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Taylor DeLong
Mrs
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Introduction
A
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150,000 kilometers of myelinated nerve fibers
1
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Constantly develops new interactions
3
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Human body functions
1
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Chemical and electrical interactions within the brain are responsible for
memory of experiences and movements
3
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Neurons
b
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Stem cells
II
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Receive information, process information, and generate output
B
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Nucleus, golgi bodies, mitochondria, lysosomes, and endoplasmic
reticulum
2
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Mitochondria and smooth endoplasmic reticulum are distributed
among the neuron
4
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Microtubules, microfilaments, and neurofilaments make up the
cytoskeleton inside the cell and are responsible for maintaining the
unique neuronal shape
C
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Soma
a
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Dendrites
a
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Branch-like extensions that project from the soma
3
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Output unit of the cell, specialized to send information to other
neurons, muscle cells, or glands
b
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Presynaptic terminals
a
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Finger-like projections
5
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Chemicals from presynaptic terminals that release into the
synaptic cleft
b
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Synaptic cleft
a
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Serves as the site for interneuronal communication
D
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The cellular mechanism that transports substances along an axon
2
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Anterograde – moves neurotransmitters and other substances
from the soma down the axon toward the presynaptic terminal
b
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Both can occur at varieties of speeds
d
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Alzheimer’s disease
ii
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Amyotrophic lateral sclerosis
E
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Bipolar cells
a
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Have a single projection from the cell body that divides into
two axonal roots
ii
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Sensory neurons – bring information from the body into
the spinal cord
2
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Have multiple dendrites arising from many regions of the cell body
and a single axon
b
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Variety of different shapes and dendritic organizations
d
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IV
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Purkinje cells
i
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Receive up to 150,000 synapses on their expansive
dendritic trees
Transmission of information by neurons
A
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Na+, K+, Cl-, and Ca+ diffuse through open channels
2
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Gated channels open in response to a stimulus and close when the
stimulus is removed
4
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Ligand-gated channels open in response to a neurotransmitter binding
to the surface of a channel receptor on a postsynaptic cell membrane
a
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Result in the generation of local potentials
6
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Open almost instantaneously and close as quickly
b
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Electrical potentials
Resting membrane potential
A
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A steady state condition with no net flow of ions across the membrane
C
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Two forces act on ions to determine their distribution across the plasma
membrane
1
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Electrical gradient
E
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Equilibrium is reached when there is no net movement of the ion across the
membrane
G
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Electrochemical gradient and resting membrane potential
1
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2
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Na+-K+ pump
Changes from resting membrane potential
A
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Depolarized membrane – when the potential becomes less negative than the
resting potential
C
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The potential becomes more negative than the resting potential
2
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Modulation – involves small changes in the electrical potential of the membrane
that alter the flow of ions across a cell membrane
E
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Conduction originates with local potentials at the receiving sites of the
neuron
a
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In motor neurons and interneurons – receiving sites are on the
postsynaptic membrane
2
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Action potential – a brief, large depolarization in electrical potential that
is repeatedly regenerated along the length of an axon
4
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Allows an action potential to actively spread long distances
b
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Local potential developing into action potential
a
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Change in local membrane potential of the sensory ending
c
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Release of transmitter from the sensory neuron presynaptic
terminal
e
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Activation of synaptic potential in the postsynaptic membrane
F
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Receptor potentials/synaptic potentials
2
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Peripheral receptors
a
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Local receptor potentials are generated when the peripheral
receptors of a sensory neuron are stretched, compressed,
deformed, or exposed to thermal or chemical agents
c
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Local synaptic potentials
a
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Presynaptic neuron releases neurotransmitters
c
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Binding of neurotransmitter to receptors on the postsynaptic cell
opens ligand-gated ion channels
e
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Action of the neurotransmitter determines whether the synaptic
potential will be depolarizing or hyperpolarizing
5
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Spatial summation – the process by which receptor or synaptic
potentials generated in different regions of the neuron are added
together
G
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Actively propagated
2
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The meaning of the signal is determined by the neural pathway along
which it is conducted
4
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Stronger stimuli produce action potentials of the same voltage and
duration as are produced by minimally sufficient stimuli
H
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Sudden influx of Na+ through voltage-gated channels
2
