The code provided is part of a computational model for a neuronal cell, specifically inspired by the Pinsky-Rinzel model, which is a simplified version of a complex multi-compartment model of hippocampal CA3 pyramidal neurons. The focus here is on capturing the essential electrophysiological properties of the neurons. ### Biological Basis 1. **Membrane Capacitance (`Cm`)**: - Represented as 3 µF/cm², this value characterizes the cell membrane's ability to store charge. In biological terms, it reflects the lipid bilayer's capacity to separate charge, essential for action potential propagation. 2. **Ionic Conductances**: - **`gNa`, `gKDR`, `gKC`, `gKAHP`, `gCa`**: These parameters represent conductances of sodium (Na⁺), delayed rectifier potassium (K⁺), calcium-activated potassium (K⁺, divided into `KC` for rapid and `KAHP` for slow), and calcium (Ca²⁺) channels. Each of these conductances plays a crucial role in shaping the action potential and regulating neuronal excitability: - **`gNa` (Sodium)**: Essential for the depolarization phase of the action potential. - **`gKDR` (Potassium, Delayed Rectifier)**: Contributes to repolarization and helps return the membrane potential to baseline after an action potential. - **`gKC` and `gKAHP`**: Both are involved in action potential repolarization in association with Ca²⁺ dynamics. `gKAHP` is particularly crucial for afterhyperpolarization, affecting neuronal firing patterns. - **`gCa` (Calcium)**: Often regulates both neurotransmitter release and other conductance properties through intracellular signaling. 3. **Reversal Potentials (`ENa`, `Ek`, `ECa`, `EL`)**: - These potentials determine the direction of ion flow through respective channels, critical for generating and shaping action potentials: - **`ENa` (Sodium Reversal Potential)**: Set at 120 mV relative to a reference potential, reflecting the high sodium gradient across the neuronal membrane. - **`Ek` (Potassium Reversal Potential)**: Given as an input parameter reflecting the dynamic range of available K⁺. - **`ECa`, `EL`**: Relate to calcium and leak channels respectively, influencing intracellular calcium levels and maintaining resting membrane potential. 4. **Synaptic and Compartmental Parameters**: - **`gc` (Coupling Conductance)**: Represents the conductance between connected compartments of the neuron, modeling inter-compartmental communication. - **`p` (Compartment Ratio)**: The fraction of the neuronal area allocated to the soma, a parameter significant in compartmental models to represent spatial distinctions across the neuron. - **`Vsyn` (Synaptic Reversal Potential)**: Indicative of synaptic inputs, set at 60 mV, which can impact neuronal firing patterns via excitatory post-synaptic potentials (EPSPs). 5. **Injected Current (`Isinj`, `Idinj`)**: - Represents external currents injected into the soma and dendrites, respectively. This is often used to simulate naturally occurring synaptic input or experimental current injection. 6. **Units**: - Clear annotations regarding units ensure consistent interpretation and scaling, crucial in translating biological parameters into a computational framework. Overall, this model encapsulates essential features of neuronal dynamics such as ion conductance and membrane properties. By tuning these parameters, researchers can simulate the diverse electrophysiological behaviors observed in hippocampal pyramidal neurons, including action potential firing and synaptic integration.