Transcript Nervous system

The Nervous System:
Neural Tissue
Chapter 13
Introduction
• Nervou
m
yste= control center
& communications
network
• Functions
– Stimulates
movements
– Maintains h
estai
om
(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
• Sen(orysafern
t)d
n
so
iv
• Nerve fibers that
carry information to
the central nervous
system
• Motor(efern
)t
• Nerve fibers that
carry information
from the central
nervous system
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Histology of Nervous Tissue
• 2 types of cells
– Neuro
n
s
• Structural & functional part of nervous system
• Specialized functions
– Neuorglia(glai)sec
• Gli = glue
• Support & protection of nervous system
Neuroglia
• Neuroglia of CNS
–
–
–
–
Astroscye
Olgio
d
steycn
r
Microglia
Epen
d
ascy
lm
Neuroglia of CNS
• Astrocytes
• Form theblo
d
-brain
e
b
• Structural
framework for CNS
• Repair damaged
neural tissue
• Control the intersia
l
en
virom
tof
the brain
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Neuroglia of CNS
• Oligodendrocytes
• Produce m
ataround
sh
yelin
nerve fibers in the
central nervous
system
Marieb, Essentials of Anatomy and Physiology, 8th edition, 2006
Neuroglia of CNS
• Microglia
• Spider-like p
agocytes
h
• Dispose of debris
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Neuroglia of CNS
• Ependymal cells
• Line ven
triclsof the brain and spinal cord
• Secrete cerb
d
alfu
in
osp
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Neuroglia of CNS
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neuroglia of PNS
• Schwancels
– Form myelin sheaths of PNS
• Satelics
Marieb, Essentials of Anatomy and Physiology, 8th edition, 2006
Neurons
• Function
– Conduct
electrical
impulses
• Structure
– Cell body
• Nucleus with
nucleolus
• Cytoplasm (perikaryon
)
– Cytoplasmic
processes
• Dendrites
• Ax
on
Human Anatomy, 3rd edition
Prentice Hall, © 2001
• Long, specialized
Axon Structure
– Colaters= branches
–T
elod
ria= termination of axons & collaterals
n
• Cytoplasm = axop
lsm
• Plasma membrane = a
lem
o
x
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
– Myex
n
o
atli
d
• Axon is surrounded by a myelin sheath
– Un
m
o
x
td
a
elin
y
• Axon has no myelin sheath
Myelin
• Whtem
iarof nerves, brain,
spinal cord
• Composed primarily
of p
slid
o
h
• Production
– Developing Schwann
cells wind around
axon
• Neurm
ile
a
– Peripheral
cytoplasmic layer of
the Schwann cell
enclosing the myelin
sheath
Marieb, Essentials of Anatomy and Physiology, 8th edition, 2006
A Myelinated Axon
• Function of myelin
– Increases speed of
impulse conduction
– Insulation and
maintenance of axon
• NodeofR
s anvier
– 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
– Sensoryn
eu
– Motorn
s
eu
– Intern
os(asociatn
u
)
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 anactio
l
ea
p
n
• Depends on the movement of sodiu
s(Na+) andpotasiu
on
m
n
m
(K+)
between the intersia
dand the inside of the neuron.
lfu
Restin
gPoten
ial
• 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 th
resold
Starting a Nerve Impulse
• Depolarizatio
n– 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
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
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
– Repolarizesthe membrane
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20lectures/nervous%20system/neuron6.gif
Return to Resting Potential
• Sod-m
iu
pou
p
m
sitarestores 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
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Continuation of the Nerve Impulse
Between Neurons
• Impulses are able to cross a sy
eto another nerve
p
a
n
– Neurotan
ieis released from
sm
theaxonterm
ial
into synap
ticlef
– The dendrite of the
next neuron has
receptors that are
stimulated by the
neurotransmitter
(synap
ticknob)
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Synaptic Cleft
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Postsynaptic Membrane Receptor
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
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 fa
lwhich are
sciu
bundled into n
ervs.
– Endon
rim
eu
surrounds eachnervfib
(axon)
– Groups of fibers are
bound into fascicles
• Surrounded by theperin
m
u
– Fascicles are bound
together into a nerve
• Surrounded by
the ep
rm
u
in
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006