FUNCTIONS OF THE SPINAL CORD. Ill 



upon the calibre of the blood vessels. Complete destruction of the anterior 

 horns is followed by a paralysis of motion, degeneration of the anterior 

 roots, atrophy of muscles and bones and an abolition of reflex movements. 



2. As an Independent Nerve Centre. 



The spinal cord, by virtue of its containing ganglionic nerve matter, is 

 capable of transforming impressions made upon the centripetal nerves into 

 motor impulses, which are reflected outward through centrifugal nerves to 

 muscles, producing movements. These reflex movements taking place 

 through the gray matter, are independent of sensation and volition. 



The mechanism involved in every reflex act is a sentient surface, a 

 sensory nerve, a nerve centre, a motor nerve and muscle. 



The reflex excitability of the cord may be 



(i) Increased by disease of the lateral columns, the administration of 

 strychnia, and in frogs, by a separation of the cord from the brain, the 

 latter apparently exerting an inhibitory influence over the former and de- 

 pressing its reflex activity. 



2. Inhibited by destructive lesions of the cord, e. g., locomotor ataxia, 

 atrophy of the anterior cornuse, the administration of various drugs, and, in 

 the frog, by irritation of certain regions of the brain. When the cerebrum 

 alone is removed and the optic lobes stimulated, the time elapsing between 

 the application of an irritant to a sensory surface and the resulting move- 

 ment will be considerably prolonged. The optic lobes (Setchenow's 

 centre) apparently generating impulses which, descending the cord, retard 

 its reflex movements. 



All movements taking place through the nervous system are of this 

 reflex character, and may be divided into excito-motor, sensori-motor, and 

 ideo-motor. 



Classification of Reflex Movements. (Kiiss.) They may be divided 

 into four groups, according to the route through which the centripetal and 

 centrifugal impulses pass. 



1. Those normal reflex acts, e.g., deglutition, coughing, sneezing, walk- 

 ing, etc., pathological reflex acts, e. ., tetanus, vomiting, epilepsy, which 

 take place both centripetally and certrifugally, through spinal nerves. 



2. Reflex acts which take place in a centripetal direction through a 

 cerebro- spinal sensory nerve, and in a centrifugal direction through a sym- 

 pathetic motor nerve, usually a vasomotor nerve, e. g.> the normal reflex 

 acts, which give rise to most of the secretions, pallor and blushing of the 

 skin, certain movements of the iris, certain modifications in the beat of the 

 heart ; the pathological, which, on account of the difficulty in explaining 

 their production, are termed metastatic, e. g., ophthalmia, coryza, orchitis, 



