Physical aspects of medical science.

Physical aspects of medical science involve making physical models, physical approaches, and measurements by physical instruments. Among these, the physical approach is the most important for an exact elucidation of the physiological function of living materials. What is a physical approach? In the first step, the molecular mechanism of visual transduction will be demonstrated by considering the physical characteristics of diffusion of second messengers. In the next step, I will consider how frequency modulation-type impulse signaling is converted from amplitude modulation-type electric signaling. In the last section, I will discuss how impulse signaling (i.e., the train of action potentials) is processed by the neural network in the brain and eventually is recognized in the frontal cortex using near infrared spectroscopy. In order to obtain such a physical model of vision, many physical concepts are used, such as light reflex, energy transduction, diffusion of molecules, threshold, the Coulomb interaction, light absorption, and cluster analysis. Among them, the Coulomb interaction, light absorption, and diffusion of molecules are three essential keywords for the physical process.