198 THE HUMAN BODY 



the emergency does no particular good, and when, as usually hap- 

 pens, the worry proves to have been needless, real harm. 



Emotion of satisfaction and contentment appear to manifest 

 themselves chiefly through the cranial autonomies. The sacral 

 autonomies control the activities of the generative organs. Their 

 emotional associations are for the most part those concerned with 

 reproduction. 



Neuro Muscular Fatigue. In a previous chapter (p. 101) mus- 

 cular fatigue was discussed, and the fact pointed out that under 

 ordinary circumstances the muscles are protected from fatigue by 

 precurring nervous fatigue. Twojgeneral locations are recognized 

 in the nervous system for the occurrence of fatigue. The first of 

 these is in the synapses. The delicate junctions between neuron 

 and neuron are Relieved to be highly susceptible to fatigue. In 

 terms of the prevailing theory we would say that the accumulation 

 of waste products at the synapses increases their resistance to the 

 passage of nervous impulses, and that the resulting hindrance to 

 nervous action constitutes fatigue. The second place of fatigue 

 is at the junctions between mator_nerves and the fibers of skeletal 

 muscle, These junctions consist of minute flat plates pressed 

 against the muscle-fibers and in which the nerve-fibers terminate. 

 They are known as motor end plates. There is ample proof that as 

 the result of continued excitation of a muscle the neuro muscular 

 junctions show a falling off in the ease with which impulses pass 

 through them to muscle-fibers. Synaptic fatigue and end plate 

 fatigue occur in such minute structures that we would be apt to 

 expect recovery to be rather rapid. As a matter of fact quick 

 recovery seems often to occur. It is a common experience to obtain 

 marked relief from fatigue by the briefest sort of a nap. Neverthe- 

 less, we are bound to recognize that although the feelings of fatigue 

 may be quickly dissipated actual restoration of the fatigued struc- 

 tures requires time. An ordinary night's rest is none too long for 

 recovery from nervous fatigue. In fact there is definite evidence 

 that under many conditions a single night's sleep does not suffice 

 for complete restoration. The almost universal and very valuable 

 habit of abstaining from ordinary duties one day in seven has its 

 physiological significance in the necessity of allowing at intervals a 

 longer period of restoration than the usual nightly ones, in order 

 that any fatigue which failed to be overcome in ordinary course 



