lab 2 - Crayfish Muscle Resting Membrane Potential...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Crayfish Muscle Resting Membrane Potential The risks associated with this laboratory exercise are minimal, but sharp instruments can always cut, glass can break and plastic syringes can come apart during use. A little care and attention can prevent accidents. Like any other animal, crayfish may carry diseases, although these are only rarely transmitted to people. Nevertheless, please wear the disposable gloves that have been provided, keep your hands away from your nose and mouth while performing the dissection and wash your hands when you are finished. Finally, the instrumentation you will be using has been carefully designed to protect you against electrical shocks. Please do not compromise this protection by changing the set-up except as indicated in the manual. OBJECTIVES •To measure the resting membrane potential (Em) of crayfish muscle cells using glass micropipettes. •To study the effect of varying the extracellular potassium ion concentration on the membrane potential. •To study the effect of solutions containing tetraethyl ammonium chloride (TEA) on the membrane potential. BACKGROUND All cells under resting conditions have an electrical potential difference across the plasma membrane such that the inside of the cell is negatively charged with respect to the outside. This potential is the resting membrane potential ; its magnitude depends on the type of cell, but usually ranges between -60 and -90 mV. By convention, the polarity (positive or negative) of the membrane potential is stated in terms of the sign of the excess charge on the inside of the cell. The membrane potential can be accounted for by the fact that there is a slightly greater number of negative charges than positive charges inside the cell and a slightly greater number of positive charges than negative charges outside. The excess negative charges inside the cell are electrically attracted to the excess positive charges outside the cell, and vice versa. Thus, these excess ions collect along a thin shell on the inner and outer surfaces of the plasma membrane, whereas the bulk of the intracellular and extracellular fluid is electrically neutral. The total number of positive and negative charges that have to be separated across the membrane to account for the potential is an insignificant fraction of the total number of charges actually in the cell. The resting membrane potential is determined mainly by two factors: • the differences in ion concentration of the intracellular and extracellular fluids and • the relative permeabilities of the plasma membrane to different ion species. Sodium, potassium, and chloride ions are present in the highest concentrations and therefore generally play the most important roles in the generation of the resting membrane potential. Physiology Department – McGill University 2010-2011
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/16/2011 for the course PHGY 212 taught by Professor Juliomartineztrujillo during the Fall '10 term at McGill.

Page1 / 14

lab 2 - Crayfish Muscle Resting Membrane Potential...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online