Calcium ions are one of the key mediators in the cell. Their action takes place, inter alia, through the calcium-binding proteins. Among the calcium-binding proteins are a growing number of discovered in the past ten years, protein motif "EF-hand" which form the so-called family. Sensors neuronal calcium (NCS, Neuronal Calcium Sensors). It belong to, inter alia: rekoweryny, frekweniny protein GCAP, VILIP protein. Their common feature is the presence of a characteristic structure and in certain nerve cells, which suggests that there remain a precise function.

The pineal gland ? located in the vertebrate brain endocrine gland ? has a number of common features of the retina of the eye. Both organs have developed as pouches diencephalon , act as photoreceptive and produce melatonin in a light-dependent manner . In contrast to the retina , pineal gland has undergone significant evolutionary changes and forming it pinealocytes differ in vertebrates both construction and function .