CHAPTEE XXV 



PHYSIOLOGY OF SPECIAL NERVES 



THE innervation of the different organs and organ systems has been dis- 

 cussed in connection with their functions,, hence in this chapter we need only 

 present the physiology of special nerves in the broadest outlines. For details 

 and controverted points, reference must be made to the previous chapters 

 of this book, and for the purely anatomical data to the text-books of anatomy. 



1. THE CRANIAL NERVES 



I. The olfactory, or the nerve of smell (cf. page 486). 



II. The optic, or the nerve of vision (cf. page 508), contains not only 

 afferent but efferent fibers. 



III. The oculomotor, or the common nerve of the eye muscles, innervates 

 the levator palpebrae superioris, the superior, inferior and internal recti, the 

 inferior oblique, the ciliary muscle or the muscle of accommodation (cf. page 

 532) and the sphincter of the pupil (cf. page 528). 



IV. The trochlearis, or patheticus, innervates only the superior oblique 

 muscle of the eye. 



V. The trigeminal, or trifacial, contains both afferent and efferent fibers. 

 The efferent fibers innervate the jaw muscles (masseter, temporal, ptery- 



goids), also the mylohyoid, the tensor palati and the tensor tympani (cf. 

 page 497) and the anterior belly of the inferior digastric. Besides it is stated 

 that the trigeminal contains secretory fibers for the lachrymal glands and the 

 sweat glands of the face, vasodilator fibers for the skin of the face and the 

 eye, etc. 



The afferent fibers of the trigeminal constitute first, the sensory nerves of 

 almost all the skin of the face, of the eye, the nose, the mucous membrane of 

 the mouth, the tongue and the teeth. Secondly, the trigeminal carries a 

 number of nerves of taste (cf. page 484). 



VI. The abducens innervates the external rectus and is said also to con- 

 tain fibers for the sphincter of the pupil. 



VII. The facial, or nerve of expression, contains secretory fibers for the 

 submaxillary, sublingual (cf. page 257) and lachrymal glands, vasodilator 

 fibers for the submaxillary glands and anterior part of the tongue, and motor 

 nerves for the stapedius muscle. Its chief significance, however, is that it 

 innervates the muscles of the face by contraction of which the skin of the face 

 is folded in various ways, producing the different expressions. 



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