Update presynapse.md

elements/neuron/presynapse.md

@@ -4,7 +4,6 @@ include_toc: true
 
 // presynapse.md
 
-# PRESYNAPSE
 
 Expansions and modulations:
   - is expanded and developed by: [AXON](axon.md)
@@ -12,6 +11,26 @@ Expansions and modulations:
   - expands and tunes: [PRE_VGG](pre_vgcc.md)
   - develops _Ca2, _Rrp
 
+  Introduction: 
+  The presynaptic bouton releases neurotransmitter and gathers evidence about whether that release was worth strengthening and worth sustaining. Its behavior unfolds across two DAY contexts and the NIGHT scope.
+
+  During DAY, during AP — the bouton releases neurotransmitter. The amount released depends on:
+  
+  - residual calcium from recent spikes (the fast trace), which sets the release drive;
+  - the two retrograde messages from the postsynapse — retro_eCB brakes the drive (the postsynapse is over-driven), retro_NO will later confirm that release reached a responsive target;
+  - the availability of both fuel and vesicles — release proceeds only if budget covers the cost and the readily-releasable pool is non-empty. These two shortfalls are read differently: a fuel shortfall on a succeeding release is evidence the bouton needs more endurance; an empty pool with fuel to spare is ordinary short-term depression.
+  
+  During DAY, during NOT_AP — the bouton consolidates and recovers. With no spike to release, it:
+  
+  - receives what arrived — latches the retrograde messages, refills its budget from astrocytic lactate and arrived axonal shipment (contested supply);
+  - maintains its traces — accumulates eligibility toward a tag, and stabilizes that tag if dopamine has arrived (the bridge toward strength);
+  - recovers its readily-releasable pool from the private reserve, between spikes (which is why high-frequency firing depletes faster than it recovers);
+  - lets its traces decay, closing the eligibility, endurance, and tagging windows.
+  
+  During NIGHT — the bouton's ceilings are rewritten. Acting on the evidence gathered across the day, NIGHT raises the bouton's structure (active-zone capacity) where a validated tag accumulated, and its budget capacity (mitochondrial endurance) where fuel repeatedly interrupted a succeeding release. Both draw on the same finite material and energy shipped down the axon, so the bouton's two kinds of growth compete — and whatever is not maintained drifts back down.
+
+# PRESYNAPSE
+
 ```Gen
 
 include: