4. Electrical Properties

• Protein channels that select for a type of ion will be lined with molecules of the opposing charge (e.g. a Na+ filtering channel will be lined with negative glutamate residue so negatively charged ions will be repelled and can't get through)
• Hydration shell


  Cell pores with amino acid residues that stabilize certain ions enough to let them pass through water more easily, which lets them pick specific ions regardless of size
• Leak channels


  Ion channels that never close and let in a steady flow of their targeted ion
• Voltage-gated ion channel


  Ion channels that open and close depending on the membrane potential (e.g. Na+ channels staying closed when it's negative (resting potential) and only opening when it's positive (action potential))
• Ligand-gated ion channels (ionotropic receptors)


  Ion channels that open in response to binding to certain molecules (ligands) such as neurotransmitters
• Sensory channels


  Catch-all category of ion channels that open and close based on sensory stimuli (i.e. being stretched, exposed to light, distortion
• Electrical gradient


  The overall change of the cell attracts or repels ions based on their individual charge
• Chemical gradient


  Diffusion but make it ions; they move from areas of high concentration to low concentration
• Dynamic equilibrium


  Where there is net equilibrium but the ions are still flowing in and out of a cell because the electrochemical gradient's forces are balancing each other out completely
• Equilibrium potential


  Place where the flow of ions into the cell is equal to the flow of ions out of the cell. Abbreviated Vm and Ex
• Reversal potential


  Another name for Ex based on the principle that once that threshold is crossed the net ion flow will be flipped
• Biological temperatures are usually close to 310 Kelvin
• 96845 Coulombs / mol


  Faraday's constant, F in the Nernst equation
• Action potential


  Short lasting change in membrane potential that travels down the axon that is the neurons primary way of communicating with each other, and trigger neurotransmitter release at the axon terminals at the end of a chemical synapse
• Action potentials are all or nothing, meaning that they either pass or not pass. If the charge isn't big enough, no signal is transmitted, and it is called a graded potential
• Action potentials typically last 1 to 2 milliseconds
• -70 mv


  Average resting potential
• Action potential has the characteristic shape of a very rapid depolarization (enough to cross the AP threshold) followed by prolonged hyperpolarization before repolarizing and returning to the resting membrane potential
• -55 mv


  Average action potential threshold
• Change in membrane potential during action potential is driven by the movement of ions, usually sodium and potassium
• Inactivation of the Na+ channels takes less than a millisecond, while deactivation of K+ channels takes a few milliseconds
• Depolarization


  -70 mv to +40 mv change in Vm that lasts for half a millisecond because of rapid Na+ ion uptake. At this stage the voltage-gated K+ channels also start to open
• Repolarization


  +40 mv to -70 mv after Na+ gates are closed and K+ gates are open. Lasts 1/2 millisecond
• Na+ travels down the axon because it's going down the gradient; it wants to be in areas of low concentration (axon) so it moves through channel gates, which are at each node of Ranvier. Once an area is depolarized, the gate closes behind it, so the only direction the ions can move is forward
• Conduction velocity


  The speed at which an AP travels down the length of an axon
• In order for a charge to reach AP there has to be some ion influx, which happens with Na+ ions at the nodes of Ranvier which are very dense with sodium gated channels