Glossary 351
Neuroepidermal junction: A structure formed from the union of skin and
nerve fibers at the site of tissue loss in animals capable of regeneration. It
produces the specific electrical currents that bring about the subsequent
regeneration.
Neurohormone: A chemical produced by nerve cells that has effects on other
nerve cells or other parts of the body.
Neuron, or neurone: A nerve cell.
Neurotransmitter: A chemical used to carry the nerve impulse across the syn-
apse.
Osteoblast: A cell that forms bone by producing the specific type of collagen
that forms bone's underlying structure.
Osteogenesis: The formation of new bone, whether in embryogenesis,
postnatal development, or fracture healing.
PEMF: Pulsed electromagnetic field.
Periosteum: A layer of tough, fibrous collagen that surrounds each bone. It
contains cells that turn into osteoblasts during fracture healing.
Photoelectric material: A substance that changes light into electrical energy,
producing an electric current when light shines on it.
Piezoelectric material: A substance that changes mechanical stress into elec-
trical energy, producing an electrical current when deformed by pressure
or bending.
Potential: Another term for voltage, which may at times be limited to a volt-
age that exists without a current but is potentially able to cause a current
to flow if a circuit is completed.
Preformation: See Epigenesis.
Pyroelectric material: A substance that changes thermal energy into electrical
energy, producing an electric current when heated.
Redifferentiation: The process in which a previously mature cell that has de-
differentiated becomes a mature, specialized cell again. See also De-
differentiation , Differentiation .
Salamander: Any of a group of amphibians related to frogs but retaining a tail
throughout their lives. Salamanders live in water or moist environments.
Most are 2 to 3 inches long, but some grow to more than a foot in length.
Since salamanders are vertebrates, with an anatomy similar to ours, and
since they regenerate many parts of their bodies very well, they are the
animals most commonly used in regeneration research.
Schwann cells: The cells that surround all of the nerves outside of the brain
and spinal cord. See also Glia.
Sciatic nerve: The main nerve in the leg. It includes both motor nerve fibers
carrying
impulses to the leg muscles and sensory nerve fibers carrying
impulses to the brain.