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Copyright 2010, John Wiley & Sons, Inc.
Chapter 9
Nervous Tissue
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Copyright 2010, John Wiley & Sons, Inc.
End of Chapter 9
Copyright 2010 John Wiley & Sons, Inc.
All rights reserved. Reproduction or translation of this
work beyond that permitted in section 117 of the 1976
United States Copyright Act without express permission
of the copyright owner is unlawful. Request for furtherinformation should be addressed to the Permission
Department, John Wiley & Sons, Inc. The purchaser may
make back-up copies for his/her own use only and not
for distribution or resale. The Publishers assumes noresponsibility for errors, omissions, or damages caused
by the use of theses programs or from the use of the
information herein.
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Copyright 2010, John Wiley & Sons, Inc.
Structures of the Nervous System
Brain: neurons enclosed within skull
Spinal cord:connects to brain and enclosedwithin spinal cavity
Nerves: bundles of many axons of neurons
Cranial nerves (12 pairs) emerge from brain Spinal nerves (31 pairs) emerge from spinal cord
Ganglia: groups of neuron cell bodies locatedoutside of brain and spinal cord
Enteric plexuses:networks in digestive tract Sensory receptors:monitor changes in internal
or external environments
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Structures of the Nervous System
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Functions of the Nervous System
Sensory receptors and sensory nerves Carry information into brain and spinal cord
Integration: information processing
Perception = awareness of sensory input
Analyzing and storing information to help lead to
appropriate responses
Motor activity: efferent nerves
Signals to muscles and glands (effectors)
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Copyright 2010, John Wiley & Sons, Inc.
Organization of the Nervous System
Central Nervous System (CNS) Brain and spinal cord
Peripheral Nervous System (PNS)
All nervous system structures outside of the CNS
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Copyright 2010, John Wiley & Sons, Inc.
Histology of the Nervous System
Neurons Can respond to stimuli and convert stimuli to
electrical signals (nerve impulses) that travel along
neurons
Neuroglia cells: support, nourish and protectneurons
Neuroglia critical for homeostasis of interstitial fluid
around neurons
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Neuronal Structure
Cell body: nucleus, cytoplasm with typicalorganelles
Dendrites: highly branched structures that
carry impulses to the cell body
Axon: conducts away from cell body toward
another neuron, muscle or gland
Emerges at cone-shaped axon hillock
Axon terminals: contain synaptic vesiclesthat can release neurotransmitters
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Neuronal
Structure
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Structural Classes of Neurons
Multipolar
Have several or many dendrites and one axon
Most common type in brain and spinal cord
Bipolar
Have one dendrite and one axon
Example: in retina of eye and inner ear
Unipolar
Have fused dendrite and axon Sensory neurons of spinal nerves
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Copyright 2010, John Wiley & Sons, Inc.
Functional Classes of Neurons
Sensory (afferent)
Convey impulses into CAN (brain or spinal cord)
Motor (efferent)
Convey impulses from brain or spinal cord out
through the PNS to effectors (muscles or glands)
Interneurons (association neurons)
Most are within the CNS
Transmit impulses between neurons, such asbetween sensory and motor neurons
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Copyright 2010, John Wiley & Sons, Inc.
Neuroglia
Cells smaller but much more numerous thanneurons
Can multiply and divide and fill in brain areas
Gliomas: brain tumors derived from neuroglia
Functions
Do not conduct nerve impulses
Do support, nourish and protect neurons
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Neuroglia
Astrocytes: help form blood brain barrier
Oligodendrocytes: produce myelin in CNS
Microglia: protect CNS cells from disease
Ependymal cells: form CSF in ventricles
Schwann: produce myelin around PNS
neurons; help to regenerate PNS axons
Satellite cells: support neurons in PNS ganglia
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Copyright 2010, John Wiley & Sons, Inc.
