The nervous system (SN) is a complex system that acts to receive sensory information through nerves, transmit this information via the spinal cord and finally process it in the brain. The SN has three main roles: sensory input, processing and motor output. The SN can be divided into the central nervous system (composed of the brain and spinal cord), and the peripheral nervous system (composed of those nerves located outside the brain and spinal cord). Moreover, the extracellular fluid between the cells comprises four types of fluids: 1-intravascular fluid (blood), 2-interstitial fluid, 3--transcellular fluid and 4-cerebrospinal fluid. The excess of these fluids is absorbed by the capillaries of the lymphatic system.
