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Chapter 10
Nervous System
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Divisions of the Nervous System
• Central nervous system (CNS)
– Consists of brain and
spinal cord
• Peripheral nervous system
(PNS)
– Consists of nerve network
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Central and Peripheral Nervous
Systems
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Neuroglia
• Supportive cells of the nervous system
– Oligodendrocytes: Form myelin sheath in
the CNS
– Ependymal cells: Line spinal cord and cavities
of the brain
– Microglia: Perform phagocytosis
– Astrocytes: Form blood–brain barrier
– Schwann cells: Form myelin sheath in
peripheral nervous system
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Blood–Brain Barrier
• Formed as astrocytes wrap
around capillaries
• Protects brain from
foreign substances
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Neurons
• Handle communication
• Three classes
– Sensory (afferent) neurons: Detect stimuli
– Interneurons: Connect pathways
– Motor (efferent) neurons: Relay messages
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Neuron Structure
Cell body
Dendrites
Axon
Myelin sheath
Nodes of Ranvier
Synaptic knob
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Myelin Sheath
Peripheral nervous
system
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Central nervous
system
Impulse Conduction
• Caused by an electrical current
• Membrane potential: When ions with
opposite electrical charges are separated
by a membrane
• Polarization: When a membrane has an
excess of positive ions on one side and
an excess of negative ions on the other
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Impulse Conduction: Step 1
Resting Potential
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Impulse Conduction: Step 2
Depolarization
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Impulse Conduction: Step 3
Action Potential
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Impulse Conduction: Step 4
Repolarization
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Impulse Conduction: Step 5
Refractory Period
View animation on “nerve impulse conduction in unmyelinated fibers”
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Impulse Conduction:
Myelinated Fibers
1.
2.
View animation on “Impulse in myelinated fibers”
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Synapses
View animation on “Synapses”
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