Mention has been made of some of these cells’
characteristic functional properties, their metabolic activities and power of
growth.
By these two properties then cell is
activity. When a cell is stimulated either by chemical, physical, mechanical,
or nervous means, the cell responds; it may contract as does a muscle cell
(fiber); it may produce a secretion, as do the cell of the stomach, pancreas,
and other organs and glands; or it may conduct an impulse, as in the case of
the nerve cell. This last is the best example of cell conductivities as a nerve
impulse generated by the stimulation of a nerve cell may be conducted for a
considerable distance, a yard or more, according to the length of the nerve
fiber. But in all case a stimulus which excites a cell to action is conducted
along the entire length, from end to end of the cell.
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