who concluded nurves are two types- those of sensation and those of action.
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Nerves proved to be a fairly difficult part of the body to categorize. The origins of the word "nerve" -- initially a Greek word meaning tendon or sinew -- suggests a certain confusion between connective tissues and other, more subtle types of physical connections within the body. As late as the twelfth century, the Jewish philosopher Moses Maimonides observed: "One who is not knowledgeable in anatomy may mistake ligaments, tendons and chords for nerves." Nonetheless, ancient medical practitioners did understand that nerves served roughly two functions: movement and sensation. The question was how they operated and under the direction of which principal organ.
In the fourth century B. C., the Greek philosopher Aristotle believed firmly that the nerves were controlled by and originated in the heart because it was, in his interpretation, the first organ of the body and the seat of all motion and sensation. Not surprisingly, he was misled by his confusion between ligaments and nerves in drawing this conclusion. Six centuries later, the Roman physician Galen contradicted him, disparaging those "who know nothing of what is to be seen in dissection." Instead he concluded that the brain was the most important organ of the body, with the nerves emanating from it:
"I have shown in my book On the Teachings of Hippocrates and Plato that the source of the nerves, of all sensation, and of voluntary motion is the encephalon [the brain] and that the source of the arteries and of the innate heat is the heart."
Galen saw the spinal cord as an extension of the brain which carried sensation to the limbs. He believed that the nerves controlled the actions of muscles in the limbs, and that the two principal functions of the nervous system, sensation and motion, were governed by two different types of nerves: respectively soft and hard. He further insisted on a curious anatomical feature of the nerves, imagining them to be hollow tubes. Quite logically, he reasoned that this must be so in order for the animal spiritus, the body's principal source of vitality in his system, to circulate throughout the body. As the Renaissance illustration here indicates, the investigation of the nerves after Galen also became an inquiry into the effect of the brain on the body.
Medieval physicians, in agreement with Galen, believed nerves were offshoots of and controlled by the brain. The Islamic medical philosopher Avicenna wrote in the early eleventh century that "Nerves are one of the 'simple members' -- homogeneous, indivisible, the 'elementary tissues' (others include the bone, cartilage, tendons, ligaments, arteries, veins, membranes, and flesh)." He offered a more precise physical description of them -- "white, soft, pliant, difficult to tear." He and his contemporaries began to describe the complex and varied arrangements of nerves throughout the body, attempting to differentiate further their functions. In the Canon of Medicine, he observed: "Dryness in the nerves is the state which follows anger." Such statements suggest that Avicenna also believed the nerves to be entangled with and responsive to the emotions, yet another sign of their strong connections to the brain.
Slightly more than a century later, Master Nicolaus offered a more precise vocabulary to express the new complexity of the nervous system, discarding the terms "soft" and "hard" for the more familiar idea of sensory and motor nerves. He considered nerves subservient members of the brain that carried out the animal spirits to all members, endowing them with sensation and motion. He further differentiated their points of origin and termination.