The Role of the Prefrontal Cortex and Hippocampus, Under Load, in a Delayed Nonmatch to Place Task

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Brain and Behavior

• Neural Conduction
• Synaptic Function

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Function

• What is the function of an action potential?
• - Communication
• In general, what is an action potential?
• - Electrical signal

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Overview

• 1) An excitatory or inhibitory neurotransmitter
  is released from presynaptic neurons
• 2) Information is integrated by the postsynaptic
  neuron
• 3) The neuron will or will not fire an action
  potential the All or None principal

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Cell Body Metabolic Fctns. Dendrites Receive
neurotransmitter Axon Hillock Region where
AP.emanates from Axon Process that AP is
propagated down Myelin Fatty insulation Nodes of
Ranvier Space between Myelin Buttons Neurotransmi
tter release
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Neural Communication

• Resting Potential
• Action Potential
• Neural Integration

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Resting Potential
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() Positive Potential
(-) Negative Potential
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TWO forces influence ion movement across membrane
The Action Potential

• Electrical force (determined by the voltage
  difference across the membrane) and
• Diffusion force (determined by the concentration
  difference of ions across the membrane).

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Diffusion Force
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Electrical Force
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Forces acting on ions

• () charged ions on the outside of the cell are
  attracted into the cell by the electrical force
• In the resting state, there are more () charged
  ions on the outside of the cell than on the
  inside of the cell, so () ions are also pushed
  into the cell by the diffusion force.
• (-) charged ions, are repelled outward by the
  electrical force. There are more (-) charged ions
  on the inside of the cell than on the outside of
  the cell, so (-) ions are also pushed out of the
  cell by the diffusion force.

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Myelin
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? The action potential is transmitted along the
myelinated axon At 225 mph. (1-100 m/sec) In an
unmyelinated axon, it is about 2 mph
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Saltatory Conduction
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Refractory Period

• Absolute - A brief period of time ( 1 msec)
  after a neuron fires an action potential in which
  it is impossible to make the neuron fire another
  action potential

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Neurotransmitters -Why are they important?

• Widely influence CNS function
• Modulate neuronal activity
• Implicated in a sig. Number of neuropsychiatric
  and neurological disorders
• - Parkinsons disease
• - Schizophrenia
• - Tourettes Syndrome
• - Tardive Dyskinesia
• - Depression

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Neurotransmission

• Each nerve terminal releases many chemicals and
  perhaps even more than one n.t.
• Cellular responses vary from changing ion fluxes
  to altering genetic expression
• Mood, memory, cognition, thought processes, and
  behavior can be manipulated by pharmacological
  intervention
• 100s of neurotransmitters/neuromodulators exist
  in the brain

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Steps in synaptic transmission

• Neurotransmitter is synthesized and packaged into
  vesicles.
• An action potential is propagated down the axon
  to the presynaptic boutons.
• 2. Depolarization causes opening ion channels.
• 3. Neurotransmitter filled vesicles to fuse with
  the membrane.
• 4. Neurotransmitter is released into cleft and
  binds to receptors on postsynaptic cell
• 5. This opens or closes postsynaptic ion channels
  and Postsynaptic current flows inside post
  synaptic cell(increasing or decreasing the
  likelihood of an AP)
• 6. Breakdown, diffusion, or reuptake of NT

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Synaptic Physiology
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Synaptic Physiology
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Production, Storage, Release, Removal
Most small neurotransmitters are produced in the
synaptic buttons through a synthesis process that
typically employs an enzyme
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Enzymes
Essentially all chemical reactions in cells are
mediated by enzymes or catalysts.  A catalyst
acts by bringing together the reactants, and
thereby increasing the rate of a chemical
reaction, without being permanently changed in
the reaction.
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Production, Storage, Release, Removal
Most small neurotransmitters are stored in
synaptic vesicles at the boutons
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Production, Storage, Release, Removal
Most small neurotransmitters are released through
exocytosis
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Production, Storage, Release, Removal
reuptake transporters in the terminals take the
neurotransmitter back inside the neuron to be
re-packaged or degraded enzymatic degradation
enzymes found in the synaptic cleft break down
the neurotransmitter after it is
released diffusion neurotransmitters simply
move out of the synaptic cleft
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Synaptic Physiology
Reuptake
Diffusion
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Antidepressants

• Mood Tx
• (MAOI) monoamine oxidase inhibitors increases
  the available amount of dopamine, serotonin, and
  norepinephine
• Tricyclics Block reuptake of serotonin and
  epinephrine
• SSRIs slectively block reuptake of serotonin

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Synaptic Physiology
Ligands Endogenous Exogenous
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Agonists and Antagonists

• Agonist (Greek Agon, meaning contest)
• Drugs that facilitate post-synaptic effects
• Antagonist
• Drugs that inhibit or block the post-synaptic
  effects

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Monoamines -Catacholamines

• Of the 100 billion neurons in the brain, only
  500,000 are estimated to use catecholamines
  (.0005), yet more research has been devoted to
  them than any other.
• Dopamine (DA)
• Norepinephrine (NE) also noradrenalin
• Epinephrine

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Monoamines -Catacholamines

• Neurotransmitter Dopamine
• Function Involved in reward, cognition, and
  motor processes
• Removal broken down by Presynaptic reuptake
• Modulation haliperidol (antagonist)
  antipsychotic

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Monoamines -Catacholamines

• Neurotransmitter Norepinephrine
• Function Attention, arousal, vigilance
• Removal Presynaptic reuptake
• Modulation propanolol (antagonist)
  antihypertensive (a.k.a. beta blocker)

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Monoamines -Indolaamines

• Neurotransmitter Serotonin
• Function homeostasis (eat, sleep, reproduction)
  mood
• Removal Presynaptic reuptake
• Modulation prozac (agonist)
• antidepressant/anxiolytic

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Acetylcholine

• Neurotransmitter Acetylcholine
• Function muscle contraction, memory,
• attention,
• Removal reuptake
• Modulation botulis toxin (antagonist) Blocks
  release of acetylcholine (paralysis)