Lowly Origins

This chapter, “Lowly Origins,” examines the evolution of the nervous system and its implications for clinical neurology. Topics include peripheral nerve anatomy, extraocular muscles, and physiologic circuits related to respiration. Human neuroanatomy and neurologic disease carry a record of our vertebrate ancestors, and neurology is more understandable when the clinician is attuned to our ancient neurological circuits. The extraocular muscles are a prime example. Although the extraocular muscles have changed their orientation to the axis of the eye, and although not all of these muscles are as important as they once were, these muscles of the human eye have otherwise changed little from those of the shark. They remain similar in appearance and consistent in innervation. They are the best conserved muscles in all of vertebrate evolution. The development of limbs, loss of gills, assumption of bipedal locomotion, and development of a huge brain has had virtually no effect on them.