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Axon hillock – the region closest to the synapse with a high density of
Na+ channels in interneurons and motor neurons
a
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Summation resulting in depolarization – the opening of many
voltage-dependent Na+ channels generates an action potential
c
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Threshold stimulus intensity – stimulus intensity that is just sufficient
to produce an action potential
a
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Many voltage-dependent Na+ channels open at -55mV
depolarization
c
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K+ leaves cell repelled by the positive electrical charge inside the
membrane when K+ channels open
e
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Refractory – channels become inactivated immediately after opening for an
action potential and require a specific amount of time before they can be
activated again for a subsequent action potential
1
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The membrane is unresponsive to stimuli
b
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Relative refractory period
a
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Membrane potential is returning toward its resting level and may
be hyperpolarized
c
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Propagation of action potentials
1
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Impulse is propagated by flipping of the polarity of the electrical signal
3
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The spread of depolarization is repeated along the length of the axon
5
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Structural adaptions that improve passive properties of fasterconduction axons
a
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A larger-diameter axon will allow greater current flow
ii
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VII
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Myelination
i
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Provides insulation, preventing current flow across the
axonal membrane
iii
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Fewer positive ions are deposited along the inner
membrane to depolarize the membrane to a threshold level
v
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Nodes of Ranvier
i
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Specialized for active propagation of an action potential by
allowing ion flow across the membrane
iii
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Causes action potential to slow down when crossing
d
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Action potential propagates down a myelinated axon and
appears to jump quickly from node to node
ii
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Propagation of the action potential in a myelinated axon
requires that a new action potential be generated at each
Node of Ranvier and passed down the axon
iv
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Afferent neurons
1
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Efferent neurons
1
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Interneurons
1
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Convergence
1
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Neural input to sensory association areas in the cerebral cortex
B
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IX
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The process whereby a single neuronal axon may have many branches
that terminate on a multitude of cells
2
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Form a critical support network for neurons
B
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Types of glia
a
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Microglia – small glial cells
C
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Astrocytes
a
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Have a direct role in cell signaling
c
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Spread Ca+ to neighboring astrocytes through openings from one
cell to another
e
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Do not have synapses and do not generate action potentials
g
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Connect neurons and blood capillaries, providing a nutritive
function for neurons
i
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Fill the communication gap between the neuron and
vascular smooth muscle cells
j
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Oligodendrocytes
a
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Schwann cells
a
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May wrap around one or more axons
c
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Microglial cells
1
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Act as immune system of CNS and clean the neural environment
3
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Clean up and remove debris from dying cells
Neuroinflammation: Beneficial and harmful effects

X
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Neuroinflammation
1
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Response is mediated by reactive microglia and astrocytes
3
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Myelin: Clinical application
A
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Peripheral neuropathy
a
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Involve destruction of myelin surrounding the largest sensory and
motor fibers
2
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Involves acute inflammation and demyelination of peripheral
sensory and motor fibers
b
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Preceded by an intestinal infection that activates the immune
system causing production of an antibody that mistakenly crossreacts with myelin
d
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Cranial nerves of the face may be affected
f
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Medical treatments
i
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Intravenous immunoglobulin therapy
B
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Damage to the myelin sheaths in the brain and spinal cord
2
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Causes slowed or blocked transmission of signals
4
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Weakness, lack of coordination, impaired vision, double vision,
impaired sensation, and slurred speech
b
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MS types
a
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During relapses, new signs and symptoms appear
ii
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XI
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Secondary progressive MS
i
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Continuous neurologic decline with fewer or no relapses
c
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Steady functional decline from time of onset with
predominantly spinal cord symptoms
d
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Begins with a steady functional decline with superimposed
relapses and partial remissions
ii
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Stem cells can give rise to different types of cells in the CNS with maturation and
differentiation
B
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Self-renew
2
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Populate developing and degenerating regions of the CNS
C
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Part of the hippocampus
2
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Constantly produce new neurons that are important in creating
neuronal networks in the brain
b
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Stem cells as brain cell implants
1
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Disease currently without effective treatments
2
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Use of neuronal stem cells following spinal cord injury



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