Terminal arborization
Postsynaptic neurons
Myelin
Axon
Dendrites
Synapse
Terminal
arborization
Impulse
conduction
Endoplasmic
reticulum
Terminal bouton
Mitochondrion
Synaptic vesicles
Presynaptic membrane
Synaptic cleft
Postsynaptic membrane

36. © 2012 Pearson Education, Inc.
Figure 13.14 Organization of Neuronal Circuits
Divergence Convergence Serial processing Parallel processing Reverberation
Divergence, a mechanism
for spreading stimulation
to multiple neurons or
neuronal pools in the CNS
Convergence, a
mechanism providing
input to a single
neuron from multiple
sources
Serial processing,
in which neurons
or pools work in a
sequential manner
Parallel processing, in
which individual neurons
or neuronal pools
process information
simultaneously
Reverberation, a
feedback
mechanism that
may be excitatory or
inhibitory

37. © 2012 Pearson Education, Inc.
Figure 13.15 Anatomical Organization of the Nervous System
PERIPHERAL NERVOUS SYSTEM
RECEPTORS
CENTRAL NERVOUS SYSTEM
EFFECTORS
PATHWAYS
GRAY MATTER
WHITE MATTER
WHITE MATTER ORGANIZATION
GRAY MATTER ORGANIZATION
Neural Cortex
Nuclei
Tracts
Centers
Higher Centers
Columns
Ganglia
Nerves
Collections of
neuron cell bodies
in the PNS
Bundles of axons
in the PNS
Centers and tracts that connect
the brain with other organs and
systems in the body
Ascending (sensory) pathway
Descending (motor) pathway
Bundles of CNS
axons that share a
common origin and
destination
Several tracts that
form an anatomically
distinct mass
Collections of
neuron cell bodies
in the interior of
the CNS
The most complex
centers in the brain
Gray matter on the
surface of the brain
Collections of
neuron cell bodies
in the CNS; each
center has specific
processing functions