The code provided is a computational model designed to simulate the dynamics of neuronal volume and the associated membrane potential changes when a stimulation current is applied. It is based on the biological processes involved in neuronal excitability and ion exchange across the cell membrane. Here are the key biological aspects of the model: ### 1. **Neuronal Volume Dynamics** - **Cellular Structure:** The neuron is modeled as a spherical cell, defined by its diameter. Changes in cell volume can be simulated and observed in response to electrical stimuli. - **Volume Changes:** The model considers the relative changes in cell volume (`DV`) due to ionic fluxes and water movement, which are critical during neuronal activity where cell swelling or shrinking might occur. ### 2. **Membrane Potential (Vm)** - **Resting Membrane Potential:** The initial state of the membrane potential is set to a typical resting value of -67 mV, reflecting the polarized state of the neuron at rest. - **Ionic Currents:** The model includes ionic currents of potassium (K) and sodium (Na) ions, which are pivotal to generating action potentials. These currents are determined by the conductivities of their respective ion channels (`gK0`, `gN0`) and their equilibrium potentials. ### 3. **Ion Concentrations** - **Intracellular and Extracellular Concentrations:** The starting concentrations for K and Na ions inside and outside the cell are specified, which are essential for establishing and maintaining the membrane potential. - **Active Pumps:** The Na-K pump activity is included (`jpK0`, `jpN0`), which is crucial for maintaining ionic gradients over time. ### 4. **Gating Variables and Ion Channels** - **Voltage-Gated Ion Channels:** The model includes gating variables (`n`, `m`, `h`) for the neuron, representing the probability of ion channels being open or closed. These are based on Hodgkin-Huxley formalism: - `n`: Relates to potassium channel activation - `m` and `h`: Relate to sodium channel activation and inactivation, respectively ### 5. **Stimulus Application** - **Stimulation Current (`Ie`):** A stimulation current is applied at a specified time, mimicking experimental conditions in which external currents are used to depolarize the neuron and evoke action potentials. ### 6. **Biophysical Constants and Parameters** - **Water Diffusion:** The movement of water across the membrane is considered in relation to osmotic balance and is influenced by the water diffusion coefficient (`dw`). - **Capacitance and Conductance:** The model considers membrane capacitance (`cm`) and other parameters to simulate electrical characteristics accurately. Overall, the model captures the intricate balance and interaction of electrical stimuli, ionic currents, and volume changes in neurons, providing insights into how neurons respond dynamically at the cellular level during stimulation. This contributes to our understanding of neuronal excitability and the underlying biophysical processes during neural activity.