Nerve, in anatomy, denotes certain white, round, delicate substances, similar to cords, which proceed from the brain or spinal marrow, and are divided into numerous smaller fibres or branches, that are dispersed throughout the body.
The nerves have been supposed to contain a very subtle fluid,which may be either of a magnetic or electrical nature ; and though the nervous fibrils, when examined with the microscope, appear to be solid bodies, yet they probably conduct a very subtle fluid by means of their interstices. Thus, they are the immediate instruments of sensation, and are indispensably necessary for the continuance of muscular motion.
Wounds are the chief accidents to which the nerves are liable: but as the former require immediate chirurgical assistance, we snall only remark, that the nerves of several animals are larger than those of man ; though, possessing a very-inferior degree of sensation. Indeed, the mental capacities of beings are by no means proportioned to the size of their nerves, proceeding from the brain :—amphibious animals, for instance, possess strong nerves, in proportion to the diminutive size of their brain ; and are nevertheless uncommonly dull of apprehension, and even insensible. On the contrary, children affected with the rickets, and persons of lean habits, have a large brain, and very delicate nerves ; yet they possess not only a high degree of mental vigour, but likewise uncommon acuteness in the perceptions of sense.
Nervous diseases are supposed to arise from an increased sensibility of the nerves, under the influence of some stimulus ; and are principally distinguished by their predominant painful symptoms ; for instance, violent head-ach, tooth-ach, face-ach, etc. Hence the absurdity of classing almost every complaint, the origin of which is not obvious, among the nervous, and to misapply this term to disorders of a very different nature, such as general weakness, occasioned by muscular relaxation, or mental imbecility, peevishness, want of resolution, etc. if connected with bodily causes, however distant or concealed.