Brain Structures

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Brain Structures

• The brain is made of three main parts the
  forebrain, midbrain and hindbrain. The forebrain
  consists of the cerebrum, thalamus and
  hypothalamus (part of the limbic system).
• The Cerebrum is the largest part of the brain
  and is divided in to 4 lobes.

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Cerebral Cortex

• Frontal Lobe associated with reasoning,
  planning, parts of speech, movement, emotions and
  problem solving
• Parietal Lobe - associated with movement,
  orientation, recognition and perception of
  stimuli
• Occipital Lobe associated with visual
  processing
• Temporal Lobe associated with perception and
  recognition of auditory stimuli, memory and
  speech

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Note the cerebral cortex is highly wrinkled
which increases the surface area of the brain and
the amount of neurons within it.
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Action of Neurons

• A neuron affects other neurons by releasing a
  neurotransmitter that binds to chemical
  receptors.
• A neurotransmitter can be thought of as a key and
  the receptor as a lock.
• Receptors are
• Excitatory (causing increased firing rate)
• Inhibitory (causing decreased firing rate)
• Modulatory (causing long-lasting effects not
  directly related to firing rate)

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How Nerve Cells Talk

• Electrical signals travel from one nerve cell to
  another, causing the release of a
  neurotransmitter into a small gap between cells,
  called a synapse.

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How Nerve Cells Talk (cont)

• The neurotransmitter travels across the gap,
  binds to a protein on the receptor which causes
  change.
• The relationship between the receptor and
  neurotransmitter is specific to each other.
• A nerve cell (neuron) is a long, skinny cell with
  three prominent parts Dendrites, Nucleus and
  Axon
• Information flows through neurons starting in the
  dendrites and ending at the terminal part of the
  axon.
• After a short while in the synapse, the
  neurotransmitters that have been released are
  recalled into the axon in a process called
  re-uptake, so that they are available should
  the neuron need to fire again.

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How Nerve Cells Talk (cont)
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Alcohol and Neurotransmitter Interactions

• In order for Alcohol or drugs to have an effect
  on someone, it must first be taken into the
  bloodstream.
• Once in the blood, there is almost immediate
  access to the brain, interfering with
  communication between nerve cells and other
  cells.
• The activities of excitatory nerve pathways can
  be suppressed.
• The activities of the inhibitory nerve pathways
  can be increased.

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Alcohol and Neurotransmitter Interactions (cont)

• When alcohol consumption is abruptly reduced or
  discontinued, a withdrawal syndrome may follow.
  Symptoms include
• Seizures
• Tremors
• Hallucinations
• Insomnia
• Agitation
• Confusion

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Alcohol and Neurotransmitter Interactions (cont)

• Research suggests that alcohol affects multiple
  neurotransmitter systems in the brain.
• Virtually all brain functions depend on a
  delicate balance between excitatory and
  inhibitory neurotransmission.
• A detailed understanding of alcohols mechanism
  of action in the brain is a prerequisite to
  discovering effective treatments for both alcohol
  abuse and alcoholism.

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The Limbic System

• The limbic system is a group of brain structures
  organized into a functional unit that is
  important in the expression of emotion and mood
  states.
• It forms an integrated circuit surrounding the
  thalamus an important relay station between
  higher brain centers and the hind brain and
  spinal cord.
• The limbic system is thought to be important in
  emotional behaviors and in the expression of
  emotion related to euphoria and feelings of
  well-being. For these reasons, the limbic system
  may have an important role in drug abuse.

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Limbic System Components

• The general structure and components of the
  limbic system include the
• Amygdala
• Nucleus Accumbens
• Olfactory Tubercle
• Septal Nuclei
• Hippocampus
• Hypothalamus
• Cingulate Cortex
• Frontal Cortex

The separate components of the limbic system are
interconnected such that activity initiated in
one structure affects other components.
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The Role of the Limbic System in Behavior

• Some structures of the limbic system are
  important in reinforcement processes.
• The term reinforcement applies to processes
  perceived as rewarding or good, which therefore
  are repeated, such as electrical
  self-stimulation.
• Humans will choose to stimulate many of these
  same brain regions and report positive feelings
  of well-being and euphoria.
• The limbic system sites that produce these
  effects in the animals include the lateral
  hypothalamus, nucleus accumbens, frontal cortex,
  cingulate cortex and the brain-stem nuclei
  believed to be part of the limbic system these
  include the substantia nigra and ventral
  tegmental area, which both contain DOPAMINE
  neurons that send inputs to many limbic system
  components.
• The stimulation of each of these regions produced
  significant activation of several limbic-system
  structures.

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The Role of the Limbic System in Drug Use

• A large number of experiments have focused on
  identifying the brain circuits that mediate the
  reinforcing effects of abused drugs, because the
  reinforcing effects are responsible for drug
  abuse.
• It is clear that dopamine-containing neurons that
  project from the ventral tegmental area to the
  nucleus accumbens have a critical role in the
  reinforcing actions of COCAINE and AMPHETAMINE.
• The levels of glucose metabolism are
  significantly elevated in a number of limbic
  structures in animals self-administering cocaine
  intravenously. Other experiments have directly
  shown dopamine levels in the nucleus accumbens to
  be increased in animals intravenously
  self-administering cocaine.
• Collectively, these data imply an important role
  for the limbic system in general and specifically
  for dopamine neurons in the limbic system tied to
  the brain processes involved in stimulant abuse.

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Limbic System and Opiates/Alcohol

• The brain circuits involved in OPIATE
  reinforcement appear to be very similar to those
  mediating cocaine self-administration. Limbic
  structures are clearly implicated in opiate
  reinforcement, but a central role for dopamine is
  less obvious. Limbic structures also appear to
  be important for ethanol (drinking ALCOHOL)
  reinforcement.

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Limbic System Conclusion

• The limbic system plays an important role in
  behavior.
• The nucleus accumbens appears to be a structure
  central to the reinforcing properties of cocaine
  and amphetamine, but it appears less important to
  opiate and alcohol reinforcement.
• A more exact definition of specific
  neurochemicals and brain-cell pathways in the
  limbic system that are involved in drug abuse
  will become clearer as new methodologies are
  developed.