BME 603 - Ch. 3

medicineman's version from 2016-02-01 01:31


Question Answer
Action potentialThe signal conducted by axons. Has a fixed size and duration and occurs at the cell membrane. Cells that are capable of generating and conducting action potentials have an excitable membrane
Resting membrane potentialThe difference in electrical charge across the cell membrane when it is not generating impulses
WaterHydrogen and oxygen molecules are held together by polar covalent bonds. This polarity makes water an effective solvent of other polar molecules
Ions Atoms or molecules that have a net electrical charge. Monovalent ion - difference between protons and electrons is one. Divalent - difference between protons and electrons is two
CationIon with a net positive charge (sodium, potassium, calcium)
AnionIon with a net negative charge (chloride)
Hydrophilic A substance that is water soluble (polar)
HydrophobicA substance that is not water soluble (nonpolar)
Phospholipid bilayer The neuronal membrane consists of a sheet of phospholipds two molecules thick. The hydrophilic heads face out and the hydrophobic tails face each other
EnzymeCatalyzes chemical reactions in cells
Peptide bondsJoin the amino group of one amino acid to the carboxyl group of the next
PolypeptidesMade of a single chain of amino acids
Primary structure of a proteinChain of amino acids linked by peptide bonds
Secondary structure of a proteinThe polypeptide chain coils into an alpha helix
Tertiary structure of a proteinInteractions among the R groups cause the molecule to change its three-dimensional shape further
Quaternary structure of a proteinDifferent polypeptide chains bond together to form a larger molecule. Each polypeptide contributing to a protein with a quaternary structure is called a subunit
Channel proteinsSuspended in phospholipid bilayers with the hydrophobic portion inside the membrane and the hydrophilic ends exposed to the watery environments on either side
Ion channelsTypically made of four to six subunits. The subunit composition determines the properties of the channel
Ion selectivitySpecified by the diameter of the channel and the nature of the R groups lining it
GatingChannels with this property can be opened and closed by changes in the local microenvironment of the membrane
Ion pumpsUse the energy released in the breakdown of ATP to transport certain ions across the membrane
DiffusionNet movement of ions from regions of high concentration to regions of low concentration
Concentration gradientDifference in concentration across a permeable membrane
Electrical current The movement of electrical charge. Represented by the symbol I and measured in amperes
Electrical potential (voltage)The force exerted on a charged particle. Reflects the difference in charge between the anode and the cathode. Represented by the symbol V and measured in volts
Electrical conductance The relative ability of an electrical charge to migrate from one point to another. Represented the by the symbol g and is measured in siemens (S). Depends on the number of ions or electrons available to carry electrical charge and the ease with which these charged particles can travel
Electrical resistanceThe relative inability of an electrical charge to migrate. Represented by the symbol R and measured in ohms. Resistance in the inverse of conductance (R=1/g)
Ohm's lawI=gV
Membrane potentialThe voltage across the neuronal membrane represented by Vm
MicroelectrodeFilled with an electrically conductive salt solution and connected to a volt meter. Tip fine enough that it can penetrate the neuronal membrane
Ionic equilibrium potential (equilibrium potential)The electrical potential difference that exactly balances an ionic concentration gradient
Large changes in membrane potential are caused by minuscule changes in ionic concentrations
The net difference in electrical charge occurs at the inside and outside surfaces of the membraneThis occurs because the phospholipid bilayer is so thin
Ions are driven across the membrane at a rate proportional to the difference between the membrane potential and the equilibrium potentialThe difference between the real membrane potential and the equilibrium potential for a particular ion is called the ionic driving force
If the concentration difference across the membrane is known for an ion, the equilibrium potential can be calculated for that ion
Nernst equationCan be used to calculate the value of the equilibrium potential for a specific ion
Distribution of ions across the membranePotassium more concentrated on the inside, and sodium and calcium are more concentrated on the outside
Sodium-potassium pumpBreaks down ATP in the presence of internal sodium ions. Exchanges internal sodium ions for external potassium ions. Estimated to expend as much as 70% of the total amount of ATP utilized by the brain
Calcium pumpActively transports calcium ions out of the cell
Goldman equationUsed to calculate the resting membrane potential. Takes into consideration the relative permeability of the membrane to different ions
DepolarizationA change in membrane potential to a less negative value
Blood-brain barrierSpecialization of the walls of brain capillaries that limits the movement of potassium and other bloodborne substances into the extracellular fluid of the brain
Potassium spatial bufferingWhen the external concentration of potassium increases in the brain, potassium enters astrocytes via membrane channels thereby dissipating the potassium over a large area