Myelination
Axons covered with a myelin sheath Many layers of lipid and protein: insulates neurons
Increases speed of nerve conduction
Appears white (in white matter)
Nodes of Ranvier: gaps in the myelin
Nodes are important for rapid signal conduction
Some diseases destroy myelin:
Multiple sclerosis
Tay-Sachs
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Collections of Nervous Tissue
Clusters of neuron cell bodies
Ganglion: cluster of cell bodies in PNS
Nucleus: cluster of cell bodies in CNS
Bundles of axons
Nerve: bundle of axons in PNS
Tract: bundle to axons in CNS
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Gray and White Matter
White matter: primarily myelinated axons
Gray matter: cell bodies, dendrites,
unmyelinated axons, axon terminals, neuroglia
Locations of gray and white matter
Spinal cord: white matter (tracts) surround centrally
located gray matter H of butterfly
Brain: gray matter in thin cortex surrounds white
matter (tracts)
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Neuron Regeneration
Regeneration of PNS neuronsAxons and dendrite in the PNS can be repaired if
cell body is intact and Schwann cells functional.
These form a regeneration tube and grow axons
or dendrites if scar tissue does not fill the tube Regeneration of CNS neurons
Very limited even if cell body is intact
Inhibited by neuroglia and by lack of fetal growth-stimulators
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Copyright 2010, John Wiley & Sons, Inc.
Organization of the Nervous System
Central nervous system (CNS) structures: Brain
Spinal cord
Peripheral nervous system (PNS) structures: Cranial nerves and branches
Spinal nerves and branches
Ganglia
Sensory receptors
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Organization of the Nervous System
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Organization of the Nervous System
Peripheral nervous system (PNS) divisions Somatic (SNS)
Sensory neurons from head, body wall, limbs, special
sense organs
Motor neurons to skeletal muscle: voluntary
Autonomic (ANS) nervous systems Sensory neurons from viscera
Motor neurons to viscera (cardiac muscle, smooth
muscle, glands): involuntary
Sympathetic: fight-or-flight
Parasympathetic: rest-and-digest
Enteric nervous system (ENS): brain of the gut
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Copyright 2010, John Wiley & Sons, Inc.
Organization of the Nervous System
Peripheral nervous system (PNS), Enteric nervous system (ENS): brain of the gut
Sensory neurons monitor chemical changes and
stretching of GI wall
Motor neurons regulate contractions, secretions and
endocrine secretions (involuntary)
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Copyright 2010, John Wiley & Sons, Inc.
Structure and Function of the Nervous SystemInteractions Animation
Introduction to Structure and Function of the
Nervous System
You must be connected to the internet to run this animation.
http://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_struct_nerv_sys/anim_struct_nerv_sys/screen0.swfhttp://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_struct_nerv_sys/anim_struct_nerv_sys/screen0.swfhttp://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_struct_nerv_sys/anim_struct_nerv_sys/screen0.swfhttp://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_struct_nerv_sys/anim_struct_nerv_sys/screen0.swf8/13/2019 Ch0 Nervous Tissue
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Copyright 2010, John Wiley & Sons, Inc.
Action Potentials
Action potentials = nerve impulses
Require
A membrane potential: a charge difference across
cell membrane (polarization)
Ion channels: allow ions to move by diffusion fromhigh to low concentration
Leakage channels: allow ions to leak through membrane;
there are more for K+than for Na+
Gated channels Open and close on command
Respond to changes in membrane so can generate and
conduct action potentials
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Copyright 2010, John Wiley & Sons, Inc.
Resting Membrane Potential Typically70 mV
Inside of membrane more negative than outside
Caused by presence of ions: Inside (more negative) because cytosol has:
Many negative ions (too large to leak out): amino acids
(in cellular proteins) and phosphates (as in ATP)
K+ that easily leaks out through many K+ channels
Outside (more positive) because interstitial fluidhas:
Few negative ions Na+that does not leak out of cell: few Na+ channels
Membrane pumps that quickly pump out Na+ thatdoes leak (diffuse) into cell
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Copyright 2010, John Wiley & Sons, Inc.
Resting Membrane Potential
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Copyright 2010, John Wiley & Sons, Inc.
Action Potential
Series of events that activate cell membrane
in neuron or muscle fiber
An initial event (stimulus) is required
Triggers resting membrane to become more
permeable to Na+
Causes enough Na+to enter cell so that cell
membrane reaches threshold (~55 mv)
If so, the following events occur: action potentialwhich spreads along neuron or muscle fiber
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Copyright 2010, John Wiley & Sons, Inc.
Action Potential Depolarizing phase
Na+channels openas more Na+enters cell,
membrane potential rises and becomes positive
(700+ 30 mv)
Repolarizing phase K+channels openas more K+leave cell,
membrane potential is returned to resting value
(+ 30070 mv)
May overshoot: hyperpolarizing phase
Typically depolarization and repolarization take
place in about 1 millisecond (1/1000 sec)
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Copyright 2010, John Wiley & Sons, Inc.
