Synaptic Transmission Lesson 11 Synaptic Events Action Potential

Synaptic Transmission Lesson 11

Synaptic Events Action Potential reaches axon terminal n Chemical substance released l Neurotransmitter (NT) n Diffuses across synapse n Binds to receptor protein l EPSP or IPSP ~ n

Synaptic Transmission Model 1. 2. 3. 4. 5. 6. Precursor transport NT synthesis Storage Release Activation Termination ~

Presynaptic Axon Terminal Button Postsynaptic Membrane Dendritic Spine

1. Precursor Transport

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 Ca++

4. Release • via exocytosis • diffusion AP Ca++ Synapse

4. Release • via exocytosis • diffusion Ca++

Exocytosis: Membrane Fusion n Ca 2+ influx 2+ -Calmodulin l. Ca lsynapsin SNAPs lsoluble-NSF-attachment proteins l. Cell membrane SNAREs l. SNAP receptors l. Vesicle & cell membrane~

5. Activation l NT binds to receptor

Activation n NT binds to postsynaptic receptor l opens ion channel l EPSP u. Na+ l into cell or IPSP u. K+ out of cell ~

6. Termination l 4 basic methods

6. Termination l diffusion

6. Termination l Enzymatic degradation

6. Termination l Presynaptic reuptake uactive transport

6. Termination l autoreceptors A

Autoreceptors On presynaptic terminal n Binds NT l same as postsynaptic receptors l different receptor subtype n Decreases NT release & synthesis ~ n

Termination Must have discrete signal n What if ion channels continually open? l ions move toward equilibrium l membrane no longer polarized l no EPSPs or IPSPs n Disrupts neural communication n Termination neuron repolarizes ~ n

Axoaxonic Synapses Modulation of NT release n Presynaptic Facilitation l Increases NT release n Presynaptic Inhibition l decreases NT release n Via modulation of Em 2+ + - ~ l Ca , K , and Cl n