For the performance of normal function, it is essential that every organ in the body not only receive an adequate supply of blood but also maintain constant communication with the central nervous system. This it does by means of afferent and efferent nerves, the former conveying information from the organ to the center and the latter carrying commands from headquarters to direct the activities of the peripheral structure. Through the afferent nerves the organism receives all impressions of the surrounding environment, and with the help of the efferent nerves suitable response is made by muscle, gland or other tissue.
The simplest reflex might be conceived of as involving the sensory end-organ, its fiber and cell in the spinal ganglion with a central branch arborizing around an anterior horn cell from which arises the motor nerve conveying an efferent impulse to distant muscle. However, the vast majority of reflexes are much