ii 4 TEXT-BOOK OF PHYSIOLOGY. 



the mechanism of their walls, a contraction (vaso-constrictors) 

 or dilatation (vaso-dilators) of the vessel. 



4. Inhibitory nerves, those conveying nerve impulses that cause a 



"sTowing or complete cessation of the rhythmic action of organs. 



5. Accelerator nerves, those conveying impulses that cause an increase 



in the rhythmic action of certain organs. 



The efferent nerves have been somewhat differently classified by 

 Gaskell as follows: 



1. Nerves to skeletal muscles. 



2. Nerves to vascular muscles. 



(a) Vaso-motor, i. e., vaso-constrictors; accelerators and aug- 

 mentors of the heart. 



(b) V (iso-inhibitory ^ i. e., vaso-dilators; and inhibitors of the 

 heart. 



3. Nerves of the visceral muscles. 



(a) Viscero-motor. 



(b) Viscero-inhibitory. 



4. Nerves to glands. 



The afferent nerves may also be classified, in accordance with 

 the character of the sensations or other modes of nerve activity to 

 which they give rise, into several groups, as follows : 



1. Sensorifacient nerves, those conveying nerve impulses that give 



rise in the brain to conscious sensations. They ma}' be sub- 

 divided into 



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

 tory, tactile, thermal, pain, pressure, muscle giving rise to 

 correspondingly named sensations. 



(b) Nerves of gener^ sense e. g., the visceral afferent nerves 



those which give rise normally to vague and scarcely percept- 

 ible sensations, such as the general sensations of well-being 

 or discomfort, hunger, thirst, fatigue, sex, want of air, etc. 



2. Rejlex nerves, those which convey nerve impulses tp^ 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 sense 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 



TnKibiting the activity of either nerve-centers or peripheral 

 organs. 



