Nernst Equation Lab Report

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The purpose of this experiment is to investigate the ionic basis of the neuron’s resting membrane potential (Vm). We examine how this potential is affected by potassium ion [K+] concentration and permeability using Orconectes rusticus crayfish abdominal muscles, and we ask whether or not the Nernst Equation solely based on [K+] can also predict the cell’s resting membrane potential. We predicted that [K+] concentration had a significant influence on the membrane potential and thus the Nernst Equation was an accurate predictor of the observed Vm changes. Our results indicate that our hypothesis was incorrect- the results indicate that the Nernst equation calculations did not correspond with the observed resting membrane potentials. This outcome …show more content…
They do this essential work by generating a constant exchange of ions across the cell membrane. The more we understand this process, the better we can investigate issues like brain-based disease and treatment. In order to understand exactly how this communication is performed, we must decipher the ionic basis of the neuronal membrane. There are two main factors that dictate this movement: the chemical and electrical gradients. Chemical gradient refers to the concentration differences of ions across the membrane while electrical gradient describes the membrane’s selective permeability to specific ions. Together, they combine to create the electrochemical gradient. The difference between the two is known as the cell’s resting membrane potential (Vm) and represents the cell’s potential for doing work. The resting membrane potential includes how the concentration and permeability of all present ions affect the electrochemical gradient of the membrane. These ions include sodium [Na+], chloride [Cl-], and potassium [K+] (Strickholm and Wallen …show more content…
Crayfish are an excellent model organism for a muscle neuron because they are easily dissected, they have an abdomen small enough to handle but large enough to fairly easily perform selective penetrations through the membrane, and this muscle remains stable in a standard saline solution for several hours. They are also a sensible economic choice considering their low cost and maintenance prices (Baierlein et. al 2011). Changes to the extracellular environment were performed by bathing the muscle in solutions with different concentrations of potassium [K+]. A typical neuron membrane at rest is more negatively charged, intracellular relative to extracellular environment at 140 mV (Baierlein et. al 2011). Previous knowledge of normal equilibrium potentials for various ions proved to be imperative information for deciphering our results. We referenced extracellular (Eqout) and intracellular (Eqin) concentrations (MM) of giant squid neurons to predict crustacean cells at rest, Eqout[K+]=20, Eqin[K+]=400, Eqout[Na+]=440, [Na+]in=50, Eqout[Cl-]=560, Eqin[Cl-]=40-150 (Purves et. al

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