Da far capire le integrazioni spaziali e temporali, l'allostati, il metabolismo, la modulazione.
Infatti l'espressione G. non e' come un programma tradizionale che puo' essere letto e capito, essendo i comportamenti omomorfi rispetto al codice. In un'espressione G. i comportamenti sono locali in tempo e spazio (contestualizzazione). Non essendoci un flusso programmatico, il commento ai comportamenti locali, non e' sufficienti a spiegare i comportamenti che sara' possibile verificare in diversi ambiti. C'e' quindi bisogno di esprimere i flussi e le chiusure che in diversi ambiti abbiamo voluto esprimere, tramite espressioni locali.
This document outlines the **Adaptive Engine Model** of the neuron, organized into four conceptual pillars. This framework describes a system that is not a static processor, but a living entity that balances high-speed communication with long-term survival and physical transformation.
### Pillar 1: The Electrical Pillar (The Execution Layer)
* **Function & Reason:** High-speed communication. This pillar allows the neuron to process information and "speak" to its neighbors in real-time. It is the engine’s "output."
### Pillar 2: The Metabolic Pillar (The Constraint Layer)
* **Function & Reason:** Sustainability and Gradient Maintenance. This pillar provides the energy required for all other behaviors. It sets the "Hard Limit" on how much work the neuron can do.
* **Timescale:** **Seconds to Minutes.**
* **Behaviors:** Active transport of ions, ATP production, and "Metabolic Silencing" (shutting down to prevent death when energy is low).
* **Elements Involved:**
* **Molecules:** ATP, Glucose, Oxygen.
* **Hardware:** Na/K-ATPase Pump (the "Battery Recharger"), Mitochondria.
* **Constraint:** The $Na^+/K^+$ ratio.
### Pillar 3: The Calcium Pillar (The Logic / Information Keeper)
* **Function & Reason:** Adaptation and Translation. This pillar acts as the "sensor" that monitors electrical activity and translates it into chemical signals. It keeps the "history" of the cell's workload.
* **Timescale:** **Minutes to Hours.**
* **Behaviors:** **Homeostatic Scaling** (tuning the master volume), Synaptic Plasticity (LTP/LTD), and Gain Control.
* **Software:** Calmodulin, CaMKIV (signaling proteins that "count" the calcium).
### Pillar 4: The Structural Pillar (The Renovation Layer)
* **Function & Reason:** Physical Transformation. This pillar is the actual rebuilding of the "factory" to change the neuron's fundamental capabilities. It is the physical manifestation of long-term memory and health.
* **Timescale:** **Days to Weeks.**
* **Behaviors:** **Axon Initial Segment (AIS) translocation** (moving the trigger zone), dendritic branch growth/pruning, and changes in total channel/receptor count via gene expression.
* **Elements Involved:**
* **Structural Proteins:** Actin, Microtubules, Ankyrin-G (the "anchor").
A system built on these four pillars is fundamentally different from a traditional computer. It achieves four "super-powers":
1.**Autonomous Homeostasis:** The neuron doesn't need a central controller. By using **Calcium** to monitor **Electricity**, it can independently adjust its own **Structure** to ensure it never exceeds its **Metabolic** budget.
2.**Context-Aware Information Processing:** The neuron is not a static logic gate. Its response to an input depends on its history. If it has been over-worked, it "wisely" raises its threshold to filter out noise and save energy.
3.**Resilience and Self-Repair:** Because it can physically renovate itself (Pillar 4), it can survive injuries, recover from metabolic exhaustion, and adapt to the loss of neighboring neurons.
4.**Optimal Efficiency:** It maximizes "Information per Joule." By tuning its electrical properties to its metabolic constraints, the neuron ensures that every spike is meaningful and every ATP molecule is well-spent.
**In conclusion, this entity is an "Adaptive Engine"—a machine that is constantly rewriting its own hardware while the power is still on, perfectly balancing the demands of communication with the strict laws of thermodynamics.**
* **Action Potential Arrival (`V_pre`):** When a spike occurs, the membrane potential (`V_pre_state`) jumps to a peak and decays based on `tau_V_pre`. This profile determines the duration of ion channel opening.
