NERVOUS SYSTEM. 2U l J 



of the disturbed physiological processes and conditions. To 

 diagnose diseases of the central nervous system requires a 

 knowledge of the location of the principal 

 functions 



Preliminary remarks on anatomy and physiology. All efferent 

 (motor) psychic (conscious and volitional) fibres originate in the 

 cortex of the cerebrum, and all sensory fibres and fibres of special 

 sense that conduct perceptible impulses terminate in the 

 cortex of the cerebrum. The voluntary motor fibres (psycho- 

 motor or cortico-muscular tracts, or simply pyramidal 

 tracts) course from the cortex, through the pons Varolii to 

 the anterior pyramids of the medulla oblongata. Here most of 

 these fibres cross over to the opposite side (motor decussation) 

 and go to the motor nerves of the extremities, through the lateral 

 columns of the spinal cord. A few fibres that do not decussate 

 as above described course along the anterior columns of the spinal 

 cord and gradually pass over to the other side like the rest, but 

 through the white commissure along the course of the cord. 



Hence destructive processes in one hem 

 isphere result in motor and sensory paraly- 

 sis on the opposite side of the body. 



The cerebral hemispheres are also the seat of all psychical ac- 

 tivities; they are the seat of thought, volition and sensation. Many 

 motor centers are also found in the cerebral cortex and 

 hence inflammatory, conditions of this region may be attended with 

 convulsive movements of the muscles. 



The midbrain (crura cerebri, corpora quadrigemini and optic 

 thalami) is the seat of the entire mechanism, harmony and equilib- 

 rium of all motions. Animals with both hemispheres removed, 

 but with the midbrain intact can retain their equilibrium under the 

 most varied conditions. Inflammatory irritation of the midbrain 

 produces involuntary movements. 



The cerebellum harmonizes or co-ordinates the movements of 

 the body by regulating the succession of muscular contractions. 



The spinal cord, besides conducting impulses to and from the 

 brain, contains reflex centers which, when stimulated by afferent 

 impulses, cause certain kinds of important movements (defense, 

 flight, etc). These movements are carried out independent of any 

 action on part of the brain, as is easily proved on decapitated ani- 

 mals or where the spinal cord has been cut through. The thus 

 isolated cord is as prompt as ever in producing reflex actions. The 

 lumbar cord is the special center for defecation and urination, 

 which also depend on reflex activity. 



To be able to recognize normal conditions as well as to 



determine the presence and seat of pathological changes in 



the central nervous system, observe the following points : 



