Mechanism of anoxic depolarization in the brain intracellular Na and Ca ions, and extracellular glutamate and aspartate. Glutamate and aspartate are normally present as the brain's primary excitatory neurotransmitters, but high concentrations activate a number of downstream apoptotic and necrotic pathways. This results in neuronal dysfunction and death. Neurons function in the central nervous system by generating signals from synapses, and this only works in the proper chemical environment. An electrical signal is mediated by the sodium channels and leaky potassium channels in which intracellular K ion concentration is higher than its corresponding extracellular concentration, whereas extracellular concentrations of Na, Ca, and Cl ions are higher than
Electrically powered spacecraft propulsion Electrically powered spacecraft propulsion An electrically-powered spacecraft propulsion system uses electrical energy to change the velocity of a spacecraft. Most of these kinds of spacecraft propulsion systems work by electrically expelling propellant (reaction mass) at high speed, but electrodynamic tethers work by interacting with a planet's magnetic field. Electric thrusters typically use much less propellant than chemical rockets because they have a higher exhaust speed (operate at a higher specific impulse) than chemical rockets. Due to limited electric power the thrust is much weaker compared to chemical rockets, but electric propulsion can provide a small thrust for a long time.