Human Physio Notes Week 2 - IA Adrian Bahn BIPN 100 Dr...

Info icon This preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
IA: Adrian Bahn BIPN 100 – Dr. Fortes 01/11/16 Ion Pumps Epithelial Transport Membrane Potentials Nernst Equation: Equilibrium Potentials Goldman-Hodgkin-Katz Equation (GHK) Graded Potentials Action Potentials – Generation Conduction As mentioned before, you can think of the ion disequilibrium as a battery. Since normally there is more positive charge concentrated outside the cell, there is an electrical gradient (a voltage) between the extracellular fluid (ECF) to the intracellular fluid (ICF) just like the positive and negative poles of an electrical battery. Think of a battery with a conducting wire connecting the two poles, except the wire is cut; no charge can flow from the negative to positive end and there is no current. This is exactly what happens with an impermeable cell membrane that separates the ions: there is nothing to conduct the current! However, the cell can fix the “cut wire” whenever it wants by making the membrane permeable to these charges (such as a sodium channel), letting the charges follow their electrochemical gradient. For some cells, the channels are closed until there is a signal, and for other cells the channels are always open; it all depends on the function of the cell and how they want to use this electrochemical potential energy. The Na+-K+ pump thus acts as a charger; it charges the electrochemical gradient (the battery) of the cell, and the ion channels are the wires that allow current to flow, letting the cell make use of this energy. Thus, the flow of ions entering the cell is an actual electrical current just like
Image of page 1

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

View Full Document Right Arrow Icon
IA: Adrian Bahn BIPN 100 – Dr. Fortes the electrical current that is probably charging or discharging your computer battery at this moment. Inside the cell, the potassium concentration is around 150 mM, whereas the extracellular potassium is 3.5-5 mM. The extracellular sodium is around 140 mM and the inside is 14 mM. Most cells have resting potassium leak channels that are open, allowing potassium to constantly leak out of the cell (contributing to the negative membrane potential of the cells). There are also Ca2+-ATPases located in the plasma membrane and the endoplasmic reticulum to remove Ca2+ in the cytoplasm, around 0.1 uM (100 nM), whereas Ca2+ in the ECF is around 1 mM. The contributions of anions are come in the form of impermeable proteins, nucleic acids, phosphates and phosphorylated compounds (such as glucose-6-phosphate), but the main permeable anion is chloride. Chloride anions are much higher in concentration outside the cell than inside. Keep in mind the direction of ion flow: generally, sodium wants to enter the cell and potassium wants to leave. Sodium entering gives the cell more positive charge, whereas potassium leaving gives the cell more negative charge. We’ll introduce the Nernst equation, its meaning, and explore it more next time. The Nernst equation is as follows: E ion E ion RT nF ln [ ion ] outside [ ion ] inside , where E is the potential, R is the universal gas constant, T is the absolute temperature in Kelvins, n
Image of page 2
IA: Adrian Bahn BIPN 100 – Dr. Fortes
Image of page 3

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

View Full Document Right Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern