Download Exercise 13

Lab Exercise 13
Histology of Nervous Tissue
Portland Community College
BI 231
Major divisions of the nervous
system
• Central nervous
system (CNS)- brain
and spinal cord
• Peripheral nervous
system (PNS)comprises all nerves
that connect the brain
and spinal cord to
muscles, glands and
receptors.
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Nerves
• Cranial nerves are
those that are
connected to the brain
• Spinal nerves are
connected to the spinal
cord.
• Both contain sensory
information from
receptors and send
motor signals.
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Motor (Efferent) Neurons
Efferent = Away from CNS
• These are neurons that carry information from CNS to
the body
• Groups of axons running together are the Nerves when
they are outside the CNS and Tracts inside the brain
and spinal cord
• The cell bodies are clustered in groups in the CNS and
are called nuclei
• Brain gray matter is made up of millions of nuclei.
• It is gray because there is no myelin around the cell bodies
• These axons exit the spinal cord on the ventral side
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Motor (efferent) division of
PNS
• Somatic nervous
system- contains efferent
neurons extending from
the CNS to skeletal
muscle.
• Autonomic nervous
system- contains
efferent neurons from
CNS to smooth
muscle, cardiac
muscle and glands
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Sensory (Afferent) Neurons
Afferent = Toward the CNS
• These carry sensory information from the body
to the CNS (brain and spinal cord)
• Their axons run in the same group as the motor
neurons (nerves=groups of axons)
• Their cell bodies are clustered outside of the
spinal cord and are called ganglia
• These axons enter the spinal cord on the dorsal
side
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Sensory (afferent) division
• Afferent neurons that
receive stimuli from
somatic sensory receptors
that detect general
sensations
• Receive stimuli from
visceral sensory receptors
• Special sensory receptors
that detect special
sensations (smell, taste,
vision, hearing,
equilibrium)
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Organization of nervous
system
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Neuron
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Myelin
• Some axons are surrounded by a myelin sheath
• Multilayered lipid and protein covering formed
by Schwann cells around axons
• Oligodendrocytes in the CNS
• The covering is the plasma membrane of the
Schwann Cell
• The Schwann Cell can cover more than one axon
• Insulates axon
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Nodes of Ranvier
• Areas between Schwann Cells that do not contain
Myelin
• Involved in saltatory conduction
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Dendrit
e
Nucleu
s
Axon
Hillock
Neuron Cell
Body
Axon
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Schwann
Cell
Axon
Myelin
Sheath
Node of
Ranvier
Telodendria
Axon Terminal (Synaptic end bulbs)
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Classification
• Sensory (afferent)
neurons conduct nerve
impulses from sensory
receptors
• Motor ( efferent)
neurons conduct nerve
impulses from the CNS
• Interneurons form links
between sensory and
motor
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Multipolar Neuron
Cell Body
Axon
Dendrites
(trigger zone)
• Most common type of neuron
• Interneurons and motor neurons
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Anaxonic Neurons
• A small number of
multipolar neurons
contain only dendrites
or
• Cannot distinguish
dendrites from axons
• Functions are poorly
understood.
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Bipolar Neuron
Dendrite
(trigger zone)
Cell Body
Axon
• Location: special senses (smell, vision,
hearing)
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Unipolar Neuron
Dendrite
(trigger zone)
Cell Body
Axon
• All are sensory afferent
• Cell bodies are located in the dorsal root
ganglia
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Association or Interneurons
• Neurons between the afferent and efferent
neurons.
• Are only in the CNS
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Neuron
Axon
Myelin Sheath
Node of Ranvier
Perineurium
Fascicle
Epineurium
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Glial Cells
•
•
•
•
Associated with neurons
Provide Supportive scaffolding
Segregate and insulate neurons
Outnumber neurons by 10 to 1
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Supporting Cells in the CNS
Astrocytes
• Star Shaped
• Many functions
• Regulates levels of O2 ,
• & CO2
•
• Exchanges between capillaries and
neurons (blood-brain barrier)
• Nutrient transfer
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Supporting Cells in the CNS
Microglia
• Protect CNS from
disease-causing
organisms
• Monitor the health of
neurons
• Act as phagocytes
eating microorganisms
and debris
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Ependymal cells
• These cells are
modified epithelial
cells that line the
ventricles of the brain
and central canal of
spinal cord.
• Facilitate circulation
of CSF
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Supporting Cells in the CNS
Oligodendrocytes
• Produce the myelin
sheath which
provides the
electrical insulation
for some neurons in
the CNS
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Supporting Cells in the PNS
Schwann Cells
• Form the myelin sheath around axons in the
PNS
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Satellite cells
• Surround neuron cell
bodies in peripheral
ganglia and regulate
levels of oxygen,
carbon dioxide and
nutrients.
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The synapse
• Axons generate action
potentials which are
transmitted across
synapses
• Formed by presynaptic
membrane and
postsynaptic membrane
on an effector cell
• The synaptic cleft is a
narrow space that
separates these
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The End
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