NERVOUS SYSTEM. 217 



interest. These two morbid conditions have been considered 

 more in detail elsewhere. 



e. Reflex excitability. Reflex movement is a tem- 

 porary muscular contraction brought about by stimulating a 

 peripheral (sensory) nerve ending. In order that reflex move- 

 ment may occur the sensory and motor nerve fibres and the 

 reflex center must be intact. Reflex movement is limited to one 

 muscle or muscle group (simple reflex) or it may affect the 

 whole body and in that case may be inco-ordinated (reflex 

 spasm) or co-ordinated (motions of defense or flight). The 

 following physiological reflexes are of clinical importance: 



A. Reflexes of the Brain. 



1. Closing of the eyelids. The sensory fibres 

 (trigeminus) of the cornea, conjunctiva and of the skin in 

 the neighborhood of the eye conduct impulses to the medulla 

 oblongata and from that point the facial nerve produces 

 contraction of the orbicularis of the eyelids. 



2. Sensitiveness to light on part of 

 the pupil. Stimulation of the optic nerve is trans- 

 mitted reflexly, to the oculomotorius, which, through con- 

 traction of the sphincter pupillae, cause contraction of the 

 pupil. 



Increased reflex excitability occurs in 

 tetanus and in strychnine poisoning. Contracted pupil is ob- 

 served in morphine, eserine and pilocarpine poisoning. 



Decreased reflex excitability in great 

 mental depression, excessive pain and in dyspnea of high 

 degree. 



Dilated pupil (mydriasis) occurs in paralysis of 

 the optic nerve (black cataract) and in paralysis of the oculo 

 motor nerve (atropin poisoning). 



