The Nervous System:
Neural Tissue
Chapter 13
Introduction
• Nervous system =
control center &
communications
network
• Functions
– Stimulates
movements
– Maintains
homeostasis
(with endocrine
system)
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Organization of the Nervous System
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Functional Classification of the
Peripheral Nervous System
• Sensory (afferent)
division
• Nerve fibers that
carry information to
the central nervous
system
• Motor (efferent)
• Nerve fibers that
carry information
from the central
nervous system
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Histology of Nervous Tissue
• 2 types of cells
– Neurons
• Structural & functional part of nervous system
• Specialized functions
– Neuroglia (glial cells)
• Gli = glue
• Support & protection of nervous system
Neuroglia
• Neuroglia of CNS
–
–
–
–
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
Neuroglia of CNS
• Astrocytes
• Form the bloodbrain barrier
• Structural
framework for CNS
• Repair damaged
neural tissue
• Control the
interstitial
environment of
the brain
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neuroglia of CNS
• Oligodendrocytes
• Produce myelin
sheath around
nerve fibers in the
central nervous
system
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neuroglia of CNS
• Microglia
• Spider-like
phagocytes
• Dispose of debris
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neuroglia of CNS
• Ependymal cells
• Line ventricles of the brain and spinal cord
• Secrete cerebrospinal fluid
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neuroglia of CNS
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neuroglia of PNS
• Schwann cells
– Form myelin sheaths of PNS
• Satellite cells
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neurons
• Function
– Conduct
electrical
impulses
• Structure
– Cell body
• Nucleus with
nucleolus
• Cytoplasm
(perikaryon)
– Cytoplasmic
processes
• Dendrites
• Axon
Human Anatomy, 3rd edition
Prentice Hall, © 2001
• Long, specialized
Axon Structure
– Collaterals = branches
– Telodendria = termination of axons & collaterals
• Cytoplasm = axoplasm
• Plasma membrane = axolemma
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Anatomy of a Neuron
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Nerve Fibers of the PNS
• An axon and its sheaths
– Myelinated axon
• Axon is surrounded by a myelin sheath
– Unmyelinated axon
• Axon has no myelin sheath
Myelin
• White matter of
nerves, brain, spinal
cord
• Composed primarily
of phospholipids
• Production
– Developing Schwann
cells wind around
axon
• Neurilemma
– Peripheral
cytoplasmic layer of
the Schwann cell
enclosing the myelin
Human Anatomy, 3rd edition
sheath
Prentice Hall, © 2001
A Myelinated Axon
• Function of myelin
– Increases speed of
impulse conduction
– Insulation and
maintenance of axon
• Nodes of Ranvier
– Unmyelinated gaps
between segments of
myelin
– Impulses “jump”
from node to node
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Nerve Fibers of the CNS
• Unmyelinated
• Myelinated
– Production of
myelin is from
oligodendrocytes
– Nodes of Ranvier
are less numerous
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Structural Classification of Neurons
• Based on the number of cytoplasmic processes
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Functional Classification of Neurons
• Based on the direction of impulse transmission
– Sensory neurons
– Motor neurons
– Interneurons (association)
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Nerve Impulse
• A change in charge that travels as a wave
along the membrane of a neuron
• Called an action potential
• Depends on the movement of sodium ions
(Na+) and potassium ions (K+) between the
interstitial fluid and the inside of the
neuron.
Resting Potential
• Sodium ions are in large concentration along the
outside of the cell membrane
• Potassium ions are in large concentration along the
inside of the cell membrane
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Beginning of a Nerve Impulse
• Requires a stimulus of adequate strength
• Membrane is irritable
– Neuron may respond to a stimulus and convert
it to an impulse.
• When?
– If above threshold
Starting a Nerve Impulse
• Depolarization – a
stimulus depolarizes
the neuron’s
membrane
• A depolarized
membrane allows
sodium (Na+) to flow
inside the membrane
• The exchange of ions
initiates an action
potential in the neuron
Human Anatomy, 3rd edition
Prentice Hall, © 2001
The Action Potential
• If the action
potential starts, it is
propogated over
the entire axon
• Potassium ions
rush out of the
neuron after
sodium ions rush in
– Repolarizes the
membrane
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%
20102/Bio%20102%20lectures/nervous%20system/neuron6.gif
Return to Resting Potential
• Sodium-potassium
pump restores original
configuration
– Requires ATP
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio
%20102/Bio%20102%20lectures/nervous%20system/neuron6.gif
Nerve Impulse Propagation
• The impulse continues
to move away from
the cell body
• Impulses travel faster
when fibers have a
myelin sheath
Continuation of the Nerve Impulse
Between Neurons
• Impulses are able to cross a synapse to another nerve
– Neurotransmitter
is released from
the axon terminal
(synaptic knob)
into synaptic cleft
– The dendrite of the
next neuron has
receptors that are
stimulated by the
neurotransmitter
Synaptic Cleft
Postsynaptic Membrane Receptor
Synapse
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neural Regeneration After Injury
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neural Regeneration
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neural Regeneration
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neural Regeneration
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Nerves
• Neurons are bundled
into fasciculi which
are bundled into
nerves.
– Endoneurium
surrounds each nerve
fiber (axon)
– Groups of fibers are
bound into fascicles
• Surrounded by the
perineurium
– Fascicles are bound
together into a nerve
• Surrounded by
the epineurium