350
The Body Electric
Galvanotaxis: The movement of a living organism toward or away from a
source of electric current.
Gene: A portion of a DNA molecule structured so as to produce a specific effect
in the cell.
Gene expression: Specific structure and activity of a cell in response to a group
of genes coded for such activity. For example, genes coded for muscle
cause a primitive cell to assume the structure and function of a muscle
cell.
Glia: A tissue composed of a variety of cells, mostly glial cells, that makes up
most of the nervous system. These cells have been considered nonneural in
the sense that they cannot produce nerve impulses. Therefore they have
been thought unable to transmit information, rather having protective and
nutritive roles for the nerve cells proper. This concept is changing. It is
now known that glial cells have electrical properties that, while not the
same as nerve impulse transmission, enable them to play a role in com-
munication in the body.
Hertz: Cycles per second, the unit for measuring the vibratory rate of elec-
tromagnetic radiation. Named for Heinrich Hertz, German physicist who
made the first experimental discovery of radio waves in 1888.
Homeostasis: The ability of living organisms to maintain a constant "internal
environment." For example, the human body maintains a constant amount
of dissolved oxygen in the blood at all times by means of various mecha-
nisms that sense the oxygen level and increase or decrease the breathing
rate.
In vitro: An experiment done in a glass dish on part of a living organism.
In vivo: An experiment done on an intact, whole organism.
Magnetosphere: The area around the earth in which the planet's magnetic field
exerts a stronger influence than the solar or interplanetary magnetic field.
It extends some 30,000 to 50,000 miles from the earth's surface. A prom-
inent feature of the magnetosphere is the Van Allen belts, areas of charged
particles trapped by the earth's magnetic field.
Magnetotactic: Active movement toward a magnetic pole.
Mesoderm: One of three primary tissue layers in the embryo, which develop as
differentiation (cell specialization) begins. It becomes the muscular and
circulatory system in the adult.
Mitosis: Cell division. Actual division takes only a few minutes but must be
preceded by a much longer period during which preparatory events, such
as duplication of DNA,
take place.
The entire process generally takes
about one clay.
Neoblast: An unspecialized embryonic cell retained in the adult bodies of cer-
tain primitive animals and called to the site of an injury to take part in
regenerative healing.