284 HUMAN ANATOMY. 



A neuron is the term given to a nerve-cell with its axon, or 

 axis-cylinder process, and its dendritic processes. Each neuron 

 is a distinct and separate unit. 



(c) Neuroglia, the supporting framework of nerve-tissue, 

 is made up of a matrix of delicate, fibrillar net-work and small 

 neuroglia cells, and forms an imbedding substance for the other 

 elements. 



Nerves are round, white, shining cords, belonging either 

 to the cerebro-spinal or the sympathetic systems. They are made 

 up of bundles of nerve-fibres held together by fibro-connective 

 tissue, the epineurium. The individual fibres are held together 

 within the bundles by connective tissue, the endoneurium. 



The nerve-fibres have a twofold function sensory and 

 motor. 



Sensory, or afferent, transmit impressions from the periph- 

 ery to the centres. 



Motor, or efferent, transmit impressions from the centres to 

 the periphery. 



Ganglia form independent nerve-centres, similar to but less 

 complex than the brain. They are connected with some of the 

 cranial nerves, all of the spinal nerves, and form an important 

 part of the sympathetic system. 



Terminations. The motor nerves end in the voluntary and 

 involuntary muscles, tne former having special endings called 

 the motorial end plates. 



The sensory nerves terminate in the peripheral organs, to 

 which they are distributed by first becoming non-medullated, 

 and then dividing and joining one another to form a minute 

 plexus or by means of one of the three special endings, called 

 "peripheral end organs": (1) tactile corpuscles of Wagner; (2) 

 end bulbs of Krause; or (3) the Pacinian corpuscles. 



CEREBRO-SPINAL AXIS. 



The cerebro-spinal axis is divided into two grand divi- 

 sions : 



The encephalon, or brain, and spinal cord. 



Membranes of the Brain. The membranes of the brain are 

 three dura mater, arachnoid, and pia mater. 



Dura mater is a dense, white, fibrous membrane lining the 

 interior of the skull, and forming its internal periosteum, to 

 which it is adherent at the sutures. 



It contains the sinuses or venous channels (already de- 

 scribed), and forms three partitions for the support of the 

 brain the falx cerebri, falx cerebelli, and tentorium. 



