HISTOLOGY OF NERVE TISSUE 1 



1. Examine, with the low and with the high power, a prepared trans- 

 verse section through the spinal cord of the Frog or other Vertebrate. 

 Note : (a) the thin, outer covering (dura mater) ; (6) the rather shallow 

 indentation on the dorsal side (dorsal fissure) ; (c) the deeper indenta- 

 tion on the ventral side (ventral fissure) ; (rf) the outer layer (white 

 matter) largely composed of nerve fibers, and less compact than (e) the 

 inner material of the cord (gray matter) which contains (/) a large num- 

 ber of nerve cells, or neurons. In the center of the cord is (g) the small 

 cavity (central canal) which runs the entire length of the spinal cord. 

 If the section happens to pass through a spinal nerve, the (h) dorsal 

 and ventral roots may be seen connected with the gray matter. Make 

 a drawing of the section to show the structures as observed. 



2. Using the high power, focus directly on the large, irregularly shaped 

 motor nerve cells in the ventral portion of the gray matter on either 

 side of the cord. Note the large nucleus in each cell and the firril- 

 lated cytoplasm. Try to find a nerve cell which has been sectioned so 

 that it shows the long nerve process (axon) leading from it. Draw one 

 of the motor nerve cells, showing all details of structure as observed. 



3. Secure a small piece of a fresh nerve taken from an anaesthetized 

 Frog, place it on a slide in a drop or two of normal salt solution, and tear 

 it apart with dissecting needles. Mount and examine under the micro- 

 scope. Note that the nerve is composed of a number of fine, thread- 

 like fibers, each of which consists of (a) a delicate, external membrane 

 (neurilemma), (6) a thicker insulating layer (medullary sheath), and 

 (c) the central nerve fiber, or axon, which, as noted above, is a direct 

 continuation of the cytoplasm of a nerve cell. At intervals along each 

 fiber, there are breaks in the medullary sheath (nodes of ranvier), but 

 the neurilemma and the axon are continuous. Draw to show the struc- 

 ture as observed. 



iB. pp. 214-215. 



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