Dopamine (DA) neuron

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axons
Dendrites
terminals
Cell body (Soma)
Dopamine (DA) neuron
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axons
Dendrites
terminals
Cell body (Soma)
Dopamine (DA) neuron
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Chemical signals Generate EPSPs Or IPSPs
axons
terminals
Cell body (Soma)
Dopamine (DA) neuron
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If excitation caused By EPSPs is great Enough to
cross the threshold, An Action Potenial is
generated.
axons
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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Action Potentials travel along the axon
axons
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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AXON
Towards terminals
Towards soma
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Excitation above the threshold Opens
Voltage-gated Na channels
Na
AXON
Towards terminals
Towards soma
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Na ions rush into cell, causing Action Potential
(ascending limb)
Na
Na Na Na
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
K moves out To restore resting Potential (i.e.,
Descending limb)
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potential is propagated down The Axon
K
Na
Na Na Na
K
AXON
Towards terminals
Towards soma
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Action Potentials travel along the axon
axons
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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axons
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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axons
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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axons
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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axons
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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causing neurotransmitter release from the
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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causing neurotransmitter release from the
terminals
Cell body (point of origin)
Dopamine (DA) neuron
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Stages of Synaptic Transmission

• SYNTHESIS- neurotransmitter is produced by
  enzymes
• STORAGE- stored in vesicles
• RELEASE- released into the synapse
• POSTSYNAPTIC ACTION- acts on postsynaptic
  receptors
• INACTIVATION- broken down by enzymes or taken up
  into cells

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SYNAPSE Point of functional connection
DA terminal

• Transmitter is
• synthesized from a
• precursor molecule by
• enzymes in the
• presynaptic cell

Synaptic cleft
Postsynaptic cell
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SYNAPSE Point of functional connection
DA terminal
2. Transmitter is stored in presynaptic vesicles

Synaptic cleft
Postsynaptic cell
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Electrical impulse action potential
DA terminal

Synaptic cleft
Postsynaptic cell
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DA terminal
Synaptic cleft
Postsynaptic cell
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DA terminal
Ca
3. Release. Action Potential opens voltage- Gated
Ca channels
Synaptic cleft
Postsynaptic cell
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DA terminal
Ca
Ca
Ca
Ca
3. Release. There is an influx of Ca into
the terminal
Synaptic cleft
Postsynaptic cell
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DA terminal
3. Ca influx promotes several processes
that lead the vesicles to go from a pre-release
state into a fusion with release sites on the
membrane. Transmitter is released
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Synaptic cleft
Postsynaptic cell
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DA terminal
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Transmitter diffuses across synaptic cleft
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Synaptic cleft
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Postsynaptic cell
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DA terminal
Transmitter diffuses across synaptic cleft
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Synaptic cleft
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Postsynaptic cell
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DA terminal
4. Postsynaptic Action. a) Transmitter binds to
postsynaptic receptors
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Synaptic cleft
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DA Receptor proteins
Postsynaptic cell
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DA terminal
4. Postsynaptic Action. b) Transmitter
binding induces intrinsic biological activity
(i.e. signal transduction effects)
in postsynaptic cell.
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Synaptic cleft
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Physiological and biochemical effects (EPSPs or
IPSPs)
Postsynaptic cell
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DA terminal
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• 5. Inactivation.
• Transmitter is transported back into presynaptic
  terminal
• by protein transporter (i.e.,
• uptake or reuptake).

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Synaptic cleft

Postsynaptic cell
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DA terminal
5. Inactivation. b) Transmitter is broken down
(i.e. metabolized) by enzymes.
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Synaptic cleft
.

Postsynaptic cell
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STUDIES OF THE BEHAVIORAL EFFECTS OF DRUGS

• DRUGS MODIFY THE PROCESS OF CHEMICAL TRANSMISSION
  IN THE NERVOUS SYSTEM
• Alter neurotransmitter synthesis
• Block storage of transmitter
• Stimulate or reduce release
• Stimulate or block receptors
• Block the enzymatic breakdown or uptake of
  transmitter