SPINAL CORD. 173 



therefore the channels by which the volitional nerve impulses are conducted 

 from the motor area of the cortex to the multipolar cells in the ventral cornua 

 of the gray matter of the spinal cord, and by them and their related nerves 

 transmitted to the muscles. 



Spino-encephalic, or Sensor Conduction. The nerve impulses that 

 are brought to the spinal cord by the afferent spinal nerve-fibers are trans- 

 mitted by afferent paths in the cord for the most part to the cortex of the 

 cerebrum where they are translated into conscious sensations. These 

 paths are therefore termed sensor. The sensor tract passes through the 

 cord, the medulla oblongata, the pons Varolii, the superior portion of the crus 

 cerebri, the posterior third of the posterior limb of the internal capsule, to 

 sensor perceptive areas in the cerebral cortex. The sensor pathway decus- 

 sates at all levels of the spinal cord and medulla, and therefore the sensibility 

 of each side of the body is associated with the opposite side of the brain. 



The paths for the nerve impulses that give rise to different sensations have 

 been variously located by different observers. The pathway for the im- 

 pulses that give rise to the sensations of temperature has been located in the 

 gray matter; the pathway for the impulses that give rise to the sensation of 

 pain has been located in Gower's tract; the pathway for tactile impressions 

 has been located in the posterior columns. 



Properties of the Spinal Cord. Irritation applied directly to the ventro- 

 lateral white columns produces muscular movements, but no pain; they are, 

 therefore, excitable, but insensible. 



The surface of the dorsal columns is not sensitive to direct irritation, 

 except near the origin of the dorsal roots. The sensibility is due, however, 

 not to its own proper fibers, but to the fibers of the dorsal root, which traverse 

 it. 



Division of the ventro-lateral columns abolishes all power of voluntary 

 movement in the lower extremities. 



Division of the dorsal column impairs the power of muscular coordination, 

 such as is witnessed in locomotor ataxia. 



The gray matter is probably both insensible and inexcitable under the 

 influence of direct stimulation. 



A transverse section of one lateral half of the cord produces 



1. On the same side, paralysis of voluntary motion, a relative or absolute 

 elevation of temperature, and an increased flow of blood in the paralyzed 

 parts; hyperesthesia, for the sense of contact, tickling, pain, and tempera- 

 ture. 



2. On the opposite side, complete anesthesia as regards contact, tickling, 

 and temperature in the parts corresponding to those which are paralyzed 



