An elongated cell, part of the nervous
system, that transmits electrical impulses. A
nerve impulse is a travelling wave of
chemical and electrical changes that affects
the surface membrane of the nerve fibre.
Sequential changes in the permeability of the
membrane to positive sodium (Na^+) ions and
potassium (K^+) ions, produce electrical
signals called action potentials. Impulses
are received by the cell body and passed, as
a pulse of electric charge, along the axon.
At the far end of the axon, the impulse
triggers the release of chemical
neurotransmitters across a synapse
(junction), thereby stimulating another nerve
cell or the action of an effector organ (for
example, a muscle). Nerve impulses travel
quickly, in humans as fast as 160 m/525 ft
per second along a nerve cell.