PHYSIOLOGY OF NERVE TISSUE. 75 



1. Sensorifacient nerves, those conveying nerve impulses that give 

 rise in the brain to conscious sensations. They may be subdivided 

 into 



(a) Nerves of special sense e. g,, olfactory, optic, auditory, 

 gustatory, tactile, thermal, sensory, muscle those which give 

 rise to olfactory, optic, auditory, gustatory, tactile, thermic, 

 painful, and muscle sensations. 



(fr) Nerves of general sense e. g., the visceral afferent nerves 

 those which give rise normally to vague and scarcely per- 

 ceptible sensations, such as the general sensations of well- 

 being or discomfort, hunger, thirst, fatigue, sex, want of air, 

 etc. 



2. Reftex nerves, those which convey nerve impulses to the nerve 

 centers and cause a discharge and transmission of nerve impulses 

 outward through efferent nerves to muscles, glands, or blood- 

 vessels, and thus influence their activity. It is quite probable that 

 one and the same nerve may subserve both sensational and reflex 

 action, owing to the collateral branches which are given off from 

 the posterior roots as they ascend the posterior column of the cord. 



3. Inhibitor nerves, those which are capable reflexly of retarding or 

 inhibiting the activity of either nerve centers or peripheral organs. 



The Terminal Endings of Nerves. The efferent nerves, as they 

 approach their ultimate terminations, lose both the neurilemma and 

 medullary sheath. The axis-cylinder then divides into a number of 

 tufts or branches, which become directly and intimately connected 

 with the tissue cells. The particular mode of termination varies in 

 different situations. These terminations are generally spoken of as 

 " end organs." 



In the skeletal muscles the nerve-fiber loses both neurilemma and 

 myelin sheath at the point where it comes into contact with the 

 muscle-fiber. After penetrating the sarcolemma, the axis-cylinder 

 breaks up into small branches with bulbous extremities, forming the 

 so-called " motor plate," which rests directly on a disc of granular 

 material containing oval, vesicular nuclei. Each muscle-fiber pos- 

 sesses an individual end-plate. 



In the visceral muscles the terminal nerve-fibers form a plexus 

 around the muscle-fibers, and become organically connected with 

 them. In the glands the nerve fibers have been traced directly to their 

 secreting cells. The exact mode of their termination and connection 

 with the cells has not been clearly determined. 



