Bioelectricity

Bioelectricity refers to the electric potentials and currents generated by or occurring within living organisms, forming a critical intersection of biophysics and biochemistry. It arises from the controlled movement of ions like sodium, potassium, and calcium across cell membranes via specialized proteins known as ion channels and pumps. This process creates an electrochemical gradient and establishes a membrane potential, a voltage difference that is fundamental to cellular function. In excitable cells, such as neurons and muscle cells, rapid, transient changes in this potential, known as action potentials, serve as the primary mechanism for nerve impulse transmission, muscle contraction, and intercellular communication.

1. Fundamentals of Bioelectricity
   1. The Cellular Environment
      1. The Plasma Membrane
         1. Phospholipid Bilayer Structure
            1. Amphipathic Nature of Phospholipids
            2. Membrane Fluidity
            3. Membrane Asymmetry
            4. Cholesterol Effects on Membrane Properties
         2. Electrical Properties of the Membrane
            1. Role as an Insulator
            2. Capacitive Properties
            3. Membrane Thickness and Capacitance Relationship
            4. Dielectric Constant of Biological Membranes
         3. Membrane Proteins
            1. Integral Proteins
            2. Peripheral Proteins
            3. Transmembrane Proteins
            4. Protein-Lipid Interactions
            5. Functions of Membrane Proteins
      2. Intracellular and Extracellular Fluids
         1. Composition of Intracellular Fluid
         2. Composition of Extracellular Fluid
         3. Differences in Ion Concentrations
         4. Osmotic Balance
         5. Water Movement Across Membranes
         6. Volume Regulation
      3. Major Physiological Ions
         1. Sodium (Na+)
            1. Distribution Across Membrane
            2. Role in Membrane Potential
            3. Physiological Functions
         2. Potassium (K+)
            1. Distribution Across Membrane
            2. Role in Membrane Potential
            3. Physiological Functions
         3. Calcium (Ca2+)
            1. Distribution and Storage
            2. Role in Signaling
            3. Intracellular Calcium Regulation
         4. Chloride (Cl-)
            1. Distribution Across Membrane
            2. Role in Membrane Potential
            3. Physiological Functions
         5. Other Important Ions
            1. Magnesium (Mg2+)
            2. Bicarbonate (HCO3-)
            3. Phosphate (PO4³-)
   2. Principles of Electrical Circuits in Biology
      1. Voltage (Potential Difference)
         1. Definition and Units
         2. Biological Sources of Voltage
         3. Measurement of Voltage
      2. Current (Ion Flow)
         1. Definition and Units
         2. Direction of Current Flow
         3. Relationship to Ion Movement
         4. Conventional vs. Electron Flow
      3. Resistance and Conductance
         1. Definition of Resistance
         2. Definition of Conductance
         3. Factors Affecting Membrane Resistance
         4. Relationship to Ion Channel Activity
         5. Temperature Effects on Resistance
      4. Capacitance
         1. Definition and Units
         2. Biological Capacitance
         3. Role in Membrane Time Constant
         4. Charging and Discharging of Membrane Capacitor
      5. Ohm's Law in Biological Systems
         1. Application to Membrane Currents
         2. Limitations in Biological Systems
      6. Equivalent Circuit Models
         1. Simple RC Circuit Model
         2. Hodgkin-Huxley Circuit Model
   3. Ion Transport Mechanisms
      1. Diffusion and Gradients
         1. Chemical Gradient
            1. Concentration Differences
            2. Driving Force for Diffusion
            3. Fick's Laws of Diffusion
         2. Electrical Gradient
            1. Membrane Potential Influence
            2. Electrostatic Forces
            3. Electric Field Effects
         3. Electrochemical Gradient
            1. Combined Chemical and Electrical Forces
            2. Nernst Potential
            3. Driving Force Calculation
      2. Passive Transport
         1. Simple Diffusion
            1. Lipid Solubility Requirements
            2. Permeability Coefficients
         2. Ion Channels
            1. Structure of Ion Channels
            2. Selectivity Filter
               1. Ion Selectivity Mechanisms
               2. Size Selectivity
               3. Charge Selectivity
            3. Gating Mechanisms
               1. Voltage Gating
               2. Ligand Gating
               3. Mechanical Gating
               4. Temperature Gating
            4. Channel Kinetics
               1. Opening and Closing Rates
               2. Single Channel Conductance
            5. Channelopathies
         3. Facilitated Diffusion
            1. Carrier Proteins
            2. Transport Kinetics
            3. Saturation Kinetics
      3. Active Transport
         1. Primary Active Transport
            1. Ion Pumps
               1. Structure and Function
               2. Energy Requirements
            2. ATPases
               1. Sodium-Potassium ATPase
               2. Calcium ATPase
               3. Proton Pumps
               4. ATP Hydrolysis Mechanism
         2. Secondary Active Transport
            1. Cotransporters (Symporters)
            2. Exchangers (Antiporters)
            3. Examples in Physiology
            4. Energy Coupling Mechanisms