Part Reactions of the Hidden Machinery
There are the cog-wheels, in human machinery that connect the receptors of stimuli, from outside, with the muscles and glands that can finally be seen responding to that stimulus. The entire human nervous system is customarily divided, for convenience of description, into two parts, the central nervous system and the peripheral, or outlying, groups of neurones. The cord retains the primitive segmentation found in lower forms of life and controls the reflex reactions of the body. The cerebral cortex controls the activities of the rest of the body. The visceral efferent fibres passing to these same organs from the medulla, constrict the arteries, depress the heart action, increase the contractions of the stomach, and constrict the bronchii. The autonomic nervous system consists of a series of ganglionic cells lying just outside the spinal cord.