Download cont`d. - PSY388

Chapter 3
Communication at
Synapses
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The Concept of the Synapse
• Neurons communicate by transmitting
chemicals at junctions, called “synapses”
– In 1906, Charles Scott Sherrington coined
the term synapse to describe the
specialized gap that existed between
neurons
• Sherrington’s discovery was a major feat
of scientific reasoning
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The Properties of Synapses
• Sherrington investigated how neurons
communicate with each other by studying
reflexes (automatic muscular responses to
stimuli)
• Example:
– Leg flexion reflex: a sensory neuron
excites a second neuron, which excites a
motor neuron, which excites a muscle
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Properties of Synapses (cont’d.)
• Sherrington found the same reflexive
movements after he made a cut that
disconnected the spinal cord from the brain.
• Evidently, the spinal cord controlled the
flexion and extension reflexes
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The Properties of Synapses (cont’d.)
• Sherrington observed three important points
about reflexes:
– Reflexes are slower than conduction along
an axon
– Several weak stimuli presented at slightly
different times or slightly different locations
produces a stronger reflex than a single
stimulus does
– As one set of muscles relaxes, another set
becomes excited
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The Properties of Synapses (cont’d.)
• Sherrington observed a difference in the
speed of conduction in a reflex arc from
previously measured action potentials
– He believed the difference must be
accounted for by the time it took for
communication between neurons
– Evidence validated the idea of the synapse
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The Properties of Synapses (cont’d.)
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The Properties of Synapses (cont’d.)
• Repeated stimuli over a short period of time
produced a stronger response (Sherrington)
• This led to the idea of temporal summation
– Repeated stimuli can have a cumulative
effect and can produce a nerve impulse
when a single stimuli is too weak
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The Properties of Synapses (cont’d.)
• Several small stimuli on a similar
location produced a reflex when a
single stimuli did not (Sherrington)
• Spatial summation: synaptic input
from several locations can have a
cumulative effect and trigger a nerve
impulse
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The Properties of Synapses (cont’d.)
• Presynaptic neuron: neuron that delivers the
synaptic transmission
• Postsynaptic neuron: neuron that receives
the message
• Excitatory postsynaptic potential (EPSP):
graded potential that decays over time and
space
• The cumulative effect of EPSPs are the basis
for temporal and spatial summation
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© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Properties of Synapses (cont’d.)
• Spatial summation is critical to brain
functioning
• Each neuron receives many incoming axons
that frequently produce synchronized
responses
• Temporal summation and spatial summation
ordinarily occur together
• The order of a series of axons influences the
results
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The Properties of Synapses (cont’d.)
• Sherrington also noticed that during the reflex
that occurred, the leg of a dog that was
pinched retracted while the other three legs
were extended
– He suggested that an interneuron in the
spinal cord sent an excitatory message to
the flexor muscles of one leg and an
inhibitory message was sent to the other
three legs
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The Properties of Synapses (cont’d.)
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The Properties of Synapses (cont’d.)
• This led to the idea of inhibitory postsynaptic
potential or the temporary hyperpolarization
of a membrane
– An ISPS occurs when synaptic input
selectively opens the gates for positively
charged potassium ions to leave the cell or
negatively charged chloride ions to enter
the cells
– Serves as an active “brake” that
suppresses excitation
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Figure 3.7 Sherrington’s Inference of Inhibitory Synapses
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Relationship Among EPSP, IPSP, and
Action Potentials
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Relationship Among EPSP, IPSP, and
Action Potentials (cont’d.)
• Sherrington assumed that synapses produce
on and off responses
• Synapses vary enormously in their duration of
effects
• Many inputs interact in ways that are not quite
additive. The effect of two synapses at the
same time can be more than double the
effect of either one, or less than double
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Relationship Among EPSP, IPSP, and
Action Potentials (cont’d.)
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Relationship Among EPSP, IPSP, and
Action Potentials (cont’d.)
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Relationship Among EPSP, IPSP, and
Action Potentials (cont’d.)
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Relationship Among EPSP, IPSP, and
Action Potentials (cont’d.)
