The provided code is a computational model designed to simulate synaptic transmission mediated by NMDA receptors, crucial components of synaptic plasticity and neural communication in the brain. Here’s a breakdown of the biological aspects represented in the code: ### Synaptic Transmission - **Presynaptic and Postsynaptic Compartments**: - The model creates two neuronal compartments: `PRE` (presynaptic) and `POST` (postsynaptic). These compartments represent the two sides of a synapse where neurotransmitter release and reception occur. ### Presynaptic Mechanisms - **Transmitter Release**: - The presynaptic compartment (`PRE`) is set up to simulate action potential propagation, leading to neurotransmitter release. This is indicated by the insertion of a mechanism for transmitter release (`glurel`), simulating the release of glutamate. ### Postsynaptic Mechanisms - **NMDA Receptors**: - The code uses a kinetic model of NMDA receptors based on the work by Clements & Westbrook (1991). NMDA receptors are critical for synaptic transmission that involves calcium influx, which influences synaptic plasticity mechanisms such as long-term potentiation (LTP). - A specific NMDA receptor subtype (`NMDA5`) is instantiated and located at the `POST` compartment, with its activity modeled by a series of kinetic state transitions (i.e., binding, unbinding, desensitization, resensitization, opening, and closing). ### Biochemical Parameters - **Reversal Potential**: - `Erev_NMDA5` is set to 0 mV, representing the reversal potential for NMDA-mediated currents, which is the voltage at which no net current flows through the receptor channel. - **Magnesium Block**: - `mg_NMDA5` is set to zero, which in biological systems would simulate conditions without the typical magnesium block that NMDA receptors experience under resting membrane potentials. Magnesium normally blocks NMDA channels at hyperpolarized potentials, which is relieved upon depolarization. ### Kinetic Parameters - The various rate constants (`Rb_NMDA5`, `Ru_NMDA5`, `Rd_NMDA5`, `Rr_NMDA5`, `Ro_NMDA5`, `Rc_NMDA5`) define the transitions between different receptor states: - **Binding (`Rb_NMDA5`)** and **Unbinding (`Ru_NMDA5`)**: Represent the association and dissociation of glutamate to the receptor. - **Desensitization (`Rd_NMDA5`)** and **Resensitization (`Rr_NMDA5`)**: Describe the receptor becoming less responsive or returning to a responsive state. - **Opening (`Ro_NMDA5`)** and **Closing (`Rc_NMDA5`)**: Govern the transition of the channel between open and closed conformations. ### Maximum Conductance - `c.gmax` parameter sets the peak conductance of the NMDA channel, indicative of the maximum current that can flow through the receptor when fully open. ### Visualization - The code includes graphical outputs to visualize neurotransmitter concentration and NMDA receptor-mediated current over time, which helps in understanding the dynamics of synaptic transmission. Overall, this code simulates the detailed mechanisms by which NMDA receptors function during synaptic transmission, providing insights into the processes underlying synaptic integration and plasticity.