NEUR 0010 - Chapter3 Flashcards
How do action potentials contrast with passive electrical signals?
Don’t diminish over distance, fixed size and duration; similar to Morse code
What is resting membrane potential?
The difference in electrical charge across a membrane; negative inside compared to outside
What is the action potential?
A reversal of the resting membrane potential: depolarizes, makes it positive inside compared to outside
What are the three main components that determine resting membrane potential?
Salty fluid bathing the membrane, the membrane, and the proteins in the membrane
Why is it significant that the cytosol surrounding the neuronal membrane is composed mostly of water?
Because water is polar covalent: makes water an effective solvent of charged/polar molecules, which allows for ions
What are three examples of protein use in the neuronal membrane?
Enzymes, cytoskeleton, and receptors
What are the two most important functions/characteristics of ion channels in the neuronal membrane?
Ion selectivity and gating abilities
What two conditions are required to allow ions to diffuse across a membrane?
The appropriate channels are present, and the appropriate concentration/electrical gradient is available to drive the ions over to whatever side
What are the two main ways to move ions across a membrane?
Diffusion by concentration gradient, or by electrical field
What is positive electrical current?
Current in the direction that positive charges move: from anode (+) to cathode (-)
What are two important factors in determining ion movement through electric field?
Voltage (electric potential) = force exerted on a charge particle, determined by the different in charge between anode and cathode; and Conductance: ability of electrical charge to migrate from one point to another, depends on the electrical properties of the conducting substance, inverse of resistance
What is the typical resting membrane potential for a neuron?
-65 mV
What is equilibrium potential?
The potential establish when diffusion and electrical potential balance each other out: K+ ions move outside because of concentration gradient, but then are pulled back in by the large negative voltage inside the cell
What is the typical equilibrium potential for a neuron?
-80 mV
What size concentration gradient change is required to make a significant membrane potential change?
Tiny: miniscule ion concentration changes can cause huge shifts in membrane potential
Why can a membrane store electrical charge and have capacitance?
Because it’s so thin: negative and positive ions are attracted to each other through the membrane, so cluster close to it, allowing charge to be localized near the membrane inner and outer surfaces
What is the ionic driving force?
The difference between real membrane potential and the equilibrium potential )or Vm - Eion) for a particular ion
What can be calculated from knowing the concentration difference across the membrane for a specific ion?
The equilibrium potential: whether it’s positive or negative, or exact value by Nernst equation
What is the Nernst equation used for?
Calculating the value of the equilibrium potential for an ion using charge, temperature, and ratio of external and internal ion concentrations
What is the Nernst equation?
Eion = (2.303)(RT/zF)log(ionO/ionI)
What are the concentration distributions of K+, Na+, and Ca2+?
K+ concentrated on inside; Na+ and Ca2+ concentrated on outside
How does the sodium potassium pump work?
Exchanges internal Na+ for external K+: 3 Na+ moves out, 2 K+ moves in
How does the calcium pump work?
Drives Ca2+ out of the cytosol
Why is the resting membrane potential closer to K+’s eq. pot. instead of Na+’s eq. pot, if the membrane is permeable to both ions?
Because it’s more permeable to K+ than Na+, so more K+ driven out than Na+ can leak in
What is a pore loop?
The region in an ion channel subunit (here, K+ channels) that contributes to the selectivity filter to only allow K+ through
How are neurons depolarized by K+?
Increasing outside concentration of K+ depolarizes neurons: makes it less negative
How do astrocytes affect extracellular K+ concentration?
Pump K+ into their own cytosol to remove it from ECF: this increased internal K+ concentration in astrocytes is dissipated by the astrocytic processes network: potassium spatial buffering!
