BIOD27H3 Chapter Notes -Extracellular Fluid, Reference Electrode

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17 Dec 2010

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Lecture 3 Mammilian physiology
Chapter 5 notes and chapter 8 notes.
K ions as well as negatively charged proteins are inside the cell (Higher K)
Na ions and Cl ions are outside of the cell. (Higher Na)
The inside of the cell is negatively charged compared to the extracellular (outside) which is positive. The reason for this is
because some of the proteins in the inside of the cell dont have matching cations (+) and some cations in the outside (which has a
net positive charge) dont have an anion to partner up with.
therefore, due to the differences in charge, this creates an electrical disequilibrium (uneven distribution of electrons) more
positive outside and more negatives inside; therefore there is no even amount to make it neutral: E.G. : 4 K in and 4 Na out=
neutral. But with 4 K in and 5 Na out= electrical disequilibrium, no equal net charge.
the input of energy to transpor t ions across the membrane creates an electr ical gradient (the difference in net charge
between 2 ions) I’m assuming its the kind of energy to make it go against its own gradient and chemical gradient goes along with
combination of electrical and chemical gradient is called an electrochemical gradient.
electrical gradient is the difference in charge between the intracellular and extracellular. It is also called RESTING
A voltmeter is used to measure the electrical difference (membrane potential versus time) between the inside of the cell and the
outside of the cell in volts or microvolt. The reference electrode is placed in the extracellular fluid (in the diagram, it is in a
saline bath). It is assigned as the ground state or can be said as 0mv.
recording electrode= inside the cell.
K is mostly responsible for RMP.
When a K leak channel is in a cell membrane, it makes it possible for k to leak out of the cell. This makes it possible for k to
leave since the membrane is impermeable to ions. Since there is no K in the extracellular fluid, it is so easy for it to go outside of
the cell (concentration gradient). Since the K and proteins are attracted to each other, due to charge, the proteins want to leave the
cell as well. However, they cant follow because the cell membrane is impermeable to them and because they are big.
•now, k is going smoothly along its chemical gradient, but by continuing to go along with it, its going to eventually create an
electrical gradient. What does this mean? Because opposite charges attract each other, the negative proteins are going to attract
the K ions back into the cell, its calling in. its E-ion will be -90mV. In order to prevent it from flux.
concentration gradient is out and electrical gradient is going into the cell.
How does K stop moving then? The electr ical forces attracting K into the cell becomes equal to the magnitude to the chemical
concentration gradient driving K out of the cell down its concentration gradient now this is the point where K stops moving
across the membrane.
Rate at which K ions move out of the cell down the concentration gradient = to the rate at which k ions move into the cell down
the electr ical gradient.
Eion= means its permeable to one ion, the membrane potential that exactly opposes the concentration gradient of an ion. The
equilibrium potential for any ion at 37 degrees Celsius (human body temp) can be calculated by using the NERNST Equation.
Nernst equation is used to measure Equilibrium potential of an ion.
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