Action Potential
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Copyright 2010, John Wiley & Sons, Inc.
Action Potential
Recovery
Levels of ions back to normal by action of Na+/K+
pump
Refractory period (brief): even with adequate
stimulus, cell cannot be activated All-or-none principle
If a stimulus is strong enough to cause
depolarization to threshold level, the impulse will
travel the entire length of the neuron at a constant
and maximum strength.
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Membrane PotentialsInteractions Animations
Membrane Potentials
You must be connected to the internet to run this animation.
http://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_memb_potential/anim_memb_potential/screen0.swfhttp://www.wiley.com/college/tortora/0470230169/interactions_animations/anim_memb_potential/anim_memb_potential/screen0.swf8/13/2019 Ch0 Nervous Tissue
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Copyright 2010, John Wiley & Sons, Inc.
Conduction of Nerve Impulses
Nerve impulse conduction (propagation) Each section triggers the next locally as even more
Na+channels are opened (like row of dominos)
Types of conduction
Continuous conduction In unmyelinated fibers; slower form of conduction
Saltatory conduction In myelinated fibers; faster as impulses leap between
nodes of Ranvier
Factors that increase rate of conduction Myelin, large diameter and warm nerve fibers
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Conduction
of Nerve
Impulses
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Copyright 2010, John Wiley & Sons, Inc.
Conduction
of Nerve
Impulses
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Copyright 2010, John Wiley & Sons, Inc.
Synaptic Transmission
Similar sequence of events occurs at Synapse (neuron-neuron)
Neuromuscular junction (neuron-muscle fiber:chapter 8)
Neuroglandular junction (neuron-gland)
Triggered by action potential (nerve impulse)
Components of synapse:
Sending neuron: presynaptic neuron (releases
neurotransmitter) Space between neurons: synaptic cleft
Receiving neuron: postsynaptic neuron
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Copyright 2010, John Wiley & Sons, Inc.
Synaptic Transmission
Action potential arrives at presynaptic
neurons end bulb
Opens voltage gated Ca2+channelsCa2+
flows into presynaptic cytosol
Increased Ca2+concentrationexocytosis
of synaptic vesicles
Neurotransmitter (NT) released into cleft
NT diffuses across cleft and binds toreceptors in postsynaptic cell membrane
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Copyright 2010, John Wiley & Sons, Inc.
Synaptic Transmission
NT serves as chemical trigger (stimulus) of
ion channels
Postsynaptic cell membrane may bedepolarized or hyperpolarized
Depends on type of NT and type of postsynapticcell
1000+ neurons converge on synapse; the sum ofall of their NTs determines effect
If threshold reached, then postsynaptic cellaction potential results
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Copyright 2010, John Wiley & Sons, Inc.
Synaptic Transmission
One-way transmission only because
Only presynaptic cells release NT
Only postsynaptic cells have receptors for NT
binding
Finally, NT must be removed from the cleft.Three possible mechanisms
Diffusion out of cleft
Destruction by enzymes (such as ACh-ase) in cleft
Transport back (recycling) into presynaptic cell
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Copyright 2010, John Wiley & Sons, Inc.Copyright 2009 John Wiley & Sons, Inc. 38
Signal Transmission at the Chemical
Synapse
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Copyright 2010, John Wiley & Sons, Inc.
Neurotransmitters
Acetylcholine (ACh): common in PNS Stimulatory (on skeletal muscles)
Inhibitory (on cardiac muscle)
Amino acids
Glutamate, aspartate, gamma aminobutyric acid(GABA), glycine
Modified amino acids
Norepinephrine (NE), dopamine (DA), serotonin
Neuropeptides such as endorphins
Nitric oxide (NO)
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End of Chapter 9
Copyright 2010 John Wiley & Sons, Inc.
All rights reserved. Reproduction or translation of this
work beyond that permitted in section 117 of the 1976
United States Copyright Act without express permission
of the copyright owner is unlawful. Request for furtherinformation should be addressed to the Permission
Department, John Wiley & Sons, Inc. The purchaser may
make back-up copies for his/her own use only and not
for distribution or resale. The Publishers assumes noresponsibility for errors, omissions, or damages caused
by the use of theses programs or from the use of the
information herein.