• The spontaneous firing rate refers to the
periodic production of action potentials
despite synaptic input
• EPSPs increase the number of action
potentials above the spontaneous firing rate
• IPSPs decrease the number of action
potentials below the spontaneous firing rate
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The Discovery of Chemical
Transmission at Synapses
• German physiologist Otto Loewi was the first
to convincingly demonstrate that
communication across the synapse occurs
via chemical means
• Neurotransmitters are chemicals that travel
across the synapse and allow communication
between neurons
• Chemical transmission predominates
throughout the nervous system
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The Sequence of Chemical Events at
the Synapse
• The major sequence of events allowing
communication between neurons across the
synapse:
– The neuron synthesizes chemicals that
serve as neurotransmitters
– Action potentials travel down the axon
– Released molecules diffuse across the
cleft, attach to receptors, and alter the
activity of the postsynaptic neuron
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• Sequence of events (cont’d.)
– The neurotransmitter molecules separate
from their receptors
– The neurotransmitters are taken back into
the presynaptic neuron for recycling or
diffuse away
– The postsynaptic cell may send reverse
messages to slow the release of further
neurotransmitters by presynaptic cells
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© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• Major categories of neurotransmitters include
the following:
– Amino acids
– Monoamines
– Acetylcholine
– Neuropeptides
– Purines
– Gases
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The Sequence of Chemical Events at
the Synapse (cont’d.)
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• Neurons synthesize neurotransmitters and
other chemicals from substances provided by
the diet
– Acetylcholine synthesized from choline
found in milk, eggs, and nuts
– The amino acid tryptophan serves as a
precursor for serotonin
• Catecholimines contain a catechol group and
an amine group (epinephrine, norepinephrine,
and dopamine)
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• Vesicles: tiny spherical packets located in the
presynaptic terminal where neurotransmitters
are held for release
• MAO (monoamine oxidase): a chemical that
breaks down excess levels of some
neurotransmitters
• Exocytosis: refers to the excretion (release) of
the neurotransmitter from the presynaptic
terminal into the synaptic cleft
– Triggered by an action potential arriving
from the axon
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• Transmission across the synaptic cleft which is only
20 to 30 nanometers wide by a neurotransmitter
takes fewer than .01 microseconds
• Most individual neurons release at least two or
more different kinds of neurotransmitters
• The combination makes the neuron’s message
more complex, such as brief excitation followed by
prolonged inhibition
• Neurons may also respond to more types of
neurotransmitters than they release
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• The effect of a neurotransmitter depends on
its receptor on the postsynaptic cell
• An ionotropic effect refers to when a
neurotransmitter attaches to receptors and
immediately opens ion channels
• Transmitter-gated or ligand-gated channels
are channels controlled by a neurotransmitter
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• Most effects occur very quickly (sometimes
less than a millisecond after attaching) and
are very short lasting (e.g., half-life 5 ms)
• Most ionotropic effects rely on glutamate or
GABA (gamma-amino-butyric acid)
• Most of the brain’s excitatory ionotropic
synapses use the neurotransmitter glutamate.
• Most of the inhibitory ionotropic synapses
use GABA, which opens chloride gates,
enabling chloride ions, with negative charge
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© Argosy Publishing, Inc.
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• Metabotropic effects occur when
neurotransmitters attach to a receptor and
initiates a sequence of slower (after about 30
ms) and longer lasting metabolic reactions
(about a few seconds)
• Metabotropic synapses use many
neurotransmitters such as dopamine,
norepinephrine, serotonin, and sometimes
glutamate and GABA
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• When neurotransmitters attach to a metabotropic
receptor, it bends the receptor protein that goes
through the membrane of the cell
– Bending allows a portion of the protein inside
the neuron to react with other molecules
• Metabotropic events include behaviors as taste,
smell, and pain (exact timing not important)
• For vision and hearing, the brain needs rapid,
information (ionotropic events)
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© Argosy Publishing, Inc.
