8
Electric Activities
of the Cell
8.1 INTRODUCTION AND OVERVIEW
The electric activities of the cell constitute a major physical property of the cell that
allows a wide spectrum of functionalities such as messaging, cellular communications, timing of cellular activities, and even regulation of practically all biological
systems. The same electric properties of the cell are exploited for a number of biomedical signal measurements and imaging. Due to the importance of the cell’s
electric activities, we briefly explore these properties in this chapter.
It was not until the second half of the twentieth century that the theoretical explanation for electric potentials of the biological cells, in particular cellular membrane
potential, was described by Alan Lloyd Hodgkin and Andrew Fielding Huxley.
We start this chapter with the description of the chemical activities of the ions and
biological fluids and then formulate the mathematical formulation of the mechanism
under which these ions create a potential difference across the cell membrane.
8.2 ION TRANSPORT IN BIOLOGICAL CELLS
All animal tissues, such as muscles, nerves, and bones, are made up of individual
cells. These cells have liquids both outside the cell, which are called extracellular
fluid, and inside the cell, which are called intracellular fluid. The intracellular fluid
is also called the cell plasma. All biological liquids are mostly water with various
molecules, atoms, and ions suspended. The intracellular volume is separated from
the extracellular fluid by a cell membrane.
The cell membrane is constructed of a bimolecular lipid layer in between monomolecular protein layers on either side. A diagram of the cell membrane construction
is outlined in Figure 8.1. The cell membrane is semipermeable to small molecules
and ions. This means that only certain atoms, molecules, and ions are capable of
passing through the membrane.
Both the intracellular liquid and the extracellular fluid contain organic and inorganic molecules. All salts and acidic and alkaline chemical compositions when dissolved in water form electrically charged elements called ions. All the dissolved
charged atoms or molecular structures are distributed in the bodily liquids with different concentrations for the intracellular liquid and the extracellular liquid. These
concentrations are not constant, nor are they the same for all cells. The concentrations mentioned later in this chapter are averages for one particular species. Other
molecular chains are also dissolved, but not all molecules separate out into ions,
155
Electric Activities
of the Cell
8.1 INTRODUCTION AND OVERVIEW
The electric activities of the cell constitute a major physical property of the cell that
allows a wide spectrum of functionalities such as messaging, cellular communications, timing of cellular activities, and even regulation of practically all biological
systems. The same electric properties of the cell are exploited for a number of biomedical signal measurements and imaging. Due to the importance of the cell’s
electric activities, we briefly explore these properties in this chapter.
It was not until the second half of the twentieth century that the theoretical explanation for electric potentials of the biological cells, in particular cellular membrane
potential, was described by Alan Lloyd Hodgkin and Andrew Fielding Huxley.
We start this chapter with the description of the chemical activities of the ions and
biological fluids and then formulate the mathematical formulation of the mechanism
under which these ions create a potential difference across the cell membrane.
8.2 ION TRANSPORT IN BIOLOGICAL CELLS
All animal tissues, such as muscles, nerves, and bones, are made up of individual
cells. These cells have liquids both outside the cell, which are called extracellular
fluid, and inside the cell, which are called intracellular fluid. The intracellular fluid
is also called the cell plasma. All biological liquids are mostly water with various
molecules, atoms, and ions suspended. The intracellular volume is separated from
the extracellular fluid by a cell membrane.
The cell membrane is constructed of a bimolecular lipid layer in between monomolecular protein layers on either side. A diagram of the cell membrane construction
is outlined in Figure 8.1. The cell membrane is semipermeable to small molecules
and ions. This means that only certain atoms, molecules, and ions are capable of
passing through the membrane.
Both the intracellular liquid and the extracellular fluid contain organic and inorganic molecules. All salts and acidic and alkaline chemical compositions when dissolved in water form electrically charged elements called ions. All the dissolved
charged atoms or molecular structures are distributed in the bodily liquids with different concentrations for the intracellular liquid and the extracellular liquid. These
concentrations are not constant, nor are they the same for all cells. The concentrations mentioned later in this chapter are averages for one particular species. Other
molecular chains are also dissolved, but not all molecules separate out into ions,
155