Helena Parkington; Week 8 MED1011; Physiology
Electricity senses the environment through light, pressure, temperature and chemical reactions, and converts it into electricity (fast and discrete). Brownian motion is movement of particles in solution, which are in constant motion and in equilibrium. Charged particles are attracted to opposite charges. Concentration gradient drives
movement, potential difference is diffusion potential. If some particles can move through but others can't eg due to charge, not all will move through (non equilibrium diffusion potential). Cells develop and maintain electrical potential with Na, plasma membrane is not permeable to all ions. Cell membrane is hydrophobic, non-polar, ions cannot pass through. ICF is 12mM Na, 140mM K, 10mM Cl, protein. ECF is 140mM Na, 4mM K, 100mM Cl and 20mM HCO3. Ion concentrations contribute to membrane potential, there is the same osmolarity of total ions inside and out.
Nernst equation is Ex = (RT/zF) ln (Xo/Xi) app = 60log(Xo/Xi) where E is potential, R gas constant, T absolute temperature, F Faraday, z is charge on X, X is ion potential outside and that inside. It relates the concentration gradient of a cell to the electrical gradient that balances it. It calculates the potential of an ion of charge z across a membrane. It is also known as the equilibrium potential.
Goldman-Hodgkin-Katz equation calculates resting membrane potentials, by looking at the potentials of all ions together. p is permeability determined by number of ion channels open. Outside and inside differences of ions are maintained by transporters.
Potassium is -89mV, Na is 64mV, Cl is -74mV. Uneven distribution is due to semipermeable membrane, transmembrane movement of ions. Potassium channels are mostly open at rest, Na channels are mostly closed at rest. Inside of the cell is negative, -30 to -90mV. Ion channels are transmembrane proteins, ions pass through down electronegative gradient, selective for particular ions or range of ions. Inactivation gate may be present and ion channels permit fast transmembrane flux of ions.
There are ligand gated ion channels, voltage gated ion channels, mechanically gated ion channels (many in tough), leak channels are pretty much always open. Pumps/transporters are also transmembrane proteins, consume energy, establish ionic differences and resting membrane potential then maintain these. Ion channels open decreases resistance (R), moving across channel creates current (I), change in membrane potential = V. Ohm is V = IR.