962 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



rect stimulation Wang & Brown (167) found that 

 excitation of the ventromedial Inilhar reticular forma- 

 tion, the cerebellar anterior lobe, the caudate nucleus 

 and the frontal cerebral cortex inhibits the galvanic 

 skin reflex. The reticular formation has the lowest 

 threshold of stimulation and the greatest inhibitory 

 effect. 



Another approach to brain-stem facilitation of 

 autonomic acti\it\- has been used by Glasser (63) who 

 found that midpontile decerebration, in cats with 

 sectioned vagi and with carotids tied, produces an 

 increase in arterial pressure and heart rate as well as 

 apneusis and decerebrate rigidity. This increase in 

 cardioxascular activity is attributed to facilitation by 

 the reticular formation. 



It also appears likely that some autonomic mecha- 

 nisms may participate in the bulbar facilitation of 

 somatic reflex activity. Bach (10) finds that stimula- 

 tion of the bulbar reticular facilitatory mechanism 

 results in liberation of epinephrine and activation of 

 the sympathetic nerve supply 10 the limb in\ol\ed. It 

 is not certain that the facilitation so produced is the 

 only mechanism w-hich acts at the site of the reflex arc 

 within the cord. 



A converse effect has been described by Dell and 

 his co-workers (44) who have found activation of the 

 upper midbrain reticular formation by epinephrine 

 which in turn leads to a generalized activation of the 

 upper portion of the brain. This humoral mechanism 

 may be important for arousal from sleep. There is 

 also evidence that the ' sympathetic nervous system 

 acts on facilitatorv and inhibitory functions of the 

 reticular formation in motor activity, and that afferent 

 impulses from the pressor receptors of the carotid 

 sinus may have inhibitory eflfects here. It has been 

 shown that the midbrain and hypothalamus contain 

 significant amounts of sympathin (162). Indeed, these 

 regions contain the richest supply of sympathin in the 

 entire brain of the dog, and Dell presents arguments 

 for an adrenergic type of transmission in this part of 

 the iirain. 



Dell points to the regulation of blood sugar as an 

 example of autonomic neurohormonal interaction 

 which is ba.sed on the existence of reserves of glycogen 

 in the li\er and muscles. When these reserves are 

 diminished, there is an augmentation of the secretion 

 of epinephrine and increase in its level in the blood. 

 As a result the following events occur ; wakening, aug- 

 mentation of muscular activity even to the point of 

 hyperactivity, intensification of sensory attention so 

 that the animal develops a drive to satisfy its need for 

 food. Fundamental mechanisms for the transforma- 

 tion of organic needs into behavior thus appear to 



be represented in this portion of the brain. Another 

 chemical feed-back mechanism may be constituted 

 by the fact that any sensory mechanism which is 

 concerned with the arousal of the emotional response 

 may feed into the reticular formation, including of 

 course the hypothalamus, and provoke discharges 

 which bring about the release of epinephrine and nor- 

 epinephrine. This in turn, acting on the reticular 

 formation, can augment and prolong the actis'ity of 

 the elements of this system up to the time when the 

 circulating hormone has been destroyed. As Dell 

 points out, this may offer some explanation as to why 

 it is usually \ery difficult to arrest or confine an emo- 

 tional state. 



Altiiougii the miclljrain is not usualh' held to be of 

 particular importance in the autonomic scheme, 

 aside from elements in the oculomotor and perhaps 

 the trigeminal complexes, and aside from the some- 

 what indefinite centers controlling tonus in the 

 rectum and bladder, we ha\e seen that this area 

 besides its importance as a transmitter of autonomic 

 impulses may plav a role in autonomic integration. 

 Part of this role is dependent upon hormonal influ- 

 ences. 



.•\UTONOMIC FUNCTIONS OF OCULOMOTOR NERVE. It is 



usually held that the preganglionic fibers for the 

 innersation of the constrictor muscle of the pupil and 

 of the ciliary muscle originate in the nucleus of 

 Edinger and Westphal which overlies the main 

 oculomotor nucleus, and that these fibers enter the 

 oculomotor ner\e and terminate in the appropriate 

 eye muscles. According to Olszewsky & Baxter (128), 

 however, the evidence that these fibers originate in 

 the Edinger-VVestphal nucleus is relatively scant. 



Beside the \isual afferent influences which bring 

 about the pupillary light and convergence reflexes, 

 afferent impulses of extraocular origin play an impor- 

 tant role in control of the pupil. Thus pupillary dilata- 

 tion occurs in response to noxious stimulation and 

 emotional excitement. This is in part due to activa- 

 tion of dilator pupillae muscles through the cervical 

 sympathetic. However, there is evidence, originally 

 advanced !)>• Ur\- & Gellhorn (60), that there is some 

 central inhibition of the pupilloconstrictor mecha- 

 nism. 



DIENCEPH.^LI^ .AUTONOMIC MECH.ANISMS 



The modern student of neurophysiology is all too 

 aware that there is a region called the hypothalamus 

 which, he has been led to believe, plays a key role in 



