Transcript Central nervous system

The Nervous System: Neural
Tissue
Chapter 9a
Introduction
– Nervous system = control center &
communications network
– Functions
• Stimulates movements
• Maintains homeostasis (with endocrine
system)
Organization of the Nervous System
– Central nervous system
(CNS)
• Brain & spinal cord
– Peripheral Nervous
System (PNS)
• Afferent (Sensory)
System
• Efferent (Motor)
System
– Somatic Nervous
System
– Autonomic Nervous
System
» Sympathetic
Nervous System
» Parasympathetic
Human Anatomy, 3rd edition
Nervous System Prentice Hall, © 2001
Organization of the 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
Neurons
– Function
• Conduct electrical
impulses
– Structure
• Cell body
– Nucleus with
nucleolus
– Cytoplasm
• Cytoplasmic
processes
– Dendrites
– Axon
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
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Myelin
– White matter of nerves,
brain, spinal cord
– Composed primarily of
phospholipids
– Production
• Developing Schwann cells
wind around axon
– Function
• Increases speed of impulse
conduction
• Insulation and maintenance
of axon
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Myelin
– 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
– Umyelinated
– Myelinated
• Production of myelin
is from
oligodendrocytes
• Nodes of Ranvier are
less numerous
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Classification of Neurons
– Functional – based on the
direction of impulse
transmission
• Sensory neurons
• Motor neurons
• Interneurons
(association)
Functional Classification of Neurons
Human Anatomy, 3rd edition
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Nerve Impulse
– A change in charge that travels as a wave along
the membrane of a neuron
– Depends on the movement of K+ and Na+
across the nerve cell membrane.
– Called an action potential
Resting Neuron
– 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
– Membrane is polarized
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 = a critical level
– Minimum stimulus required to elicit a response
Starting a Nerve Impulse
• Depolarization – a
stimulus begins the change
in charge on 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
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The Action Potential
• If the action potential (nerve
impulse) starts, it is
propagated over the entire
axon
• Potassium ions rush out of
the neuron after sodium ions
rush in
• Sodium and potassium are
actively transported back to
their original positions =
repolarization
• Membrane is at rest again
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Nerve Impulse Propagation
• The impulse continues to
move away from the cell
body
• Impulses travel faster when
fibers have a myelin sheath
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Continuation of the Nerve Impulse between
Neurons
• Impulses are able to cross the synapse to another
nerve
• Neurotransmitter is released from a nerve’s axon
terminal
• The dendrite of the next neuron has receptors that are
stimulated by the neurotransmitter
How Neurons Communicate at Synapses
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Synapses
Human Anatomy, 3rd edition
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Neural Regeneration
Human Anatomy, 3rd edition
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Neural Regeneration
Human Anatomy, 3rd edition
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Neural Regeneration
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neural Regeneration
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Structure of a Nerve
• Endoneurium surrounds
each fiber
• Groups of fibers are bound
into fascicles by the
perineurium
• Fascicles are bound
together by epineurium
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Classification of Nerves
• Mixed nerves
• Both sensory and motor fibers
• Afferent (sensory) nerves
• Carry impulses toward the CNS
• Efferent (motor) nerves
• Carry impulses away from the CNS