ii86 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



Fic. 15. Effect of diatheimic heating ol tlu- anterior hypothalamus on respiratory rate, shivering 

 intensity and ear-skin temperature in an unanesthetized dog. Heating is through a gold foil electrode 

 chronically placed under the hypothalamus. The dog is under relative cold stress as evidenced by 

 shivering and cutaneous vasoconstriction. Rectal and thoracic temperatures are also shown. Similar 

 heating of the posterior hypothalamus resulted in drovi'siness but did not intluence shivering or ear- 

 skin temperature. [From Hemingway et at. (loi).] 



vasodilatation and shivering. Sweating (165) may be 

 elicited by hypothalamic thermal stimulation (94). It 

 starts after a certain latency (26) as the skin has to 

 reach a temperature of about 34°C first (212) and 

 appears later than cutaneous vasodilatation and 

 polypnea (26). Local injections of calcium and mag- 

 nesium ions into the hypothalamus may suppress the 

 sweating response (96) ; on the other hand, such in- 

 jections also produce vasodilatation and fall of body 

 temperature (isO- 



Increased salivation accompanies panting esoked 

 by hypothalamic electrical stimulation. 



Pilomotor responses (210) may be evoked by elec- 

 trical stimulation of the hypothalamus in the un- 

 anesthetized animal, associated either with slowed 

 respiratory rate and few somatic phenomena (from 

 the anterior hypothalamus) or with increased re- 



spiratory rate, arterial pressure increase, and violent 

 somatic phenomena (from the posterior hypothala- 

 mus). These two different patterns may perhaps be 

 comparal)le to two naturally occurring reactions 

 where piloerection appears, the heat-preservation 

 reaction, and the rage-fear reaction. Piloerection can 

 occur in chronic decorticate animals and after anterior 

 hypothalamic destruction but not after posterior 

 hvpothalamic destruction. 



Shiveiirig 



Shi\ering consists of phasic skeletal muscular con- 

 tractions, in man becoming apparent first in the head 

 (masseter muscle), later in the arms, body and legs 

 (200). In extreme shivering, the oxygen uptake may 

 increase fivefold al)ove the resting value (i ). Shivering 



