The Neuronal Membrane at Rest Flashcards
action potential
— spike, discharge, nerve impulse
— a brief fluctuation in membrane potential caused by the rapid opening and closing of voltage-gated ion channels
— “information is encoded in the pattern of electrical impulses”
excitable membrane
— any membrane with the capability of generating axon potentials
resting membrane potential
— the membrane potential (membrane voltage) maintained while a cell is not generating action potentials
— ≈ -65 mV
polar covalent bond
— a covalent bond where electrons are unequally shared
— example: H20 provides more electrons to oxygen’s outermost shell, making it polar, and thus making it a solvent of ionic substances
ion
— an atom or molecule with a net electrical charge due to difference in number of protons (atomic number) and electrons
ionic bond
— complete transfer of valence electrons between atoms, resulting in two oppositely charged ions
sphere of hydration
— “cloud” of water molecules surrounding ions in a solution, effectively insulating ions from one another
cation v. anion
— cations have net positive charges: Na+ and K+ (monovalent cations), and Ca2+ (divalent cation)
— anions have net positiv charges: Cl- (monovalent anion)
nonpolar covalent bond
— occurs when shared electrons are distributed evenly, giving a substance no net electrical charge
lipids
— class of water-insoluble biological molecules important to the structure of cell membranes
phospholipids
— lipids containing long nonpolar chains of carbon atoms bonded to hydrogen atoms, with a polar phosphate group
phospholipid bilayer
— arrangement of phospholipid molecules forming the basic structure of the cell membrane
R group
— substituent of amino acids determining the chemical relationships in which the amino acid can participate
peptide bond
— covalent bond between the amino group (NH3+) of one amino acid to the carboxyl group (COO-) of another
— synthesizes one water molecule
polypeptide
— a string of amino acids held together by peptide bonds
protein structure I
— “primary”
— the sequence of amino acids in the polypeptide
protein structure II
— “secondary”
— coiling of a polypeptide into an alpha helix (α-helix)
protein structure III
— “tertiary”
— three-dimensional folding of a polypeptide
protein structure IV
— “quaternary”
— different polypeptides bonded together to form a larger protein
subunit
— each polypeptide contributing to the quaternary structure of a large protein
— subunit composition variations determine channel properties
ion channels
— a membrane-spanning protein forming a pore and allowing the passage of ions from one side of the cellular membrane to the other
— typically requires 4-6 protein molecule subunits
ion selectivity
— a property of most ion channels , specified by pore diameter and R group nature
— creates selective permeability towards specific ions
gating
— property of ion channels where opening or closing occurs in response to specific signals, such as membrane voltage or neurotransmitter presence
ion pumps
— enzymes using energy released from ATP breakdown to transport certain ions across the membrane
diffusion
— temperature-dependent movement of molecules from high concentration to low concentration
— happens when membrane has channels permeable to the ion and if there is a concentration gradient across the membrane
concentration gradient
— difference in concentration from one region to another
— ionic concentration gradients help determine membrane potential
concentration
— expressed as molars (M), the number of molecules per liter of solution
— M = mol/L
— mM = 0.001 mol/L
— for example: [NaCl] = 1mM means “The concentration of the sodium chloride solution is 1 millimolar.”
electrical current
— represented by the symbol I (from french: intensité de courant, meaning “current intensity”)
— the rate of movement of electrical charge
— measured in amperes (amp)
— quantity of current determined by electrical potential and electrical conductance
electrical potential
— voltage (V) aka potential difference
— the force exerted on an electrically charged particle (ion)
— reflects difference in charge between anode (+) and cathode (-)
— higher voltage = larger electrical current
electrical conductance
— symbol: g
— relative ability of an electrical charge to migrate from one point to another
— inverse of resistance (R)
— SI unit: siemens (S)
electrical resistance
— symbol: R
— relative inability of an electrical charge to migrate from one point to another
— inverse of conductance (g)
— SI unit: ohms (Ω)
Ohm’s law
— the relationship between electrical current (I), voltage (V), and conductance (g)
— I = gV
— since g = 1/R , Ohm’s law can be expressed another way:
— I = V/R or V = IR
— Ohm’s law shows that if either conductance or potential difference is zero, no electrical current will flow
membrane potential
— Vm (subscripted m)
— the voltage across a cell membrane at any given moment, measured in mV
microelectrode
— probe measuring electrical activity of cells
— filled with conductive salt solution and connected to voltmeter
voltmeter
— measures potential difference/electrical potential/voltage between microelectrode tip (inside cell) and wire (outside cell)
ionic equilibrium potential
— the electrical potential difference (voltage) exactly balancing an ionic concentration gradient
capacitance
— the ability of the membrane to store electrical charge
ionic driving force
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