The Nervous System: Neural
Tissue
Chapter 9a
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
–
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
Nervous System
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Organization of the Nervous System
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
Human Anatomy, 3rd edition
Prentice Hall, © 2001
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
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
http://www.britannica.com/EBchecked/topic-art/409665/66781/Conduction-of-the-action-potential-In-a-myelinated-axon-the
Human Anatomy, 3rd edition
Prentice Hall, © 2001
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
Classification of Neurons
–
Functional – based on the
direction of impulse
transmission
•
Sensory neurons
•
Motor neurons
•
Interneurons
(
association
)
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Functional Classification of Neurons
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
Starting
a
Nerve
Impulse
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•
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
The
Action
Potential
The
Action
Potential
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•
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
Nerve
Impulse
Propagation
Nerve
Impulse
Propagation
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•
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
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
How
Neurons
Communicate
at
Synapses
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Synapses
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
Neural Regeneration
Structure
of
a
Nerve
Structure
of
a
Nerve
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
•
Endoneurium
surrounds
each fiber
•
Groups of fibers are bound
into
fascicles
by the
perineurium
•
Fascicles are bound
together by
epineurium
Classification
of
Nerves
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