Transcript `synapse`.

Synapses and Drugs
The Importance Of Synapses
► In
order to understand how drugs
work on the brain, we must first have
some understanding of how the brain
is constructed.
The basic unit: Neurons
► The
brain is a very complicated
collection of cells known as neurons or
(more informally) nerves.
► Neurons
receive
information
through branchlike structures
called dendrites.
As neurons grow,
their dendrites
reach out and
make contact
with the axons of
adjacent
neurons.
► There
is no physical contact between
the axon terminal of one neuron, and
the dendrites of another. Rather,
between the axon and the dendrites is
a space or gap, which is called the
'synapse'.
*Review the Synapse
► What
is a synapse?
► A synapse is the “gap” between the
axon of one nerve and the dendrite of
the next one.
► The average neuron has 1,000
synapses with other neurons.
Synaptic Transmission
► When
the action potential signal reaches the
terminal, the vesicles containing
neurotransmitters (NT) moves to the end and
the NT are released into the synapse.
► The NT floats across the synapse and connects
in lock-and-key fashion with protein
'receptors' embedded in the dendrites of the
receiving neurons.
► It is the presence of the NT 'keys' opening the
receptor 'locks' on the surface of the
dendrites of the post-synaptic neurons (and
not any electrical signal that jumps the
synapse) that excites or inhibits the postsynaptic neurons into activating or not.
Figure 48.12 A chemical synapse
*In more detail…
1.
2.
3.
Impulse from the 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
(continued)
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
“Re-uptake”
► After
a short while in the synapse, the
neurotransmitters that have been
released are recalled back into the
axon terminal in a process called 'reuptake' so that they are available
should the neuron need to fire again.
The Neurotransmitters
► There
are many different chemicals in
the brain that function as
neurotransmitters, but a small handful
do most of the work.
Acetylcholine
Serotonin
EPI
Endorphins
GABA
Neurotransmitters
► 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
► GABA
– Inhibitory - helps induce
relaxation and sleep. It balances the
brain by inhibiting over-excitation.
(Marijuana, depressant drugs)
► Glutamate
– Excitatory -is a major
excitatory neurotransmitter that is
associated with learning and memory.
► Dopamine
- Excitatory - involved in
controlling movement and posture. It also
modulates mood and plays a central role
in positive reinforcement and dependency.
(cocain, PCP, Heroin, opiates, marijuana,
amphetamines).
► 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. (alcohol,
hallucinogens, marijuana, stimulants).
► 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)
 (opiates, depressants)
Drugs Interfere with
Neurotransmission
►
Drugs can affect synapses at a
variety of sites and in a variety of
ways (agonize or antagonize),
including:
1. Increasing number of impulses
2. Release NT from vesicles with or without
impulses
3. Block reuptake or block receptors
4. Produce more or less NT
5. Prevent vesicles from releasing NT
►Most
of the drugs that get
abused are agonists
(enhancers) of various
neurotransmitters - they
work to enhance the natural
effect of neurotransmitters.
Three Drugs (of many) which
affect Neurotransmission
Methamphetamine
Nicotine
seattlepi.nwsource.com/ methamphetamines/
Alcohol
science.howstuffworks.com/ alcohol.htm