The provided code models the dynamics of NMDA (N-methyl-D-aspartate) receptors, which are a type of ionotropic glutamate receptor in the central nervous system critical for synaptic plasticity and transmission. Here's a summary of the biological aspects relevant to the code: ### Biological Components 1. **NMDA Receptors**: - NMDA receptors are ligand-gated ion channels that, upon binding of the neurotransmitter glutamate, allow the flow of cations, notably calcium (Ca²⁺), along with sodium (Na⁺) and potassium (K⁺). - The function of NMDA receptors is modulated by the presence of extracellular magnesium (Mg²⁺), which blocks the channel pore at resting membrane potentials. 2. **Magnesium Block**: - The code includes a parameter `mg`, representing external magnesium concentration. This reflects the physiological condition where Mg²⁺ blocks the NMDA receptor channels at resting potentials. The function `B` modulates synaptic conductance based on the voltage-dependent magnesium block, as described by a sigmoidal function. - When the neuron gets depolarized, the magnesium block is relieved, allowing ion flow through the receptor channel. 3. **Kinetics of Receptor Dynamics**: - Parameters such as `Alpha` (forward binding rate) and `Beta` (backward unbinding rate) help define the kinetics of glutamate binding and unbinding to the receptor. - These parameters reflect the dynamic opening and closing of the channel in response to synaptic events. 4. **Conductance and Current Calculation**: - The code calculates synaptic conductance `g` and the resulting synaptic current `i`. The current `i` is the product of the conductance and the driving force (the difference between the membrane potential `v` and the reversal potential `Erev`). 5. **Reversal Potential (`Erev`)**: - `Erev` represents the reversal potential of the NMDA receptor. Typically, it is close to 0 mV as the receptor is permeable to both Na⁺ and Ca²⁺, influencing excitatory postsynaptic potentials. 6. **Synaptic Transmission and Plasticity**: - NMDA receptors play a critical role in synaptic transmission and plasticity, particularly long-term potentiation (LTP), by allowing calcium influx, which acts as a second messenger in intracellular signaling pathways that modulate synaptic strength. Overall, the code captures the essential biophysical properties of NMDA receptors, focusing on their voltage-dependent magnesium block and the dual kinetics of receptor binding and unbinding. These properties enable the accurate simulation of NMDA receptor contributions to synaptic transmission and plasticity in computational modeling of neuronal networks.