A nerve cell which connects a receptor with an effector. The term is sometimes applied to hormones and the blood stream as well.Connector cells number in the millions and constitute the vast majority of neurons in the body. Connectors called interneurons are usually found between the sensory and motor fibers in the spinal cord (see Fig. 45, p. 1115), while other connector neurons go up to the brain and down to the rest of the body. These connections are usually rather simple. The cerebral cortex, on the other hand, contains an enormously complex network of connectors. In the early treatises on the nervous system, this network was compared to a telephone switchboard. Today scientists no longer picture it as a complicated relay system but compare it to an electronic computer, since the brain not only transmits impulses but also plays an active role in organizing and directing behavior (Hebb, 1949). See SPINAL CORD, CEREBRAL CORTEX. The blood stream and hormones are known as connectors because they, too, take an active part in integrating the functions of the organism. An overfatigued muscle will affect muscles in other regions of the body because chemical substances resulting from fatigue are distributed through the blood stream. Coordination also occurs through the circulation of hormones. Adrenal secretions released in an emergency situation bring about an entire pattern of responses that includes heightened blood pressure, increased clotting of blood, dilation of pupils of the eye, and tensions in the skeletal muscles. These functions justify the application of the term connector to both the hormones and the blood stream.