Chapter 5 - Guyton Flashcards
Membrane potentials are caused by what?
diffusion
Define diffusion potential.
ion concentration difference on the two sides of the membrane, ex. potassium concentration greater within a nerve fiber membrane than on the outside on the membrane, strong tendency for potassium to diffuse out, eventually the diffusion potential is great enough to block further net potassium diffusion)
Normal potential difference required in mammalian nerve fiber for potassium is:
94mV (negative inside the fiber)
Normal potential difference required in mammalian nerve fiber for sodium is:
61 mV (positive inside the fiber)
Nernst Potential
diffusion potential across a membrane that exactly opposes the net diffusion of a particular ion through the membrane, determined by ratio of concentrations of specific ion on two sides of the membrane
When membrane is permeable to different ions, the diffusion potential depends on these factors:
1) polarity of the electrical charge of each ion; 2) permeability of the membrane to each ion; 3) concentrations of the respective ions on the inside and outside membrane
Goldman Equation
gives the calculated membrane potential on the inside of the membrane when two univalent positive ions (sodium and potassium) and one univalent negative ion (chloride) are involved
Sodium, potassium, and chloride are the most important ions in membrane potential development. The degree of importance is determined by:
it is proportional to the membrane permeability of each ion, the resting potential is closest to the equilibrium potential for the ion with the highest permeability (ex. if potassium and chloride can’t get through then Nernst equation of sodium will determine entire membrane potential)
What is primarily responsible for signal transmission in neurons?
rapid changes in sodium and potassium permeability
What instrument is used to measure the membrane potential?
voltmeter
Resting membrane potential
-90mV (inside is 90mV more negative than outside)
Leakage of potassium through nerve membrane
far more permeable to potassium than sodium (100 times more) but can leak through, key factor in determining the level of normal resting membrane potential
Which contributes more to the resting membrane potential, sodium or potassium?
potassium (K+ Nernst potential = -94mV)
Using Goldman equation because sodium and potassium interact, potential inside the membrane would be -86mV. Why is it -90mV?
contribution of the sodium-potassium pump, more sodium pumped out than potassium in, causing continual loss of positive charge in the cell
Resting stage of action potential
before the action potential begins, membrane is polarized at -90mV