Nerve fibres of the parasympathetic nervous system arise from the central nervous system. Specific nerves include several cranial nerves, specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve. Three spinal nerves in the sacrum (S2-4) also act as parasympathetic nerves.
The word longevity is sometimes used as a synonym for life expectancy in demography - however, the term longevity is sometimes meant to refer only to especially long-lived members of a population, whereas life expectancy is always defined statistically as the average number of years remaining at a given age.
Since four electrons are shared between two atoms in a double bond, more energy is required to break the bonded atoms apart compared to a single bond. Breaking a double bond between oxygen atoms requires three times the energy necessary to break a single bond between oxygen atoms. The same is true for nitrogen. What makes a double bond stronger also makes it shorter. The average bond length for a carbon double bonded to another carbon is 13% shorter than that of two single bonded carbons.