The Nervous System
 Structural Divisions
 Functional Divisions
 Neural Tissue
Structural Divisions
 Central Nervous System (CNS) – consists of the brain and
spinal cord
 Peripheral Nervous System (PNS) – consists of all nerves
and ganglia that lie outside the CNS
Central Nervous System (CNS)
 The central nervous system includes the brain and spinal
cord. The brain and spinal cord are complex organs,
composed of neural tissue, blood vessels and various
connective tissues.
 The CNS is responsible for integrating, processing, and
coordinating sensory information (internal and external
conditions) and motor commands (control or adjust
activities of the PNS).
Peripheral Nervous System (PNS)
 Consists of cranial nerves that arise from the brain and
spinal nerves that emerge from the spinal cord.
 Sensory, or afferent, neurons are nerve cells delivers
information to the CNS.
 Motor, or efferent, neurons originate within the CNS and
send information out to the muscles and glands.
 The PNS can be divided into two subgroups: the Somatic
Nervous System and the Autonomic Nervous System.
The Somatic Nervous System
 SNS consists of sensory neurons that convey information
from sense receptors to the CNS and motor neurons from
the CNS that conduct impulses to skeletal muscles.
 The SNS is voluntary because these motor responses can be
consciously controlled.
The Autonomic Nervous System
 The ANS consists of sensory neurons that convey
information from receptors to the CNS and motor neurons
from the CNS that conduct impulses to smooth muscle,
cardiac muscle, and glands.
 The ANS is unvoluntary because these motor responses are
not consciously controlled.
 The motor portion of the ANS consists of two branches: the
Sympathetic Division and the Parasympathetic Division.
The Sympathetic and Parasympathetic Divisions of the ANS
 The viscera, with few exceptions, receive instructions from
both.
 The two divisions typically have opposite actions. Processes
promoted by the sympathetic neurons use energy, while
processes promoted by the parasympathetic neurons
restore/conserve energy.
Nervous Tissue
 Neurons
 Neroglia
Neuroglia
 About half the space in the CNS is filled by neuroglia
(“glue”).
 Neuroglia isolate neurons, provide supporting framework
for neural tissue, act as phagocytes, and help regulate
composition of interstitial fluid.
 There are four types of neuroglia in the CNS: Astrocytes,
Oligodendrocytes, Microglia, and Ependymal Cells.
Astrocytes
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“star cell”
Star shaped cells.
Participate in metabolism of neurotransmitters.
Maintain the proper balance of K+ for generation of nerve
impulses.
 Participate in brain development.
 Help form the blood-brain barrier, which regulates the
entry of substances into the brain.
 Provide a link between neurons and blood vessels.
Oligodendrocytes
 “few tree”
 Smaller than astrocytes.
 Form a supporting network by wrapping around neurons
and producing a lipid and protein covering called a myelin
sheath.
Microglia
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“small glue”
Small, phagocytic neuroglia.
Derived from monocytes.
Protect the CNS from disease by engulfing invading
microbes and clearing away debris from dead cells.
Ependymal cells