ioo TEXT-BOOK OF PHYSIOLOGY 



inhibitors. The nerves which pass to that specialized part of the 

 vascular apparatus, the heart, transmit nerve impulses which on the 

 one hand accelerate its rate or augment its force, and on the other hand 

 inhibit or retard its rate and diminish its force. For this reason they 

 are termed cardiac nerves, one set of which is known as cardio-accelera- 

 tor and cardio-augmentor, the other as cardio-inhibitor nerves. 



4. Visceral or viscero-motor nerves, those which transmit nerve impulses to 



the muscle walls of the viscera and change in one direction or another 

 the degree of their contraction. Those which increase or augment the 

 contraction are known as viscero-augmentor, while those which decrease 

 or inhibit the contraction, are known as viscero-inhibitor nerves. 



5. Hair bulb or pilo-motor nerves, those which transmit nerve impulses to the 



muscle-fibers which cause an erection of the hairs. 

 Of the foregoing nerves the skeletal-muscle or motor nerves alone pass 

 directly to the muscle. The gland, the vascular and the visceral nerves, all 

 terminate at a variable distance from the peripheral organ around a local 

 sympathetic ganglion, which in turn is connected with the peripheral organ. 

 The former are termed pre-ganglionic. The latter post-ganglionic fibers. 

 (See Fig. 13.) 



The Afferent Nerves. The afferent nerves may also be classified, in ac- 

 cordance with their distribution and the character of the sensations or other 

 modes of nerve activity to which they give rise, into several groups, as follows: 

 A.^Tegumentary nerves, comprising those distributed to skin, mucous mem- 

 branes and sense organs and which transmit nerve impulses from the 

 periphery to the nerve centers. They may be divided into reflex and 

 sensorifacient nerves. 



1. Reflex nerves, those which transmit nerve impulses to the spinal 

 cord and medulla oblongata, where they give rise to different 

 modes of nerve activity. They may be divided into: 



a. Reflex excitator nerves, which transmit nerve impulses which 

 cause an excitation of nerve centers and in consequence in- 

 creased activity of peripheral organs, e.g., skeletal muscles, 

 glands, blood-vessels and viscera. 



b. Reflex inhibitor nerves, which transmit nerve impulses which 

 cause an inhibition of nerve centers and in consequence, 

 decreased activity of the peripheral organs. It is quite prob- 

 able that one and the same nerve may subserve both sensation 

 and reflex action, owing to the collateral branches which are 

 given off from the afferent roots as they ascend the posterior 

 column of the cord. 



2. Sensorifacient nerves, those which transmit nerve impulses to the 

 brain where they give rise to conscious sensations. They may be 

 subdivided into: 



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

 gustatory, tactile, thermal, pain, pressure which give rise to 

 correspondingly named sensations. 



b. Nerves of general sense e.g., the visceral afferent nerves 

 those which give rise normally to vague and scarcely perceptible 

 sensations, such as the general sensations of well-being or dis- 

 comfort, hunger, thirst, fatigue, sex, want of air, etc. 



