Fundamentals of the Nervous
System and Neural Tissue
Part A
Human Anatomy & Physiology, Sixth Edition
Elaine N. Marieb
11
Nervous System
Figure 11.1
Divisions of the Nervous System
Divisions of the Nervous System
CNS
PNS
Efferent
(motor)
neurons
Sympathetic
ANS
Parasympathetic
Somatic
Afferent
(sensory)
neurons
Neuroglia – Supporting Cells
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Provide scaffolding for neurons
Segregate & insulate neurons
Guide growing neurons to proper connections
Promote health & growth of neurons
Cell types
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Astrocytes
Microglial cells
Ependymal cells
Oligodentrocytes
Schwann cells
Satellite cells
Astrocytes
 Abundant, versatile, and highly branched CNS cell
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Cover capillaries
Support & brace neurons
Anchor neurons to their nutrient supplies
Guide migration of young neurons
Control the chemical environment
Microglial Cells
 Microglia – small, ovoid cells with spiny processes
 Phagocytic
 Monitor health of neurons
Ependymal Cells
 Squamous or columnar cells lining ventricles of brain
and spinal cord
Oligodendrocytes
 Branched cells that wrap CNS nerve fibers (axons)
Schwann Cells and Satellite Cells
 Schwann cells surround axons of PNS neurons
 Satellite cells surround bipolar neuron cell bodies
in ganglia
Myelin Sheath and Neurilemma Formation
 Whitish, fatty (protein-lipid), segmented sheath around
most long axons sphingomyelin
 Formed by:
 Schwann cells in the PNS
 Oligodendrocytes in CNS
 Functions to:
 Protect axons
 Electrically insulate fibers
 Increases speed of impulse transmission
Myelin Sheath and Neurilemma Formation
 A Schwann cell:
 Encloses the axon with its
plasma membrane
 Concentric layers of
membrane make up the
myelin sheath
 Neurilemma
 Nucleus and cytoplasm of a
Schwann cell
Neurons (Nerve Cells)
 Functional units of neurons
 Composed of a body, axon, and
dendrites
 Long-lived, amitotic, and have a high
metabolic rate
 Plasma membrane functions in:
 Electrical signaling
 Cell-to-cell signaling during
development
Axon Function
 Generate and transmit action potentials
 Secrete neurotransmitters from termini
 Intracellular movement along axons
 Anterograde — toward terminus
 Retrograde — away from terminus, toward soma
Axons of the CNS
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Both myelinated and unmyelinated fibers are present
Myelin sheaths are formed by oligodendrocytes
Nodes of Ranvier are widely spaced
There is no neurilemma
Regions of the Brain and Spinal Cord
 White matter – dense collections of myelinated fibers
 Gray matter – mostly soma and unmyelinated fibers
Neuron Classification
 Structural:
 Multipolar - three or more processes
 Bipolar - two processes (axon and dendrite)
 Unipolar - single process diverges into 2 conductive
regions
 Functional:
 Sensory (afferent) — transmit impulses toward the CNS
 Motor (efferent) — carry impulses away from the CNS
 Interneurons (association neurons) — shuttle signals
through CNS pathways
Structural Classes of Neurons
Structural Classes of Neurons
Structural Classes of Neurons