Bell's later research on the anatomy of the brain resulted in an expanded version of his 1811 volume, entitled The Nervous System of the Human Body (1830). In these books Bell distinguished between sensory nerves that conduct impulses to the central nervous system and motor nerves that convey impulses from the brain or from other nerve centres to a peripheral organ of response. He announced that the anterior roots of the spinal nerves are motor in function, while the posterior roots are sensory—an observation that was experimentally confirmed and more fully elaborated 11 years later by François Magendie.