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• The portion inside the neuron activates a Gprotein: one that is coupled to guanosine
triphosphate (GTP), an energy storing
molecule
• G-protein increases the concentration of a
“second-messenger”
• The second messenger communicates to
areas within the cell
– May open or close ion channels, alter
production of activating proteins, or
activate chromosomes
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• Metabotropic effects utilize a number of
different neurotransmitters
• Neuropeptides are often called
neuromodulators
– Release requires repeated stimulation
– Released peptides trigger other neurons to
release same neuropeptide
– Diffuse widely and affect many neurons via
metabotropic receptors
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The Sequence of Chemical Events at
the Synapse (cont’d.)
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• General rule: a neuron delivers neuropeptides
that diffuse to receptors throughout a wide area,
but delivers other transmitters in small amounts
directly adjacent to their receptors
• Neuropeptides are important for hunger, thirst,
intense pain, and other long-term changes in
behavior and experience
• Video:
https://www.youtube.com/watch?v=ihxhpCkgkk0
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• A hormone is a chemical secreted by a gland or
other cells that is transported to other organs by
the blood where it alters activity
• Endocrine glands are responsible for the
production of hormones
• Hormones are important for triggering longlasting changes in multiple parts of the body
• For example, birds that are preparing for
migration secrete hormones that change their
eating and digestion to store extra energy for a
long journey.
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• Protein hormones and peptide hormones are
composed of chains of amino acids and
attach to membrane receptors where they
activate second messenger systems
• Hormones secreted by the brain can control
the release of other hormones
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• The pituitary gland is attached to the
hypothalamus and consists of two distinct
glands that each release a different set of
hormones:
– Anterior pituitary: composed of glandular
tissue and synthesizes six hormones
– Posterior pituitary: composed of neural
tissue and can be considered an extension
of the hypothalamus
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• Neurons in the hypothalamus synthesize the
hormones oxytocin and vasopressin, which
migrate down axons to the posterior pituitary
– Also known as antidiuretic hormones
• The hypothalamus secretes releasing
hormones
– Flow through the blood and stimulate the
anterior pituitary to release a number of
other hormones
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• The hypothalamus maintains a fairly constant
circulating level of hormones through a
negative-feedback system
– Example: TSH-releasing hormone
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May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
The Sequence of Chemical Events at
the Synapse (cont’d.)
• Neurotransmitters released into the synapse
do not remain and are subject to either
inactivation or reuptake
• Reuptake refers to when the presynaptic
neuron takes up most of the neurotransmitter
molecules intact and reuses them
• Transporters are special membrane proteins
that facilitate reuptake
– Example: serotonin is taken back up into
the presynaptic terminal
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• Examples of inactivation and reuptake
include:
– Acetylcholine is broken down by
acetylcholinesterase into acetate and
choline
• Excess dopamine is converted into inactive
chemicals:
– COMT: enzymes that convert the excess
into inactive chemicals
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• Negative feedback (for inhibiting further
release of neurotransmitters) in the brain is
accomplished in two ways:
– Autoreceptors: receptors that detect the
amount of transmitter released and inhibit
further synthesis and release
– Postsynaptic neurons: respond to
stimulation by releasing chemicals that
travel back to the presynaptic terminal
where they inhibit further release
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The Sequence of Chemical Events at
the Synapse (cont’d.)
• A few special-purpose synapses operate
electrically
• Faster than all chemical transmissions
• Needed when exact synchrony (e.g., rhythmic
breathing) between two cells is important
• Gap junction: the direct contact of the
membrane of one neuron with the membrane
of another
• Depolarization occurs in both cells, resulting
in the two neurons acting as if they were one
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© Argosy Publishing, Inc.
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Synapses, Drugs, and Addiction
• Drugs work by mimicking our own
neurochemistry
– Example: receptors in the brain respond to
LSD and cocaine
• Drugs alter various stages of synaptic
processing
– Antagonist: a drug that blocks a
neurotransmitter
– Agonist: a drug that increases a
neurotransmitter’s effects
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© Argosy
Publishing, Inc.
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A Survey of Abused Drugs
• Addictive substances affect dopamine and
norepinephrine synapses
• Olds and Milner (1954) placed rats in a
Skinner box that allowed self-stimulation of
the brain by the pressing of a lever
• Rats sometimes pressed the lever 2,000
times per hour to stimulate the release of
dopamine in the nucleus accumbens (having
role in processing of reward, motivation,
reinforcement learning)
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Photo credit: Omikron/Photo Researchers, Inc.
