Medical Definition of PNEUMOTAXIC CENTER. : a neural center in the upper part of the pons that provides inhibitory impulses on inspiration and thereby prevents overdistension of the lungs and helps to maintain alternately recurrent inspiration and expiration. a neural center in the upper part of the pons that provides inhibitory impulses on inspiration and thereby prevents overdistension of the lungs and helps to maintain alternately recurrent inspiration and expiration.
Because of their uber-high stability, the noble gases are relatively unreactive. They have very high ionization energies and negligible electronegativities because they have no desire to gain or lose an electron.
Helium Helium is a colorless unreactive gas that is less dense that air. It belongs to the Noble gases which is the last group on the far right of the Periodic table. All of the Noble gases are chemically unreactive because they contain a complete number of electrons in the outer shell. Helium gas if often used in party balloons as it is lighter than air. Helium is also found in the sun and the stars where it is formed through a series of nuclear fusion reactions involving hydrogen.