THE SPINAL CORD 563 



2. Reflex inhibition of spinal nerve-centers, in consequence of which 



there may be a decrease in the activities of skeletal muscles, glands, 

 blood-vessels, and viscera. 



3. Sensations of touch, temperature, pressure, and pain. 



4. Sensations of the duration and direction of muscle movements, of the 



resistance offered and of the position of the body or of its individual 

 parts (muscle sensations). 

 Division oj the dorsal root fibers is followed by: 



1. Loss of the power of exciting or inhibiting reflexly the activities of 



spinal nerve-centers and in consequence a loss of the power of 

 exciting or inhibiting the activities of peripheral organs. 



2. Loss of sensation in all parts to which they are distributed. 



The ventral roots are therefore efferent in function, transmitting nerve 

 impulses from the spinal cord to the peripheral organs which excite them to 

 activity. 



The dorsal roots are afferent in function, transmitting nerve impulses 

 from the general periphery to (a) the spinal cord where they excite its con- 

 tained nerve-centers to activity or to a more or less complete cessation of 

 activity (inhibition), and (b) to the cerebrum where they excite its centers 

 to activity with the development of sensations. 



The Relation of the Encephalic Nerves to the Encephalon. The 

 encephalic or cranial nerves consist of efferent and afferent fibers. The two 

 groups of fibers, however, are not comprised in a single nerve trunk as are 

 the corresponding fibers of the spinal nerves but pass for the most part to 

 their destinations as independent and distinct nerves. These nerves also 

 serve as a means of communication between the encephalon and the peripheral 

 organs. 



The efferent nerves taken collectively are also distributed to skeletal 

 muscles, glands, blood-vessels and viscera. 



The afferent nerves taken collectively are distributed to the skin, mucous 

 membrane and to specialized sense organs eye, ear, nose, tongue and skin. 

 Some of the afferent nerves contain efferent fibers which are distributed to 

 glands, blood-vessels and viscera. 



The origin and distribution of both efferent and afferent encephalic nerves 

 and the phenomena that follow their stimulation and divisions, and the func- 

 tions attributed to them will be fully considered in a subsequent chapter. 



