734 CENTERS IN THE SPINAL CORD. 



the paralyzed side, although not rarely the patellar reflex is increased. In case 

 of extensive cerebral disease, the reflexes are wanting on both sides if coma is 

 present at the same time, naturally also those of the anus and the bladder. 



In going to sleep there is transitory increase of the reflexes. In early sleep 

 the reflexes are enfeebled, the pupils small. During sound sleep the abdominal, 

 cremasteric, and patellar reflexes are wanting; tickling of the soles of the feet 

 and of the nose is effective only when of a certain degree of intensity. During 

 narcosis, as, for example, that induced by chloroform or morphin, the abdominal 

 reflex disappears first, then the conjunctival and the patellar reflex, and finally 

 the pupils become contracted. 



Abnormal increase in reflex activity is generally indicative of an increase in 

 the irritability of the reflex center. Abnormal irritability of the centripetal 

 nerves may also be the cause, while injury is a cause of inhibition. As the har- 

 monious execution of voluntary movements is largely controlled and regulated by 

 reflex activities, it will be readily understood that various derangements in those 

 movements are observed in the presence of disease of the spinal cord, as for ex- 

 ample the characteristic disorder of gait and of the movements of the hands in 

 cases of tabes dorsalis. 



CENTERS IN THE SPINAL CORD. 



The spinal cord contains, in various situations, centers that on reflex 

 stimulation permit the evolution of certain coordinated motor mechan- 

 isms. These centers are capable of preserving their activity even when 

 the spinal cord is separated from the medulla oblongata. Further, the 

 centers situated in the lower portion of the cord may remain active after 

 division of the upper portion, but in the normal body these spinal centers 

 are subordinate in their activity to other higher reflex centers in the 

 medulla oblongata. The centers may, therefore, be designated also 

 subordinate spinal centers. Further, the cerebrum may, partly through 

 the formation of conceptions, partly as the organ of the will, exert an 

 influence upon certain of the subordinate spinal centers by excitation or 

 inhibition of the reflexes. The following particulars are deserving of 

 mention : 



The center for dilatation of the pupil is situated in the lower cervical 

 portion, extending downward to the level of the first, second, and third 

 thoracic vertebras Budge's ciliospinal center. It is stimulated by 

 darkness. In man both pupils react simultaneously if the retina on one 

 side is darkened. Extirpation of this portion of the spinal cord on one 

 side is followed by contraction of the pupil on the same side. The motor 

 fibers, which have their trophic center in the same situation, pass through 

 the anterior roots of the upper three thoracic nerves, in the cat, into the 

 cervical sympathetic. 



In goats and cats this center, separated from the medulla oblongata, may 

 be stimulated directly by a state of the blood causing dyspnea, and likewise by 

 reflex stimulation of sensory nerves, for example the median, especially if the 

 irritability of the spinal cord has been increased by strychnin or atropin. After 

 total division of the upper portion of the cervical cord, subsequent section of the 

 sympathetic is followed by contraction of the pupils. The superior dilator center 

 situated in the medulla oblongata is described on p. 749. 



The center for defecation Budge's anospinal center. The centripetal 

 nerves are contained in the hemorrhoidal and inferior mesenteric plex- 

 uses. The center is situated at the level of the fifth (in the dog) or sixth 

 and seventh (in the rabbit) lumbar vertebrae. The centrifugal fibers 

 are derived from the pudendal plexus and pass to the sphincter muscle. 

 I he excitation of this center and its domination by the cerebrum are dis- 

 cussed on p. 285. 



