Though similar to tendons, ligaments connect bone to bone and help to stabilize joints they surround. They are composed mostly of long, stringy collagen fibers that create bands of tough, fibrous connective tissue.
An electron is a negatively charged subatomic particle. It can be either free (not attached to any atom), or bound to the nucleus of an atom. Electrons in atoms exist in spherical shells of various radii, representing energy levels. The larger the spherical shell, the higher the energy contained in the electron.
A proton is a positively charged particle located in the nucleus of an atom. An electron has $\frac{1}{1836}$ times the mass of a proton, but an equal and opposite negative charge. An elementary charge -- that of a proton or electron -- is approximately equal to 1.6Ã10-19Coulombs. Unlike protons, electrons can move from atom to atom. If an atom has an equal number of protons and electrons, its net charge is 0. If it gains an extra electron, it becomes negatively charged and is known as an anion.