Transcript 10Synapses_and_Drugs 13

Synapses and Drugs
Review the Synapse
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What is a synapse?
A synapse is the “gap” between the axon
of one neuron (typo on your page –
change to neuron) and the dendrite of the
next one.
The average neuron has 1,000 synapses
with other neurons.
What does a synapse look like?
Murthy_HHMI_teachers_2005_sub.ppt
Figure 48.12 A chemical synapse
Key to Previous Diagram
1.
2.
3.
Impulse from action potential opens
ion channels for Ca++
The increased Ca++ concentration in the
axon terminal initiates the release of the
neurotransmitter (NT)
NT is released from its vesicle and
crosses the “gap” or synaptic cleft and
attaches to a protein receptor on the
dendrite
Key to Diagram (cont.)
4.
5.
Interaction of NT and protein receptor
open post-synaptic membrane ion
channel for Na+
After transmission the NT is either
degraded by an enzyme or taken back
into the pre-synaptic membrane by a
transporter or reuptake pump
Neurotransmitters
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There are dozens of different
neurotransmitters (NT) in the neurons of
the body.
NTs can be either excitatory, which causes
the next neuron to fire, or inhibitory,
which stops the next neuron from firing.
Each neuron generally synthesizes and
releases a single type of
neurotransmitter
Major Neurotransmitters in the
Body
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GABA – Inhibitory - helps induce
relaxation and sleep. It balances the brain
by inhibiting over-excitation.
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Glutamate – Excitatory -is a major
excitatory neurotransmitter that is
associated with learning and memory.
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Dopamine - Excitatory - involved in
controlling movement and posture. It also
modulates mood and plays a central role
in positive reinforcement and
dependency.
Serotonin –Excitatory - contributes to
various functions, such as regulating body
temperature, sleep, mood, appetite, and
pain. Low serotonin levels have been
linked to depression, suicide, impulsive
behavior, and aggressiveness.
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Endorphins – Excitatory and inhibitory
- interact with the opiate receptors in
the brain to reduce our perception of
pain. Secretion of endorphins leads to
feelings of euphoria, modulation of
appetite, release of sex hormones, and
enhancement of the immune response.
(runner’s high)
Drugs Interfere with
Neurotransmission
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Drugs can affect synapses at a variety of
sites and in a variety of ways, including:
1.
2.
Increasing number of impulses (by
increasing NT release) – alcohol, nicotine &
opiates
Release NT from vesicles with or without
impulses (amphetamines and
methamphetamines)
3.
4.
Block reuptake (cocaine) or block receptors
(lsd or caffeine)
Release more NT in response to an impulse
(nicotine) (change in your notes)
5. Blocks receptor with an NT imitator(LSD and
caffeine) (change in notes)
Three Drugs (of many) which
affect Neurotransmission
Methamphetamine
Nicotine
seattlepi.nwsource.com/ methamphetamines/
Alcohol
science.howstuffworks.com/ alcohol.htm
Barbiturates (aka
sleeping pills)
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These drugs block
the sodium ion
channels. Because
sodium ions cannot
flow in, action
potentials cannot be
produced. So it
slows down or stops
nerve impulses
Nicotine
Binds to specific receptors on the presynaptic
neuron and excites the neuron so that it fires
more action potentials (electrical signals) that
move toward the synapse, causing more
dopamine release.
The receptors for nicotine are called “nicotine
receptors” because they can bind with
nicotine,
but normally they bind with a natural
neurotransmitter, acetylcholine. Your body
regulates the amounts of acetylcholine so
overstimulation does not happen.
But your body cannot regulate the amount of
nicotine you consume, so overstimulation
results. Nicotine and acetylcholine have very
similar 3-D structures.
Methamphetamine alters dopamine neurotransmission in two ways.
1 - Methamphetamine
enters the neuron by
passing directly through
nerve cell membranes.
It is carried to the nerve
cell terminals by
transporter molecules
that normally carry
dopamine or
norepinephrine.
In the nerve terminal,
2 - Methamphetamine also
methamphetamine
blocks the dopamine
enters the dopamine- or transporter from pumping
norepinephrinedopamine back into the
containing vesicles and
transmitting neuron.
causes the release of
neurotransmitter.
Cocaine
When it enters the brain,
it blocks the dopamine
transporter from
pumping dopamine
back into the
transmitting neuron,
flooding the synapse
with dopamine.
This intensifies and
prolongs the
stimulation of receiving
neurons in the brain's
pleasure circuits,
causing a cocaine
"high."
Cocaine and Addiction
Addiction
The brain will reduce the number of receptors
in response to the high levels of
neurotransmitters. Now the normal amounts
of natural neutrotransmitters will not trigger
as great of a response as before.
OR
 The brain will lower the level of
neurotransmitters released, so even if the
nerve is stimulated, less neurotransmitters
are released, so all nerve responses are
lessened.
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Resources
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http://www.pbs.org/
wnet/closetohome/ho
me.html
http://www.biologym
ad.com/NervousSyste
m/synapses.htm#dru
gs
http://users.rcn.com/j
kimball.ma.ultranet/Bi
ologyPages/S/Synaps
es.html
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http://science.educati
on.nih.gov/Customers
.nsf/HSBrain?OpenFor
m
Biology, Campbell and
Reece, 6th Edition,
Benjamin Cummings,
San Francisco, 2002
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More Related Websites to
Explore
http://faculty.washington.edu/chudler/neurok.ht
ml
http://www.teachersdomain.org/
http://science.nhmccd.edu/biol/ap1int.htm
http://www.hhmi.org/
http://www.med.harvard.edu/AANLIB/home.htm
l
http://www.med.harvard.edu/publications/On_T
he_Brain/