Chapter 31 Main Points

🔑 Key Definitions

          Exocytosis: Process where synaptic vesicles fuse with membrane and release neurotransmitter into cleft

          Axonal Transport: Movement of materials along axon from soma to terminals (anterograde) or terminals to soma (retrograde)

          Second Messenger: Intracellular molecule (like cAMP) activated by receptor binding; amplifies signal

          Reuptake: Neurotransmitter deactivation method where presynaptic neuron reabsorbs NT from cleft

🧠 Five Steps of Synaptic Transmission

1. Synthesis: Neurotransmitter produced in cell body or terminal
2. Storage: NT packaged into synaptic vesicles
3. Release: Action potential triggers Ca2+ influx → vesicles fuse with membrane → exocytosis
4. Receptor Binding: NT crosses cleft and binds to postsynaptic receptors
5. Deactivation: NT removed from cleft by reuptake, enzymatic breakdown, or diffusion

📊 Receptor Mechanisms

Direct (Ionotropic): NT binds to receptor that IS an ion channel; fast response (milliseconds)
Indirect (Metabotropic): NT binds to G-protein coupled receptor; activates second messengers; slower but longer-lasting
cAMP (Cyclic AMP): Common second messenger; amplifies signal inside cell
Signal Amplification: One NT molecule can activate many second messengers

📊 NT Deactivation Methods

Reuptake: Transporter proteins pump NT back into presynaptic terminal (most common for monoamines)
Enzymatic Degradation: Enzymes in cleft break down NT (e.g., acetylcholinesterase for ACh)
Diffusion: NT drifts away from synapse

💡 Exam Tips

Remember 5 steps in order: Synthesis → Storage → Release → Binding → Deactivation
Ca2+ influx triggers exocytosis - calcium is the key trigger
Direct receptors = fast (ionotropic), Indirect = slow but amplified (metabotropic)
cAMP is classic example of second messenger
Drugs can affect ANY of the 5 steps (synthesis blockers, reuptake inhibitors, etc.)
Anterograde transport = away from soma, Retrograde = toward soma