Chapter XI

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Nerves are bundles of fibers made of linked (i.e., nerve cells) that transmit electrical and chemical signals between the central nervous system and the body tissues. “Nerve” comes from the second-declension Latin noun , which is etymologically related to neuron, the Greek word for “nerve,” and also “bowstring.” Small bundles of nerve fibers are known as fasciculi, “little ” (fasciculi is a plural form of the -declension noun fasciculus, a diminutive derived from the base fasci-). An individual neuron contains a cell body (with nucleus and surrounding cytoplasm), from which extend short radiating processes called “.” These “tree-like” structures make up most of the receptive surface of a neuron. (Grk. “axis”) describes the single, long process that carries signals away from the cell body and splits into branches (axon terminals) that end in the (Grk. “joining together”), the site at which an impulse is transmitted from one neuron to another, or to an organ.

Many nerves get their name from their location. The , tibial, and intercostal nerves are found, as you could guess, in the area of the cheek, leg, and respectively. Likewise the nerve runs vertically down the calf of the leg (Lat. “calf”), and the nerve, which supplies the external genitalia of both sexes, gets its name from the Latin for “genitals” (lit. “things which require modesty”). The nerve starts at the neck and passes down through the heart and lungs to reach the diaphragm, the structure that gives it its name (the Greek word associated with this nerve was used to refer to the midriff area, which in some contexts was viewed as the seat of various mental and emotional processes, hence the common translation of “heart” or “mind”; see p. 281). The nerve is also named after its location, though with a linguistic twist that makes the connection more difficult to discern, as it is a corruption of “ischiadic,” which itself comes from ischium, a Greek word that is filtered through Latin (see p. 21).

A couple of other nerves have more interesting names. The bundle of nerves and nerve roots at the base of the spinal cord, for example, is known as the cauda equina, a term which you might be able to identify on the basis of what you have learned so far. You learned in Chapter IV that caud- means “,” and you may be able to guess the second word from your knowledge of the English “equestrian” or “equine.” The phrase is composed of a -declension noun cauda (fem. nom. sing.) and the adjective equina, which combine to mean "horse’s tail,” so called because of its tail-like extension from the spinal cord. Other nerves earn nicknames because of a particularly prominent characteristic. The nerve is so called because it innervates—i.e., transmits nerve signals to and from—the lung and stomach, but it is also called the “ nerve” because of its meandering path from the medulla through the jugular foramen into the carotid sheath and down below the head into the neck, chest, and abdomen—a fitting title, as this word is Latin for “wandering.”