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs
• Other behaviors that release dopamine
include sexual excitement, gambling, and
video games
• People with major depression show less than
normal response in the nucleus accumbens.
They show little motivation and report getting
little joy out of life
• Like sex and food, addictive drugs strongly
activate the nucleus accumbens by releasing
dopamine or norepinephrine
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Berridge and Robinson (1998) suggest an
important distinction be made between
“liking” and “wanting” behaviors
• Small parts of the nucleus accumbens
respond to pleasure (liking)
• Larger parts respond to motivation (wanting)
• People addicted to drugs are highly motivated
to get them even if they no longer provide
pleasure
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Drugs are categorized according to their
predominant action or effect upon behavior
• Stimulant drugs increase excitement,
alertness, motor activity, and elevate mood
– Examples: amphetamines, cocaine,
methylphenidate (Ritalin), MDMA
(Ecstasy), and nicotine
– Amphetamine and cocaine inhibit the
dopamine transporter, thus decrease
reuptake and enable prolonged effects
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Amphetamine and cocaine stimulate
dopamine synapses by increasing the release
of dopamine from the presynaptic terminal
• Methylphenidate (Ritalin) also blocks the
reuptake of dopamine but in a more gradual
and more controlled rate
– Often prescribed for people with ADD
– Research has found inconclusive results
on whether Ritalin use in childhood makes
one more likely to abuse drugs as an adult
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Nicotine is the active ingredient in tobacco. It
enhances reward.
– Stimulates one type of acetylcholine
receptor known as the nicotinic receptor
– Nicotinic receptors are abundant in the
nucleus accumbens and facilitate
dopamine release
– Repeated exposure to nicotine makes it
more rewarding, but it makes every other
stimulus less rewarding
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Opiate drugs are those that are derived from
(or similar to those derived from) the opium
poppy
– Opiates decrease sensitivity to pain and
increase relaxation by attaching to
endorphin receptors in the brain
– Examples: morphine, heroin, methadone.
• People used opiates for centuries without
knowing how the drugs affected the brain.
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• The brain produces peptides called
endorphins (for inhibiting pain signals)
– Endorphin synapses may contribute to
certain kinds of reinforcement by inhibiting
the release of GABA indirectly
• Inhibiting GABA indirectly increases
dopamine (GABA inhibits dopamine)
– Endorphins also have reinforcing effects
independent of dopamine
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Tetrahydocannabinol (THC) is the active
ingredient in marijuana
• Psychological effects of marijuana include an
intensification of sensory experience and an
illusion that time has slowed down
– THC attaches to cannabinoid receptors
throughout the brain
• When certain neurons are depolarized, they
release anandamide or 2-AG as retrograde
transmitters that travel back to the incoming
axons and inhibit further release
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Anandamide and 2-AG tell the presynaptic cell,
“The postsynaptic cell got your message. You
don’t need to send it again.”
• The cannabinoids in marijuana attach to these
same presynaptic receptors, again telling them,
“The cell got your message. Stop sending it.”
• The presynaptic cell, unaware that it hadn’t sent
any message at all, stops sending.
• The chemicals in marijuana decrease both
excitatory and inhibitory messages from many
neurons
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Hallucinogenic drugs cause distorted
perception
– Many hallucinogenic drugs resemble
serotonin in their molecular shape
– Hallucinogenic drugs stimulate serotonin
type 2A receptors (5-HT2A) at inappropriate
times or for longer duration than usual thus
causing their subjective effect
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
• Types of hallucinogens:
– Lysergic acid diethylamide (LSD)
– Methylenedioxymethamphetamine (MDMA
or “ecstasy”): a stimulant at small dosages
but a hallucinogen at larger dosages
– Indication that long-term use of
hallucinogenic drugs is associated with
impaired memory and learning, and loss of
serotonin receptors
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
A Survey of Abused Drugs (cont’d.)
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Alcohol and Alcoholism
• Alcohol is a drug that has a long historical
use and is used widely throughout the world
– In moderate amounts, alcohol is
associated with relaxation
– In greater amounts it impairs judgment and
damages the liver and other organs, and
ultimately can ruin lives
– Alcoholism/alcohol dependence is the
habitual use of alcohol despite medical or
social harm
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Alcohol and Alcoholism (cont’d.)
