308 



THE INTERNAL ENVIRONMENT OF THE BODY 



Part III 



encephalograms) show that brain cells are more or less continuously active. 

 This is clearly demonstrated by a frog's brain, which when taken from the 

 body and kept alive, will continue to generate electrical waves for some hours. 

 All brain waves are so feeble that they can be recorded only after being 

 received by a very sensitive apparatus and magnified millions of times. They 

 occur rhythmically, and sleep is the only normal condition in which they 

 are much altered. During sleep, the records show waves that are slower and 

 wider, sometimes broken by irregularities, beheved to be caused by dreams 

 (Fig. 16.23). Brain diseases change the brain waves, and epilepsy can be 

 diagnosed by characteristic wave patterns. 



Sleep 



The average individual spends from a quarter to a third of his lifetime in 

 sleep. All observations on sleep have ended in the conclusion that animals 

 cannot live without it. However, the actual nature of sleep is unknown and 

 this is especially true of the part played in it by the nervous system. 



ExciTeo - 



RCLAXCD 



DROWSY 

 ASLEEP 



DEEP SLEEP 



I SEC 



so;xv. 



Fig. 16.23. Sleep and excitement in the human brain. Records of electrical 

 waves produced in the normal human brain. Excitement is characterized by very 

 frequent waves and sleep by irregular, less frequent ones. In the (upper) sleep 

 record there was a "sleep spindle" of frequent waves every 14 seconds. (After 

 Jasper. From Penfield and Erickson: Epilepsy and Cerebral Localization. Spring- 

 field, 111., Charles C Thomas, 1941.) 