* **Calcium Influx (`VGCC`):** Voltage-Gated Calcium Channels open based on `V_pre_state`. The flow is regulated by three "brakes": **eCB** (retrograde), **CDI** (inactivation), and **mGluR** (autoreceptor).
* **Intracellular Buffering:** Free calcium (`Ca_micro`) is immediately captured by buffers (`B_free`). As activity increases and buffers saturate, the effective calcium concentration rises faster (**Metabolic Cascade 4**).
* **Vesicle Release (NT):** Neurotransmitter release is **deterministic** and follows a Hill equation (simulating Synaptotagmin-1 cooperativity). It is limited by the number of vesicles in the Prontly Releasable Pool (`N_RRP`) and suppressed by high existing levels of NT in the cleft.
* **Vesicle Recycling:** Vesicles move from the Reserve Pool (`N_RP`) to the `N_RRP` at a rate determined by the calcium trace (`Tr_Ca`). Fast recruitment occurs during high activity; slow recruitment occurs at rest.
* **Calcium-Dependent Inactivation (CDI):** Local calcium entering through channels causes them to close (`CDI_factor`). If calcium clearance fails due to low ATP, the CDI "locks" the synapse into a silent state to prevent damage.
* **AMPA Activation:** Released NT opens AMPA receptors, allowing **Na+** influx. This generates the local excitatory post-synaptic potential (EPSP).
* **Receptor Desensitization:** Continuous exposure to NT reduces the sensitivity of the receptors (`Desensitization_level`), mimicking the presynaptic CDI behavior to prevent over-stimulation.
* **NMDA Coincidence Detection:** NMDA channels open only if **NT is present** AND the **membrane is depolarized** (removing the Mg2+ block). Depolarization is achieved via local AMPA drive plus the back-propagating action potential (**bAP**) from the soma.
* **eCB Synthesis:** When postsynaptic calcium (`Ca_post`) crosses a specific threshold, **Endocannabinoids** are synthesized and sent back to the presynapse to suppress further NT release.
* **EPSP Summation:** The dendritic branch (`DB`) acts as a passive integrator. It collects `receptor_conductance` from all active spines and sums them into `V_dend`.
* **Passive Decay:** `V_dend` decays over time according to `tau_dend`, determining the temporal window in which multiple inputs can summate to trigger a somatic spike.
* **bAP Distribution:** When the soma fires, a **back-propagating Action Potential** (`V_bAP`) is broadcasted instantly through the dendrite to all spines to enable NMDA coincidence detection.
* **Leaky Integration:** The soma integrates the signal from the dendrite (`V_dend`) scaled by `soma_weight`. It acts as a leaky integrator with a time constant of `tau_soma`.
* **Action Potential (AP) Generation:** If `V_soma` crosses the threshold, a multi-phase AP is triggered:
2.**Falling Phase:** Simulated K+ channel opening (drops to `V_AHP`).
3.**AHP Phase:** Recovery from hyperpolarization back to rest.
* **Refractory Periods:** After firing, the soma enters an **Absolute Refractory Period** (cannot fire) followed by a **Relative Refractory Period** (threshold is temporarily much higher).
* **Neurotransmitter Clearance:** The astrocyte actively removes NT from the synaptic cleft, governed by the `tau_NT_decay` and metabolic cycles.
* **Glutamine Shuttle:** Cleared NT is converted and recycled back to the presynaptic Reserve Pool (`RP`) with a specific `conversion_efficiency`.
* **IP3 Signaling & Calcium Wave:** Accumulated NT triggers **IP3** production in the astrocyte. If it crosses a threshold, an **astrocytic calcium wave** is triggered.
* **Metabolic Support:** The calcium wave provides a "boost" to the `conversion_efficiency`, helping the synapse recover vesicles faster during high demand.
* **ATP Consumption:** Every Action Potential (Pre and Post) and every calcium pumping action (`PMCA`, `SERCA`) drains a shared **Glucose/ATP** budget.
* **Pump Scaling:** The speed of ion pumps is determined by a Hill function of available `ATP_level`. Low energy leads to **Pump Failure**.
* **Metabolic Silencing:** A 6-stage cascade where high firing leads to ATP depletion, which causes pump failure, leading to residual calcium, which triggers CDI, finally **silencing the synapse** to protect against excitotoxicity.
