While most current biological research focuses on molecular, biochemical aspects of cell function, we are interested in the mechanical properties of cells and tissue and their importance for biological function. The mechanical strength of cells is largely determined by the cytoskeleton, an internal polymer hybrid network intricately regulated by many signaling pathways. This cytoskeleton evolves during physiological changes, such as differentiation, is involved in many cellular functions, such as migration, and is characteristically altered in pathologies, including cancer or inflammation. We can exploit the deformability of the cytoskeleton as a link between molecular structure and biological function to sensitively monitor these functional changes using an optical stretcher. Our findings suggest the use of cell compliance as an integral, inherent cell marker obviating the need for external markers or special preparation. Further, also the mechanical properties of biological tissues are increasingly being recognized as important because cells measure and respond to the mechanics of their environment. We are investigating this mechanosensitivity of neurons and glial cells in the context of development and pathologies of the central nervous system. This research could lead to novel therapeutic approaches in traumatic injuries to the CNS and neurodegenerative disorders.