The provided MATLAB code is designed to analyze extracellular action potentials (EAPs), focusing on their key features related to ion channel activities. The biological basis of this code is grounded in the electrophysiological properties of neuronal action potentials and the contributions of various ionic currents during these events. Here are the primary biological aspects the code is modeling: ### Key Biological Aspects 1. **Ionic Currents and Peaks:** - **Na+ Peak:** The rapid upstroke of the action potential is primarily due to the influx of sodium ions (Na+) through voltage-gated sodium channels. This phase is represented by the "na_peak" in the code, measuring the location and amplitude of the Na+ peak. - **K+ Peak:** Following the Na+ influx, potassium ions (K+) flow out of the neuron through voltage-gated potassium channels, which repolarizes and hyperpolarizes the cell membrane. This is reflected in the "k_peak" measurements in the code. - **Capacitive Peak:** The initial phase of the action potential often includes a capacitive component corresponding to the membrane charging, which is captured as the "cap_peak" in the code. 2. **Temporal Dynamics:** - The code measures the time between significant events in the action potential, specifically the time between the Na+ peak and the K+ peak (NA_K_TIME_COL). This is crucial for understanding the kinetics of ion channel activation and inactivation. 3. **Waveform Width:** - The measure of the waveform width at a specified percentage of its peak amplitude (25% in this case) helps provide insight into the duration and dynamics of action potential propagation. 4. **Derivatives and Decay Constants:** - **Rising Derivative to the Capacitive Peak:** This measures the rapidity of capacitance change as the neuron approaches the action potential threshold. - **K+ Phase Decay:** The exponential decay fitting after the K+ peak can reveal details about the deactivation of potassium channels and membrane repolarization processes. - **Repolarization Derivatives:** These metrics capture the maximum and minimum slopes of the EAP during repolarization, indicating how swiftly the membrane potential returns towards resting levels post-action potential. Collectively, this code provides a detailed analysis of the electrophysiological characteristics of neurons, focusing on components of the action potential as influenced by Na+ and K+ ion channel activities, and represents a foundational aspect of neuronal signaling and excitability analysis.