34 



VETERINARY STUDIES 



Dendrites 



Cetl body 



branches (dendrites), over which impulses come to the cell body 

 from the axon of some other cell or from a terminal sense organ, 

 as a taste bud on the tongue or a tactile (sense of touch) 

 corpuscle in the skin, connective tissue, and blood vessels. The 

 function of a nerve center is to receive and dispose of impres- 

 sions which may be brought to it, to provide connection for nerve 



fibers, and in the case of the 

 forebrain to originate conscious 

 impulses. 



Some nerve fibers or axons are 

 composed of a central filament, 

 the axis cylinder, or axon, sur- 

 rounded by one or two protect- 

 ing sheaths ; others are composed 

 of the central filament only. 

 Nerve fibers conduct impulses 

 between the various tissues and 

 organs, and nerve centers. A 

 nerve fiber or axon then is a 

 long, very slender, white or 

 grayish thread, the extension of 

 a nerve cell. 



A nerve is composed of an 

 indefinite number of nerve fi- 

 bers supported within a com- 

 mon sheath. 



A nerve cell or neuron is an 



irregularly shaped microscopic 



cell, having a varying number 



of branches, one of which may 



continue to indefinite length as the axis cylinder or central 



filament previously mentioned. 



Nerve Fibers. — Classified according to function, nerve fibers 

 are either : motor, sensory, or special sense. Each of these 

 conveys but one certain impulse and in one direction only. 



Motor fibers are those which convey impulses to the muscles 

 and control muscular action; for example an electric shock, or 

 a pin prick of a motor nerve, causes the muscles which it sup- 

 plies to contract. 



Sensory fibers are those which convey impulses toward brain 

 centers and give only sensation to the structures to which they 



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Fig. 19. 



