DRUGS ACTING ON THE NERVOUS SYSTEM 45 



(1) Mydriatics. 



(a) ACTING LOCALLY. 



Atropine 



Homatropine 



Hyoscyamine l Paralyse third nerve terminations 



Hyoscine 



Scopolamine 



Gelsemine J 



Cocaine Stimulates sympathetic endings. 



(b) ACTING CENTRALLY. 



Anae^thetips (late in their action) 



The dilating centre is stimulated by carbonic dioxide in 

 the blood, and therefore dilatation of the pupil occurs in 

 asphyxia ; also after irritation of sensory nerves, the sexual 

 organs and digestive apparatus. 



Uses. — Mydriatics are useful in dilating the pupil for 

 examination of the eye, and to prevent adhesions of the iris 

 in central corneal ulcers ; in keratitis, to overcome photo- 

 phobia and bletharospasm ; and in iritis, to secure rest of 

 the iris and ciliary muscles. 



(2) Myotics, 



(a) ACTING LOCALLY. 



Physostigmine ) ^ . 



Pilocarpine j Stimulate third nerve-endmgs 



(b) ACTING CENTRALLY. 



Anaesthetics Opium 



Uses. — Myotics are employed to prevent prolapse. of the 

 iris in wounds and ulcers of the cornea ; to antagonize the 

 effect of atropine ; to prevent the entrance of light in painful 

 disorders of the eye ; to lessen intra-ocular tension in 

 glaucoma ; and, in alternation with mydriatics, to break up 

 adhesions to the iris. All the local mydriatics and myotics 

 mentioned above act on the ciliary muscle to destroy the 

 power of accomodation. Intra-ocular tension in glaucoma 

 is usually increased by atropine and other mydriatics, but is 

 diminished by eserine. 



