The Nervous System
The Nervous System
 The
master
controlling and
communication
system of
the body
Three Overlapping Functions
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Sensory Input
Monitors internal and external stimuli (Changes)
 Afferent pathway to the brain
 receptors
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Integration
Processes and interprets information
 Decides the appropriate response
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Motor Output
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Efferent pathway to effector organs (muscles or
glands), effects a response
Organization of the Nervous System
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Central Nervous System (CNS)
Brain and spinal cord
 Dorsal body cavity
 Integrating command center
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Peripheral Nervous System (PNS)
Nerves to and from brain and spinal cord
 Communication links to the CNS
 Spinal nerves and cranial nerves
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Peripheral Nervous System
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Sensory Afferent Division
Impulses to the brain and spinal cord (CNS)
 Monitors internal and external changes
 Somatic afferent
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Skin, skeletal muscle, joints
Visceral afferent
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Organs within ventral body cavity
Peripheral Nervous System
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Motor Efferent Division
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From CNS to effector muscle, organs, and glands
Somatic efferent nervous system
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Voluntary nervous system
Autonomic nervous system
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Involuntary
Visceral motor nerve fibers (to smooth and cardiac muscle and
glands)
Sympathetic (emergency situations)
Parasympathetic (conserves energy, nonemergency functions)
Classification

P. 224
Nervous System
THE CELLS OF THE NERVOUS
SYSTEM
Nervous Tissue-Types of Cells
Two Principal Cell Types Neurons: excitable nerve cells
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Supporting cells: Neuroglia “Nerve Glue”
 Support, insulate, and protect neurons by surrounding and
wrapping neurons.
 Central nervous system supporting cells
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Astrocytes
Microglia
Ependymal cells
Oligodendrocytes
Peripheral nervous system supporting cells
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Satellite cells
Schwann cells
Neuroglia-Supporting
Cells of CNS
Astrocytes
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Most abundant *Star-shaped
Radiating processes cover neurons and anchor them to
adjacent blood vessels
Controls exchange between blood vessels and neurons
Determines capillary permeability
Astrocytes (Cont)
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Controls chemical environment around neurons
Cleans up leaked potassium and recycling released
neurotransmitter
Guide migration of young neurons
Microglia
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Small, ovoid cells, with thorny processes (spider-like)
Branches monitor health of neurons
Migrate toward injured neuron
Transform into a macrophage when invading microorganisms
or dead neurons are present and dispose of debris
Protective role because cells of immune system are denied
access to CNS
Ependymal cells
Simple squamous to columnar in shape
 Line the cavities of the brain and spinal cord
 Beating of their cilia circulates cerebrospinal fluid
that cushions brain and spinal cord
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Oligodendrocytes
Wrap cytoplasmic extensions around neurons and
form myelin sheaths in CNS
 Insulates and protects
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Supporting Cells of the PNS
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Satellite cells
 Surround neuron cell bodies within ganglia
 Protective and cushioning cells
Schwann cells
 Surround and form myelin sheaths around larger nerve
fibers
 Functionally similar to oligodendrocytes
Neurons
Highly specialized to transmit nerve
impulses
Neurons
Nerve cells
Structural units of the nervous system
Special characteristics of neurons:
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1.
2.
3.
4.
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Conduct nerve impulses
Extreme longevity
Amiotic (exceptions: olfactory and hippocampus) (become
injured and do not regenerate)
High metabolic rate: requires abundant oxygen and glucose
All Neurons have cell bodies and processes, plus
three functional components: receptive or input
region, conducting component, and secretory or
output component.
Cell Body
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Metabolic center
No centrioles
Ribosomes and rough ER (Nissl Substance)most active
of any cell in the body
Plasma membrane acts as part of the receptive surface
Most located within the CNS (called nuclei)
Cell body collections in the PNS are called ganglia
Cell Processes
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Brain and spinal cord (CNS) contain both cell bodies
and their processes
The PNS consists chiefly of neuron processes
Bundles of neuron processes are called tracts (CNS)
and nerves (PNS).
Dendrites
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Short, tapering, hundreds/cell
Receptive (input) region; convey incoming messages(electrical
signals) toward the cell body
Large surface area
Cell Processes
Axon (conducting component)
One Axon (Single process) per neuron
 Axon arises from axon hillock of cell body
 Generates nerve impulses and transmits them away from
the cell body
 Long axons called nerve fibers
Axon terminals –created where the axon branches at the
terminal end
 100-1000+ terminal branches per axon
 Axon terminals are the secretory portion—secretes
neurotransmitters

Myelin Sheath (neurilemma)
Myelin: whitish, fatty material covering long nerve
fibers; has waxy appearance
 Protects and provides an electrical insulation
covering for large and long nerve fibers
 Increases speed of transmission of nerve impulses
 Unmyelinated fibers conduct impulses slowly
 Associated only with axons; Dendrites always
unmyelinated
 Formed by Schwann cells in PNS—made of
concentric layers of cell membranes (no channel or
carrier proteins) called the neurilemma
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Myelin (Cont)
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Nodes of Ranvier are the gaps between Schwann cells—
regularly spaced
Oligodendrocytes form CNS myelin sheaths—coils around
60 fibers at the same time—no neurilemma because of the
absence of coiling of cells
Regions of the brain and spinal cord with myelinated fibers
called white matter.
Gray matter contains mostly cell bodies and unmyelinated
fibers
Classification of Neurons
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Structural Classification
Multipolar neurons
 Bipolar neurons
 Unipolar Neurons
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Functional Classification
Sensory (afferent) neurons
 Motor (efferent) neurons
 Association (interneurons) neurons
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Nervous Tissue Structures
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p. 227
CELL
BODY
DENDRITE
Nervous Tissue Structures
AXON
AXON
TERMINAL
Nervous Tissue Structures
SCHWANN
CELLS
NODES OF
RANVIER