about Ci= 10-3 uscle cells. Detemine 2. The restine iular space but is very low (Cout =10 ual AV for calcium. Suppose diffusion temperature T moie/ii . uiu iembrane 3. Equilibrium membrane potential for potassium ions is AV = 89 mV. Find concentration of potassium ions inside the neuron cell Cin if its concentration in the extracellular space is Cout = 12 mmole/liter. Suppose diffusion temperature T = 20°C. 0a ".l 6217:54 PM 3G Vodafone UA Electricity.pdf BIOELECTRICITY. MEMBRANE POTENTIALS 1. Electrical charge. There are only two types of charge, which we call positive (proton) and negative (electron). Charge of electron and proton is e =1.6×10-1º C. Mass of electron 9.1×10-3' kg and mass of proton 1.67x10" kg. Then, electrical charge is q = Ne, here N amount of charged particles. 2. The electric field E is defined to be E = =, where F is the Coulomb or electrostatic force exerted on a small positive test charge q . E has units of N/C. The magnitude of the electric field E created by a point charge q is F = k, where r is the distance from q . The electric field E is a vector and fields due to multiple charges add like vectors. 3. The potential difference between points A and B, VB – VA , defined to be the change in potential energy of a charge q moved from A to B, is equal to the change in potential energy divided by the charge, ДРЕ Potential difference is commonly called voltage, represented by the symbol AV: AV = 4. In uniform electric field the potential difference is AV = Ed, where E is electric field and d is the distance from A to B, or the distance between the plates. 5. A capacitor is a device used to store charge. The amount of charge q a capacitor can store depends on two major factors - the voltage applied and the capacitor's physical characteristics, such as its size. The capacitance C is the amount of charge stored per volt, or C = units Farad (F). EE9A 6. Capacitance of a parallel plate capacitor C = 4, where ɛ, = 8.85 · 10-12 F/m is called the permittivity of free space, & is the dielectric constant of the material, A is area of plates and d is distance between plates. 7. Capacitors are used in a variety of devices, including defibrillators, microelectronics such as calculators, and flash lamps, to supply energy. The energy stored in a capacitor can be expressed in three CΔν2 qΔν ways: Energy = of the capacitor(F). 8. Electric current I is the rate at which charge flows, given by I = , units Amperes (A). Here q is , where q is the charge (C), AV is the voltage (V), and C is the capacitance the amount of charge passing through an area in time t . Membrane 9. Membrane potential is potential difference between inner and outer surface of biological membrane. The semipermeable membrane of a cell has different Na* Inside Coulomb force Diffusion concentrations of ions inside and out. Diffusion moves the Outside K* and Cl- ions in the direction shown, until the Coulomb force halts further transfer. This results in a layer of positive charge on the outside, a layer of negative charge on the inside, and thus a voltage across the cell membrane. At rest state, the membrane is normally impermeable to Na*. If Coulomb force Diffusion Coulomb force Diffusion membrane is permeable only to one ion type, the membrane potential is determined by equation: RT In- Cin AV = here R = 8,31J/(mole·K) is gas constant; T is the temperature of diffusion (K); Cout F = 96500 C/mole is Faraday's constant, Z is valence of ion (Z = 1 for K+, Na*, Cl¯), Cin is the ions concentration inside the cell (mole/m³) and Cout is the ions concentration outside the cell (mole/m³). If membrane is permeable_ simultaneously to three ion types, then the membrane potential is found by equation: RT, P«C% + PNaCa + PciC6ut -In- AV = - ZF"PxCK + PNaCout + PciCin here Px, PNa, Pcı are permeability of the membrane to corresponding ion type C , Cia, c concentrations inside the cell (mole/m³) and Cout, Cout, Cout are corresponding concentrations outside the cell (mole/m³). , Cin are ions Relationship between membrane permeability at equilibrium Px:PNa:Pci = 1: 0.04: 0.45. Relationship between membrane permeability during action potential Pg:PNa:Pci = 1:20: 0.45. 10. Resistance and Resistivity The resistance R of a cylinder of length L and cross-sectional area A is PL where o is the resistivity of the material.