COORDINATION 419 



drawn through simple reflex, but very that the speed of the nerve impulse would 



shortly certain parts of the brain are in- never be measured, and yet, just six years 



volved, even to the cortex where reasoning later, another scientist measured it very ac- 



and memory are possible. He may even con- curately; today any beginning student in 



sider. the advisability of wearing shoes, or physiology can duplicate the experiment 



the injury may be sufficiendy severe that with good precision. Such statements of 



he will remember the event for a long time, finality are dangerous, especially for a 



It seems that the impulses usually travel scientist, 



over certain paths but these can be altered Nerve impulses come to the brain from 



on a moment's notice and new paths are all over the body on afferent nerve fibers 



then followed. In other words, many con- like messages coming to the admiral of a 



ditions can determine the pathway over fleet. Just as the admiral must make deci- 



which an impulse may travel. There are sions diat will be sent by messages to var- 



many choices; which it chooses depends on ions parts of the fleet in order to accom- 



a large variety of circumstances. plish a certain goal, likewise, decisions are 



An illustration of how the reflex may be made in the brain and impulses are sent 



interrupted may be seen in the sneeze reflex, out over efferent nerve fibers to various 



Sneezing is caused by a stimulus originating parts of the body in order that certain 



in the nasal chambers; its ultimate fruition actions can be executed. Decisions are 



is an explosive expulsion of air through made for the most part in a routine manner, 



these chambers to dislodge the irritation, based on inherited principles or on experi- 



If, when the sneeze sensation begins, a sec- ence gained through having made simflar 



ond stimulation is set up by producing pres- decisions before. Most of the decisions are 



sure on the upper lip, the first pathway wfll made by the brain without breaking through 



be blocked. In other words, a new set of to consciousness, so that one is not aware 



conditions blocked the original reflex path- of most of its activity. This great center is 



way. Neurologists believed at one time that indispensable to the harmonious working 



certain pathways were set up not only in of the entire body. Aberrations in the brain, 



the cord but in the brain as well, and that so slight that they cannot be detected as 



each pathway was traversed by the impulse any physical change, produce such stark 



in exactly the same manner, thus making it changes in personality and emotional sta- 



"deeper" until it was well established. There bility that our society is forced to build 



seems to be no evidence for this idea and it special institutions such as prisons and asy- 



is now well known that the impulse may lums to house people so afflicted, 



travel over different pathways and may For a better understanding of the human 



never take the same course twice. Further- brain it is best to start with a lower verte- 



more, pathways may be employed by differ- brate type brain, which is relatively simple 



ent reflexes at different times. Which spe- in structure, and follow through to higher 



cific pathways are followed, and why, is one forms. In die discussion of invertebrates it 



of the most important problems in neurol- was shown that the obvious location for the 



ogy today. brain is in the animal's anterior end, which 



Brain. This part of the nervous system is is the part that arrives in any new environ- 

 the most complex and, of course, the most ment first. Among vertebrates the brain like- 

 difficult to understand. Only poorly under- wise has its beginnings and its subsequent 

 stood today, the brain will, perhaps, never development in the anterior end of the or- 

 be adequately comprehended, but to accept ganism, and as we progress from fishes to 

 such an attitude would be highly unscien- mammals (Fig. 16-18) it becomes increas- 

 tific. A great German scientist once said ingly prominent. 



