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Summary Physiology Chapter 5 - Membrane potentials and action potentials
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Summary of Physiology, Guyton and Hall, Chapter 5 Membrane potentials and action potentials.
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Physiology Chapter 5 - Membranepotentials and action potentials
Basic physics of membrane potentials
If a membrane would only be permeable to potassium ions, the normal mammalian
nerve fiber is about 94 millivolts, with negativity inside the fiber membrane. If the
membrane would only be permeable to sodium ions the nerve fiber is about +61
millivolts.
The magnitude of the Nernst potential is determined by the ratio of the
concentrations of that specific ion on the two sides of the membrane. The greater
the ratio, the greater the tendency for the ion to diffuse.
The sign of the potential is positive (+) if the ion diffusion from inside to outside is a
negative ion, and it is negative (-) if the ion is positive.
Equation of Nernst:
The Goldman (-Hodgkin-Katz) equation is used to calculate the diffusion potential
when the membrane is permeable to several different ions. The diffusion potential
depends on:
1. The polarity of the electrical charge of each ion
2. The permeability of the membrane (P) to each ion
3. The concentrations (C) of the respective ions on the inside (i) and
outside (o) of the membrane
Equation of Goldman-Hodgkin-Katz equation:
Four key points of membrane potentials:
1. Sodium, potassium and chloride ions are the most important ions
involved in the development of membrane potentials in nerve and muscle
fibers
2. The quantitative importance of each of the ions in determining the
voltage is proportional to the membrane permeability for that particular ion.
3. A positive ion concentration gradient from inside the membrane to the
outside causes electronegativity inside the membrane. (Positive ion going
outward)
4. The permeability of the sodium and potassium channels undergo rapid
changes during transmission of a nerve impulse, whereas the permeability of
the chloride channels does not change greatly during this process.
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