4. Hard Cards

• Xo is the molar concentration outside of the cell, Xi is the molar concentration inside of the cell
• Nernst equation


  Equation for calculating the equilibrium potential (Ex) of an ion, as well as predicting in which direction ions will move when under certain conditions
• Ex = RT/zF ln(Xo/Xi)


  Nernst equation
• 8.314 j/k*mol


  R in the Nernst equation, ideal gas constant
• Temperature in Kelvin


  T in the Nernst Equation
• Charge of the ion


  z in the Nernst equation
• Ex ~= 61/z log(Xo/Xi)


  Back of the envelope equation for calculating the equilibrium potential
• Vm = RT/F ln( (pk[K+]o + pna[Na+]o + pcl[Cl-]i) / (pk[K+]i + pna[Na+]i + pcl[Cl-]o) )

  GHK equation
• Goldman-Hodgkin-Katz equation


  GHK equation
• Px


  Permeability (ability of an ion to cross a membrane through ion channels under at any given point)
• Graded potentials


  Change in membrane potential that is not enough to pass the signal forward
• Depolarization


  When the Vm goes from a negative to a more positive potential
• Hyperpolarization


  When the Vm of a cell membrane gets more negative
• Postsynaptic potentials (PSPs)


  Presynaptic neurons that release small amounts of naurotransmitters along dendrites causes small amounts of ion movement through postsynaptic ligand-gated ion channels, causing small Mv deviations
• Excitatory postsynaptic potentials (EPSPs)


  PSP caused by the release of excitatory neurotransmitters that causes slight depolarization
• Inhibitory postsynaptic potentials (IPSPs)


  PSP caused by the release of inhibitory neurotransmitters that caust slight hyperpolarization
• EPSPs = depolarization, IPSPs = hyperpolarization
• Spatial summation


  When two small EPSPs from adjacent inputs are triggered which might get you over the AP threshold
• Temporal summation


  When multiple EPSPs from the same input occur close enough together that their decay periods overlap so the depolarization compounds into a big enough charge that the AP threshold is reached
• Depolarization from incoming neurons (AP step 1 )


  When EPSPs cause enough depolarization to reach the AP threshold
• Opening of voltage-gated Na+ channels (AP step 2 )


  Na+ channels open with depolarization, and because the cell is still negative and the Na+ is lower concentration inside of the cell, they flood in, giving the cell even more positive charge
• Opening of voltage-gated K+ channels (AP step 3 )


  Once the Vm of the cell has depolarized enough to be positive, K+ floods out of the cell with its electrochemical gradient, assisted by the opening of more K+ channels, which makes it more negative than its resting potential
• Inactivation of voltage-gated Na+ channels (AP step 4 )


  When the membrane reaches a positive potential the Na+ gates close, stopping any further entrance of the excitatory ions
• Deactivation of voltage-gated K+ channels (Ap step 5 )


  Once the Vm becomes negative again, the K+ ions are stopped from leaving the cell as quickly, so the hyperpolarizing current stops and the Vm will slowly return to the equilibrium of resting potential
• Chronic pain Na+


  When a change in voltage-gated Na+ channels causes too much excitability in pain-sensing neurons
• Allodynia


  Experiencing pain despite not experiencing injurious stimuli due to disregulation in the somatosensory system
• Afterhyperpolarization


  -70 mv to -80 mv and back to -70 mv lasting for a few milliseconds to return back to equilibrium is caused by the gradual closing of K+ gates
• Absolute refractory period


  1/2 - 1 millisecond where there cannot be another action potential because the Na+ gates are inactivated, preventing them from getting any inward excitatory current
• Relative refractory period


  When it is more difficult for an AP to happen because only some of the NA+ gates have reopened and many of the K+ gates are still open, leaving a cell at slightly lower Vm
• Myelin increases conduction velocity by physically blocking K+ leak channels, trapping the positive charges within the axon and causing the charges to move faster
• Saltatory conduction


  Signal changes detected at intervals (ranvier nodes)
• Anaglesia


  Inhibitor of voltage-gated Na+ channels, stopping neurons from reaching action potential and stopping sensory inputs from being sensed
• Lidocaine


  Common type of anaglelsia
• Tetrodotoxin (TTX)


  Toxin sodium channel inhibitor present in pufferfish that spreads throughout the body and stops neurons from communicating. If left for too long, the diaphragm stops getting signals and you asphyxiate. 1 milligram can kill a person from respiratory failure within hours
• Phrenic nerve


  Efferent signalling pathway that tells the diaphragm to move up and down