Synaptic Transmission Lesson 11 Synapses Signaling between neurons

Synaptic Transmission Lesson 11

Synapses Signaling between neurons l chemical l few electric n Chemical synapse types l axodendritic l axosomatic l axoaxonic l dendrodendritic ~ n

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

2. Synthesis l Enzymes & cofactors l Can be multiple steps ~ E

3. Storage In vesicles E

3. Storage In vesicles Terminal Button Dendritic Spine Synapse

4. Release AP Ca++ Synapse

4. Release diffusion Ca++

5. Activation l NT binds to receptor

Activation n NT binds to postsynaptic receptor l opens ion channel l EPSP l or IPSP ~

6. Termination n 4 Basic methods l Diffusion l Enzymatic degradation l Presynaptic reuptake uactive l transport Autoreceptors ~

6. Termination E A RU E

Autoreceptors On presynaptic terminal n Binds NT l same as postsynaptic receptors l different receptor subtype n Decreases NT release & synthesis l via 2 d messenger system ~ n

Termination Must have discrete signal n What if ion channels continually open? n Disrupts neural communication n Termination neuron repolarizes ~ n

Drug Interaction Terms Drug’s effect on synaptic transmission l Direct at postsynaptic receptor l Indirect at any other step n Agonist (AG) l mimics or NT effects n Antagonist (ANT) l blocks or ¯ NT effects ~ n