The code provided is a computational model simulating the electrophysiological properties of neuronal dendrites, specifically those with tonically activated conductances. Below is an explanation of the biological basis of this model, focusing on the key aspects represented in the code. ### Biological Basis #### Neuronal Dendrites Dendrites are the branched extensions of neurons that receive synaptic inputs from other neurons. They play a crucial role in integrating synaptic inputs and determining the neuronal output. The structure and electrical properties of dendrites significantly influence how signals are processed within a neuron. #### Tonically Activated Conductances The model simulates the effect of tonically activated membrane conductances, which are ion channels that are consistently open or active. This tonic activity affects the resting potential and overall excitability of the dendrites. #### Key Ions and Conductances 1. **Sodium (Na⁺) Channels**: These are represented by the `gna_hh1` in the code, following the Hodgkin-Huxley model, which is pivotal in the generation and propagation of action potentials. 2. **Potassium (K⁺) Channels**: Represented by `gk_hh1`, these channels are critical for repolarization of the neuron and maintaining the resting membrane potential. 3. **Leak Conductance**: The `gl_hh1` and `gs_PasS` parameters model passive membrane properties, including the movement of ions through non-gated (leak) channels, which contribute to the resting membrane potential. #### Membrane Potential and Conductance - The membrane potential (`v`) is vital for neuronal signaling and is influenced by the combination of various ion channels. - The equilibrium potential (`Eq`) for each section of the dendrite is computed, integrating contributions from all active conductances, influencing how each segment responds to inputs. #### Graphics for Analysis The code includes procedures to generate graphical representations of various properties along the dendrite: - **Voltage Distribution** (`MakeVRGraph`): Displays the membrane potential distribution and equilibrium potentials. - **Conductance Profiles** (`MakeCRGraph`): Illustrates conductance densities of different channel types as a function of dendritic length. - **Current Densities** (`MakeJRGraph` and `MakeIRGraph`): Compute current densities (`CalcJm` for membrane current density in microamperes/cm² and `CalcI` for current in pA/μm), providing insights into the local electrical activity along the dendrites. ### Summary The model aims to explore how persistent conductances and different ion channels influence the electrical properties of dendritic trees. This is done by providing spatially distributed data on membrane potential, conductance, and current, highlighting the role of dendrites in neuronal computation and integration. The computational approach provides insights into how tonically active conductances modulate dendritic processing and, ultimately, neuronal function.