Download BN12 synaptic transmission

Synaptic
Transmission
Lesson 12
Synapses
Communication b/n neurons
 Electrical
 Electrotonic conduction
 Chemical
 Ligand / receptor ~

Electrical Synapses
Tight junctions
 Connexons
 Passive current
 & larger molecules (e.g., ATP)
 Synchronous activity
 Breathing
 Hormone release from
hypothalamus ~

Synaptic Events
Action Potential reaches axon terminal
 Chemical substance released
 Neurotransmitter (NT)
 Diffuses across synapse
 Binds to receptor protein
 EPSP or IPSP ~

Synaptic Transmission Model
1.
2.
3.
4.
5.
6.
Precursor transport
NT synthesis
Storage
Release
Activation
Termination ~
Presynaptic
Axon Terminal
Terminal
Button
Postsynaptic
Membrane
Dendritic
Spine
1. Precursor
Transport
2. Synthesis
Enzymes & cofactors ~
E
3. Storage
E
3. Storage
In vesicles
Terminal
Button
Dendritic
Spine
Synapse
4. Release
• via exocytosis
• diffusion
AP
Ca++
Synapse
Exocytosis: Membrane Fusion



Ca2+ influx
d
2 messenger
2+ -Calmodulin
Ca
SNAPs
soluble-NSFattachment proteins
SNAREs
SNAP receptors ~
5. Activation
 NT binds to receptor
Activation

NT binds to postsynaptic receptor
 opens ion channel
 EPSP
Na+

into cell
or IPSP
K+
out of cell ~
6. Termination

4 Basic methods
 Diffusion
 Enzymatic degradation
 Presynaptic reuptake
active

transport
Autoreceptors ~
6. Termination
 autoreceptors
A
Autoreceptors
On presynaptic terminal
 Binds NT
 same as postsynaptic receptors
 different receptor subtype
 Decreases NT release & synthesis ~

Termination
Must have discrete signal
 What if ion channels continually open?
 ions move toward equilibrium
 membrane no longer polarized
 no EPSPs or IPSPs
 Disrupts neural communication
 Termination ---> neuron repolarizes ~

Axoaxonic Synapses
Modulation of NT release
2+ influx
 *via  or  Ca
 Presynaptic Facilitation
 Increases NT release
 Presynaptic Inhibition
 decreases NT release
 Via modulation of Em
2+, K+, and Cl- ~
 Ca

Drug Interaction Terms
Drug’s effect on synaptic transmission
 Direct  at postsynaptic receptor
 Indirect  at any other step
 Agonist (AG)
 mimics or NT effects
 Antagonist (ANT)
 blocks or  NT effects ~
