282 



ANATOMY AND PHYSIOLOGY 



Surgical note. The operation of lumbar puncture is for the purpose of 

 opening the dura and arachnoid and drawing off a certain quantity of 

 cerebrospinal fluid. 



SPINAL NERVES 



A spinal nerve is a collection of 

 motor and sensory fibers connected 

 with the spinal cord by two roots an 

 anterior root running from the motor 

 cells and tracts and a posterior root 

 running to the sensory tracts and cells. 



The two roots become imbedded 

 in one sheath at the intervertebral 

 foramen which transmits the nerve 

 from the spinal canal. 



Note. The "ganglion of the root" is a 

 small ganglion on the posterior root where the 

 true root fibers arise. 



The ganglion contains the cell-bodies of 

 fibers in the posterior roots; they are neces- 

 sary to the life of these roots. Two axons 

 belong to each ganglion cell; one becomes 

 part of a spinal nerve and ends in a sensitive 

 part of the body (skin, mucous membrane, 

 muscle tissue and lining of joints) ; the other 

 forms a fiber of the posterior root of the same 

 spinal nerve, and enters the cord to become 

 associated with cells of both posterior and 



FIG. 177. MEMBRANES OF SPI- 

 NAL CORD. 



i, Dura mater; 2, arachnoid; 

 3, post, root of nerve; 4, ant. 

 root 'of nerve, divided; 5, pia 

 mater; 6, linea splendens. 

 (Morris, after Ellis.} 



anterior horns. (The fibers of the anterior roots arise in the cells of the anterior 

 horns.) 



Clinical note. Since the spinal nerves contain both motor and sensory 

 fibers, they are called mixed nerves; and since the antero-lateral divisions of 

 the cord are motor tracts, and the postero-lateral divisions are sensory 

 tracts, we can understand how injury in one region will cause paralysis of 

 motion, and injury in the other will cause paralysis of sensation; while injury 

 of a mixed nerve will cause loss of both motion and sensation in the parts to 

 which the nerve belongs. 



The next chapter will present the spinal nerves. Certain 

 points of interest in connection with their structure and arrange- 

 ment are here indicated by way of preparation for the study. 



It will be noted that the spinal nerves are mixed nerves. That 

 is, they are connected with both ventral and dorsal columns of 

 the cord and contain both motor and sensory fibers until they have 