• Alcohol has a number of diverse physiological
effects, including:
– Enhanced response by the GABAA
receptor (the brain’s main inhibitory site)
– Blockage of glutamate receptors (the
brain’s main excitatory site)
– Both the GABA and the glutamate effect
lead to a decrease in brain activity.
– Increased dopamine activity
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Alcohol and Alcoholism (cont’d.)
• Strong influence of genetics on alcoholism
– The genetic basis for early-onset
alcoholism is stronger than for later-onset,
especially in men
• Researchers distinguish between two types
of alcoholism
– Type I/Type A
– Type II/Type B
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Alcohol and Alcoholism (cont’d.)
• Type I/Type A characteristics include:
– Later onset (usually after 25)
– Gradual onset
– Fewer genetic relatives with alcoholism
– Equal quantity between men and women
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Alcohol and Alcoholism (cont’d.)
• Type II/Type B characteristics include:
– Earlier onset (usually before 25)
– More rapid onset
– More genetic relatives with alcoholism
– Men outnumber women
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Alcohol and Alcoholism (cont’d.)
• Genes influence the likelihood of alcoholism in
many ways, such as:
– Long form type 4 receptor are more sensitive and
need more alcohol to provide reinforcement
– More active COMT (an enzyme that breaks down
dopamine ) decreases reinforcement and is
linked to impulsivity (no forethought, reflection,
or consideration of the consequences). They
tend to choose immediate rewards instead of
bigger rewards later.
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Alcohol and Alcoholism (cont’d.)
• Prenatal environment also contributes to the
risk for alcoholism.
– A mother who drinks alcohol during
pregnancy increases the probability that
her child will develop alcoholism later,
• Research on sons of alcoholic fathers shows:
– Less average intoxication after one drink
– Stress decreases more than for the
average person
– Smaller than normal amygdala
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Alcohol and Alcoholism (cont’d.)
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Addiction
• As the addiction progresses, the pleasures become
weaker while the costs and risks increase. Users raise
the amount to greater levels.
• Body reacts strongly when the drug is absent. The
effects of drug cessation are called withdrawal.
• Various factors contribute to continued substance
abuse:
– Tolerance (decrease enjoyable effects) develops
– Cravings (abnormal desire) in response to cues
– Brain reorganization (in nucleus accumbens and
prefrontal cortex, change in response to rewards)
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Medications to Combat Substance
Abuse
• Medications used to combat alcoholism
include:
– Antabuse (Disulfiram plus alcohol produce
vomiting, chest pain, sweating, etc.)
– Revia (blocks opiate receptors and thereby
decreases the pleasure from alcohol)
– Many do not respond to other treatments
so medications have been used to reduce
cravings
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Medications to Combat Substance
Abuse (cont’d.)
• After alcohol consumption, enzymes in the
liver metabolize it into a poisonous substance
called acetaldehyde
• Acetaldehyde is converted into acetic acid, a
chemical that the body can use as a source of
energy. Antabuse (disulfiram) inhibits the
enzyme responsible for this process.
• Accumulation of acetaldehyde results in
sickness
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Medications to Combat Substance
Abuse (cont’d.)
• Most studies suggest that Antabuse has been
only moderately effective
– When effective, it supplements the
alcoholic’s own commitment to quit
– Daily routine of pill ingestion may reaffirm
commitment not to drink
– Many quit taking the pill and continue to
drink
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.
Medications to Combat Substance
Abuse (cont’d.)
• Methadone is an opiate similar to heroin and
morphine but is absorbed and metabolized
slowly
– Perceived to be less harmful than other
drugs
• Assumed to satisfy cravings associated
with previous drug use
• Levomethadyl acetate (LAAM) is similar to
morphine but can be taken three times a
week rather than daily
© 2013 Cengage Learning. All Rights Reserved. This edition is intended for use outside of the U.S. only, with content that may be different from the U.S. Edition.
May not be scanned, copied, duplicated, or posted to a publicly accessible website, in whole or in part.