ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 



677 



>rd and the ganglion the peripheral stump remains entire, while the 

 mtral stump becomes atrophied. The ganglia of the posterior 

 >inal roots have, therefore, the office of trophic centers over the 

 isory nerves; the trophic centers for the motor nerves lie within 

 ie cord itself and are none other than the large, multipolar cells of 

 ie anterior horns. 



The anterior roots contain different centrifugal fibers motor 

 ibers, vasomotor fibers, sweat, and inhibitory fibers of the splanch- 

 dcs. The motor fibers take their origin in the cells of the anterior 

 lorns, while other centrifugal fibers are united to the cerebral cortex, 

 to the vasomotor fibers, they have their centers of origin in the 

 ledulla oblongata and cord to penetrate the anterior roots. They 

 >robably do this without entering into communication with the cells 

 >f the anterior horns. 



The posterior roots have centripetal reflex fibers. These leave 

 ie skin, muscles, and other organs; penetrate the spinal cord; and 

 ire in direct connection with the reflex centers located partly in the 

 >rd itself and partly in the medulla oblongata, pons, corpora quadri- 

 miina, cerebellum, and optic thalami. The other sensory and 

 ?nse fibers penetrate the cord by way of the posterior roots to 

 iscend toward the cerebral cortex. Here are received the several 

 mscious sensations: touch, pressure, temperature, pain, and mus- 

 jular sense. 



Path of Transmission of Voluntary Motion. Voluntary motor 

 excitation is transmitted from the cerebral cortex to the nerve-cells 

 }f the anterior horns by way of the anterior and lateral columns. 

 These columns, as a whole, do not participate in conduction, but only 

 the anterior pyramidal tracts of the anterior columns and the crossed 

 )yramidal tracts of the lateral columns. 



As the student knows, the crossed pyramidal tracts do not decus- 

 ite in the cord, but in the medulla oblongata. The direct pyramidal 

 tract does not decussate in the medulla, but in the spinal cord by way 

 )f the anterior commissure. 



When the spinal cord is completely severed the voluntary move- 

 Lents for all of the muscles below the point of section are absolutely 

 wlished. 



Path of Conscious Sensations. The sensations of touch and 

 mscular sense are transmitted by the posterior roots and traverse 

 ie posterior columns to the brain. 



Muscular sense is transmitted mainly by the posterior columns. 

 "he direct cerebellar tract, and probably Gowers's, also contain fibers 



