axons
Dendrites
terminals
Cell body
(Soma)
Dopamine (DA) neuron
Most information
comes in here
axons
Dendrites
terminals
Cell body
(Soma)
Dopamine (DA) neuron
Chemical signals
Generate EPSPs
Or IPSPs
axons
terminals
Cell body
(Soma)
Dopamine (DA) neuron
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
Action Potentials
travel along the
axon
axons
terminals
Cell body
(point of origin)
Dopamine (DA) neuron
AXON
Towards
soma
Towards
terminals
Excitation above the threshold
Opens Voltage-gated Na+ channels
Na+
AXON
Towards
soma
Towards
terminals
Na+ ions rush into cell, causing
Action Potential (ascending limb)
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
K+ moves out
To restore resting
Potential (i.e.,
Descending limb)
Towards
soma
AXON
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potential is propagated down
The Axon
K+
K+
Na+
Na+ Na+
Na+
AXON
Towards
soma
Towards
terminals
Action Potentials
travel along the
axon
axons
terminals
Cell body
(point of origin)
Dopamine (DA) neuron
axons
terminals
Cell body
(point of origin)
Dopamine (DA) neuron
axons
terminals
Cell body
(point of origin)
Dopamine (DA) neuron
axons
terminals
Cell body
(point of origin)
Dopamine (DA) neuron
axons
terminals
Cell body
(point of origin)
Dopamine (DA) neuron
axons
. .. . .. .
..
.. ..
..
. . . .
. . .. . ..
. ..
.
Cell body
(point of origin)
causing
neurotransmitter
release from the
terminals
Dopamine (DA) neuron
. .
. .
.
.
.
..
..
.
. .
. .
. ..
. . .. . . . . .
.
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axons
Cell body
(point of origin)
causing
neurotransmitter
release from the
terminals
Dopamine (DA) neuron
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
SYNAPSE: Point of functional connection
DA terminal
Synaptic
cleft
1. Transmitter is
synthesized from a
precursor molecule by
enzymes in the
presynaptic cell
Postsynaptic cell
SYNAPSE: Point of functional connection
DA terminal
Synaptic
cleft
2. Transmitter is stored
in presynaptic vesicles
Postsynaptic cell
Electrical
DA
impulse
“action potential”
terminal
Synaptic
cleft
Postsynaptic cell
DA terminal
Synaptic
cleft
Postsynaptic cell
DA terminal
Synaptic
cleft
Ca++
3. Release. Action
Potential opens voltageGated Ca++ channels
Postsynaptic cell
DA terminal
Ca++
Ca++
Ca++
Synaptic
cleft
Ca++
3. Release. There is an
influx of Ca++ into the
terminal
Postsynaptic cell
DA terminal
Synaptic
cleft
....
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
Postsynaptic cell
DA terminal
Synaptic
cleft
.. ..
.... .
Transmitter
diffuses across
synaptic cleft
Postsynaptic cell
DA terminal
Synaptic
cleft
. .
.
.
. ..
.
.
Transmitter
diffuses across
synaptic cleft
Postsynaptic cell
.
DA terminal
Synaptic
cleft
. .
.
.
.
.
.
4. Postsynaptic Action.
a) Transmitter binds
to postsynaptic
receptors
.
DA Receptor proteins
Postsynaptic cell
.
DA terminal
Synaptic
cleft
..
.
4. Postsynaptic Action.
b) Transmitter binding
induces intrinsic biological
activity (i.e. signal
transduction effects) in
postsynaptic cell.
Physiological and biochemical
effects (EPSPs or IPSPs)
Postsynaptic cell
DA terminal
Synaptic
cleft
.
..
5. Inactivation.
a) Transmitter is
transported back into
presynaptic terminal
by protein transporter (i.e.,
uptake or “reuptake”).
Postsynaptic cell
DA terminal
Synaptic
cleft
.
.
5. Inactivation.
b) Transmitter is broken
down (i.e. “metabolized”)
by enzymes.
Postsynaptic cell
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