Download Nervous system

The Nervous System:
Neural Tissue
Chapter 13
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
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Functional Classification of the
Peripheral Nervous System
• Sensory (afferent)
division
• Nerve fibers that
carry information to
the central nervous
system
• Motor (efferent)
• 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
– Neurons
• Structural & functional part of nervous system
• Specialized functions
– Neuroglia (glial cells)
• Gli = glue
• Support & protection of nervous system
Neuroglia
• Neuroglia of CNS
–
–
–
–
Astrocytes
Oligodendrocytes
Microglia
Ependymal cells
Neuroglia of CNS
• Astrocytes
• Form the bloodbrain barrier
• Structural
framework for CNS
• Repair damaged
neural tissue
• Control the
interstitial
environment of
the brain
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Neuroglia of CNS
• Oligodendrocytes
• Produce myelin
sheath around
nerve fibers in the
central nervous
system
Marieb, Essentials of Anatomy and Physiology, 8th edition, 2006
Neuroglia of CNS
• Microglia
• Spider-like
phagocytes
• Dispose of debris
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Neuroglia of CNS
• Ependymal cells
• Line ventricles of the brain and spinal cord
• Secrete cerebrospinal fluid
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006
Neuroglia of CNS
Human Anatomy, 3rd edition
Prentice Hall, © 2001
Neuroglia of PNS
• Schwann cells
– Form myelin sheaths of PNS
• Satellite cells
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
• Axon
Human Anatomy, 3rd edition
Prentice Hall, © 2001
• Long, specialized
Axon Structure
– Collaterals = branches
– Telodendria = termination of axons & collaterals
• Cytoplasm = axoplasm
• Plasma membrane = axolemma
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
Myelin
• White matter of
nerves, brain, spinal
cord
• Composed primarily
of phospholipids
• Production
– Developing Schwann
cells wind around
axon
• Neurilemma
– 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
• 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
• 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
– Sensory neurons
– Motor neurons
– Interneurons (association)
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 an action potential
• Depends on the movement of sodium ions
(Na+) and potassium ions (K+) between the
interstitial fluid and the inside of the
neuron.
Resting Potential
• 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 threshold
Starting a Nerve Impulse
• Depolarization – 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
– Repolarizes the
membrane
http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20lectures/nervous%20system/neuron6.gif
Return to Resting Potential
• Sodium-potassium
pump restores 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 synapse to another nerve
– Neurotransmitter
is released from
the axon terminal
(synaptic knob)
into synaptic cleft
– The dendrite of the
next neuron has
receptors that are
stimulated by the
neurotransmitter
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 fasciculi which
are bundled into
nerves.
– Endoneurium
surrounds each nerve
fiber (axon)
– Groups of fibers are
bound into fascicles
• Surrounded by the
perineurium
– Fascicles are bound
together into a nerve
• Surrounded by
the epineurium
Marieb, Essentials of Human Anatomy and Physiology, 8th edition, 2006