NERVA 



4119 



NERVOUS SYSTEM 



In the year 68 the legions in Spain revolted, 

 declaring their leader, Galba, emperor, and the 

 insurrection spread to the Praetorian Guard. 

 Nero fled, but was overtaken, and committed 

 suicide. The detestation of him had been so 

 great that his name was erased from records 

 and monuments, his palace was torn down and 

 his statues were broken; but despite all this, 

 ami partly because of it, no one of the emperors 

 was more generally remembered. 



Consult Henderson's Life and Principate of the 

 i- or Nero ; Abbott's History of Nero. 



NER'VA, MARCUS COCCEIUS (39-98), the 

 thirteenth Roman emperor, the successor of 

 Domitian. He served as consul in the reign of 

 Titus and Vespasian, and in 96, on the death 

 of Domitian, was elected emperor by the Sen- 

 ate. His predecessor had left many abuses 

 which needed reforming, and Nerva proved 

 both wise and beneficent, lessening taxes, plac- 

 ing justice within the reach of all, and recalling 

 s. Fearing the strength of the Praetorian 

 rii, he associated with him in the rule Tra- 

 jan, commander of the legions in Germany, 

 who succeeded him. Nerva was deified by the 



a ft IT his death. 



NERVES, tmri'z, the organs of the nervous 



system which carry impulses from the brain 



and other nerve centers to all parts of the body, 



and from various parts of the body to the nerve 



re. Nerves conveying impulses to the 



nerve centers are called sensory or afferent 



nerves, and those conveying impulses from the 



re to various parts of the body, motor or 



efferent nerves. See NERVOUS SYSTEM, subhead 



>e*. 



NERVOUS, Mr'tWt, SYSTEM. If your 

 hand touches a hot object you instantly with- 

 it. If the point of the finest needle pricks 

 tlin mull tin -kin you sense the pain and locate 

 tin injury. 1 1 a friend calls to you from across 

 the street you respond. When you run your 

 heart beats faster, and you breathe more 

 quickly and ! -ply. I'nder all conditions your 

 body adapts itself to its surroundings, and the 

 organism which enables it to do this is the 

 ;s system. In thr lower animals the 

 is system is very simple and incomplete, 

 but as we pass from these to the higher form- 

 tnal life we tind the nervous system be- 

 ^ more and more complex, until in man 

 it reaches its highest development. 

 The nervous system consists of the brain and 

 rves, It i- often likened to a great tele- 

 -ystem. .11 corresponds to the 



nunge, the nerves to the con: 



wires and the networks of nerves or ganglions 

 to the local exchanges. The nerves carry im- 

 pressions (messages) from all parts of the body 

 to the brain, and the brain sends impulses 

 (commands) to all parts of the body; hence 

 this comparison gives a very good idea of how 

 our nervous system acts, with this exception 

 the telephone system must be set in action by 

 some outside force, while the brain has the 

 power to impel the nerves to action because it 

 is the seat of the mind. 



The nervous system is generally divided into 

 the cerebrospinal and the sympathetic systems. 

 The description of these will be better under- 

 stood if we first learn something about the 

 structure of nerve tissue. 



Structure of Nerve Tissue. Examination of 

 nerve tissue under a powerful microscope shows 

 it to consist of cells having a peculiar form. 

 They consist of a central portion or mass and 

 long, threadlike branches whose ends resemble 

 that of a string 

 that has been 

 frayed out. 

 These cells, to 

 which the name medullary 

 neurone is given, sheath, 

 compose the 

 nerve matter of 

 the system, so axis 

 that "the nervous cylinder, 

 system equals the 

 sum of its neu- 

 rones." Some of 

 the branches of nerve flber l 

 the neurones ex- 

 tend to remote 

 parts of the body, 

 but most of them 

 are short. The branches of different cells meet 

 and connect cell with cell and nerve with nerve. 

 Tli- i e are millions of these cells in the brain, 

 and tiny extend through it in all directions, 

 unit m;: eaeh center with its respective nerves 

 and one center with another. 



Nerves. Dissection of any animal reveals 

 numerous \\hite cords extending through the 

 muscles. These are nerves, or nerve trunks. 

 Each nerve consists of a central axis composed 

 of neurones, and enclosed in a sheath of white 

 fibrous tissue. A nerve tmnk consists of a bun- 

 dle of nerves and may be compared in its struc- 

 ture to a bundle of wires, each wire insulated 

 by being wound with thread. However, the 

 white fibers in the nerve run lengthwise in- 

 stead of being wound round the axis, as they 



nerve 

 trunK 



A NERVE 

 highly magnified. 



