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Psychology 210
Cellular Anatomy
Lecture 2
Cells of the Nervous System
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Neurons
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Information processing and communicating nerve
cells
Glia
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Addressed later
What do you know about neurons
coming into this class?
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How does a neuron communicate with another
neuron?
What type of signal is processed in a neuron?
What are the parts of a neuron?
Parts of a Neuron
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3 main parts
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Dendrites
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Soma (cell body)
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Receive information
Cellular maintenance
Axon
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Transmits information
Dendrites
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Tree like processes
Receives information from other neurons
Dendritic spines
Create more area for axons to transmit information
 Change depending on the amount of activity
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This is one of the suggested bases for learning and
memory
A neuron can have multiple dendrites
The soma
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Nucleus- contains DNA
Nucleolus- constructs
ribosomes
Endoplasmic reticulumcontains ribosomes that
construct proteins
Golgi apparatus- “packages”
proteins
Mitochondria- produces
energy
The Axon
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Transmits information to
other neurons
Myelin sheath
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insulation that aids in the speed
of the neural transmission
Axon terminal
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End of the axon
Contains neurotransmitters
Also called terminal buttons
More on the Axon
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Axon hillock
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Where the action
potential begins
Nodes of Ranvier
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Segments of bare axon
not covered by myelin
Giant Squid
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Used to study
axons in the
1930s-1940s
Extra large axon
visible to the eye
Doesn’t have
myelin, so it is
extra large to add
conductance
Characterization of neurons
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Sensory neurons
 Translates incoming sensory
information into an electrical signal
Afferent Neurons
 Conduct information towards the
brain from the muscles and senses
Interneurons
 Neurons in the spinal cord and the
brain that both communicate a
signal and process that signal
Efferent Neurons
 Conduct information away from
the brain to the muscles and senses
Motor Neurons
 Translates electrical signal to the
muscles and glands
Not all neurons look the same
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Named by the number of
extensions from the cell
body
Unipolar
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Bipolar
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One extension that
branches into dendrites and
an axon
Two extensions: one axon
and one dendrite
Multipolar
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Many extensions: one axon,
many dendrites
Unipolar Neurons
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Found primarily in
human embryos and
invertebrates
Sensory neurons that
conduct impulses into
the brain
Bipolar Neurons
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Found primarily as
sensory neurons in
vision, audition and
olfaction
Multipolar neurons
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Found everywhere else
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Brain
Peripheral autonomic
nervous system
Spinal cord
What happens in a nerve
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Neurons communicate information to other neurons
The signal itself is an electrical signal within the
neuron
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Action Potential
From neuron to neuron, communication is chemical
The Resting Potential
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Two forces at work in a
neuron
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Force 1: Equilibrium: the
idea that the
concentration of a
molecule tries to remain
constant throughout the
medium (substance)
Potassium Ions
The Resting Potential
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Ex. Smells: the garbage begins to smell in one
spot, but the smell slowly expands throughout
the house
The smell gets lighter and lighter as it expands
throughout the house
 It tries to spread out as evenly as possible
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Status of the main players (ions)
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Sodium (Na+): more of it outside of the neuron
Potassium (K+): more of it inside of the neuron
Chloride (Cl-): more of it outside of the neuron
Based on equilibrium…
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What does Na+, K+, and Cl- want to do? Are
they “happy” where they are?
What direction will they move if allowed?
Due to equilibrium…
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Na+ wants to move inside the neuron
K+ wants to move outside the neuron
Cl- wants to move inside the neuron
What about charge?
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Does charge play a role in things?
According to charge, how might the ions react?
How do charges react to each other?
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Opposites attract
Like charges repel
One more piece to the puzzle
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There are large molecules inside the neuron with
negative charges
Now which way do the ions want to
go?
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Potassium:
Which way does equilibrium push?
 What about the charge?
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Now which way do the ions want to
go?
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Chloride:
Which way does equilibrium push?
 What about the charge?
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Now which way do the ions want to
go?
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Sodium:
Which way does equilibrium push?
 What about the charge?
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At rest
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Resting potential
-70mV
 Potassium can cross the membrane
 Sodium and Chloride cannot cross the membrane
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What will
potassium
want to do
at rest?
Stimulation
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When
stimulated by
another
neuron, some
Na+ channels
are opened
K+ channels
close
The action potential
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If the signal is
strong enough, it
makes it to the axon
hillock
If strong enough,
an action potential
is generated
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Threshold
Begins an action
potential
The action potential
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Depolarization:
occurs when Na+
flows into the cell
to Na+
channels opening
 Due
The action potential
At the beginning of the AP, Na
channels open and Na enters
the cell
Now, there is more of a positive charge
inside than outside (the Na stops coming in
for the same reasons the K did originally, a
balance of two forces) this represents the
peak of the AP
How’s potassium feeling now?
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Sodium moving
inside the cell made
the inside of the cell
more positive
This repels
potassium to move
outside
The action potential
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K+ channels open at the peak and K+ flows out of the
cell
This repolarizes the cell and even overshoots the
resting potential of before
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Called hyperpolarization
Then the Na/K pump brings the K back inside the cell
and the Na back outside the cell
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2 K for every 3 Na
Uses energy (ATP)
The action potential
At the peak, K+
channels open and
K+ exits the cell
Conditions are now back where they
started in terms of potential and charge,
but the ions are in opposite positions
The action potential
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The Sodium
Potassium pump
restores the original
environment of the
resting potential so
that the neuron can
fire yet again
This is known as the
refractory period
Graded Potentials
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Action Potentials are
referred to as “all-ornone”
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Either get an action
potential or not
Inputs that don’t reach
threshold: Graded
Potentials
Can add up across
synapses/inputs to reach
threshold
Saltatory Conduction
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Insulation is not perfect
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Signal loses strength down the axon
Regeneration of the Action Potential occurs at each break in
the myelin
At the Axon Terminal
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Vesicles containing
neurotransmitters are present
When an action potential
reaches the axon terminal,
Ca2+ channels open up and
this causes the fusing of the
vesicles to the membrane and
the release of the
neurotransmitters into the
synaptic cleft
In the Synaptic Cleft
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Neurotransmitters cross the
membrane and bind to receptors
on the receiving neuron
Depending on the
neurotransmitter, it can either
excite or inhibit the post-synaptic
neuron
Excitatory Postsynaptic Potential
(EPSP)- the excitation of the
receiving neuron
Inhibitory Postsynaptic Potential
(IPSP)- the inhibition of the
receiving neuron
Neurotransmitters
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Various chemicals
Can either excite the receiving neuron or inhibit
it
Acetylcholine- an excitatory NT typically found
in the muscles
GABA- an inhibitory NT typically found
elsewhere in the nervous system
How transmission occurs
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Multiple synapses on each neuronal dendrite
Some can excite while others inhibit
Axon potentials can be created by multiple
EPSPs from multiple neurons
Called Spatial Summation
How transmission occurs
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One synapse can fire repeatedly on the same
dendrite within a short temporal window (time
period)
Axon potentials can be created by multiple
EPSPs from a single neuron
Called Temporal Summation
Summary: One last thing
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Transmission within the neuron is electric
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Via action potentials
Transmission between neurons is chemical
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Via neurotransmitters
Glial cells
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Astrocytes- structural
support and blood brain
barrier
Oligodendrocytesmyelination of axons
CNS
Schwann cellsmyelination of axons
PNS
Microglia- clean up