592 SIGNIFICANCE OF THE NERVOUS SYSTEM 



orbicular branches of the facial nerve. The effector is the muse, orbicularis 

 palpebrarum. 



(6) Complex reflexes, in which several muscles or secretory units are affected, but 

 the response remains perfectly co-ordinated, in spite of the fact that the effector 

 is now more diversified. As an example of this kind of response might be men- 

 tioned the patellar reflex. The stimulus is applied to the patellar ligament whence 

 the impulse is transferred to the sciatic center by way of the afferent fibers of this 

 nerve. It attains the muscles upon the anterior aspect of the thigh by way of 

 the efferent fibers of the same nerve (ant. crural nerve). 



(c) Spreading reflexes, in which a large number of motor organs are involved. 

 Thus, a certain stimulus may lead to the contraction of many muscles far removed 

 from one another. Their action, however, remains co-ordinated. 



(d) Antagonistic reflexes are made possible by the so-called reciprocal innerva- 

 tion, first described by Sherrington. ^ It frequently happens that the reflex activa- 

 tion of a certain muscle causes at the same time a lessening of the tonus of the cor- 

 responding antagonistic muscle. In a similar way, the relaxation of a previously 

 contracted muscle very frequently incites a contraction of the relaxed antagonistic 

 muscle. This phenomenon is most clearly displayed by the flexors and extensors 

 of the arms and legs, and also by the constrictors and dilators of the iris and other 

 reciprocating effectors. It seems, however, that this reciprocity is not dependent 

 upon a paired arrangement of the peripheral nerves, but upon a peculiar adjustment 

 of the motor centers governing the action of these antagonistic muscles. ^ Appar- 

 ently, their connection is such that the excitation of one motor cell causes the 

 activity of the other to be inhibited. 



(e) Tonic and Spastic Reflexes. — The reaction following a certain stimulus is 

 usually prolonged, and lasts much longer than the stimulus. In many cases, in 

 fact, it assumes so continuous a character that it may be characterized as a true 

 reflex spasm. Experimentally, this peculiarity may be imparted to reflexes very 

 easily by the administration of small doses of strychnin or morphin. It is also a 

 frequent symptom of certain pathologic conditions tending to augment the ir- 

 ritability of the nervous system. A not uncommon reflex of this type is the condi- 

 tion known as blepharospasm, a tonic spasm of the eyelids. 



(/) Periodic and Clonic Reflexes. — In many instances a stimulus may cause a 

 certain response to be repeated a number of times at regular intervals. This is 

 true of the acts of sneezing, coughing, hiccoughing, swallowing, the clattering of 

 the teeth, and trembling. The cremasteric reflex also consists of an often repeated 

 raising and lowering of the testicle. The same is true of the scratching reflex, and 

 of those which may be elicited in decerebrated cats and dogs by tickling the lateral 

 aspect of the abdomen. In many cases, these reactions recur at very brief intervals 

 and assume a prolonged or clonic character. Of especial clinical importance is the 

 ankle clonus, a periodic reflex which may be set up by suddenly flexing the foot 

 and stretching the tendo Achillis. In certain nervous diseases even the patellar 

 reflex may assume a clonic character. 



(g) Alternating reflexes are commonly produced by an alternating activity of 

 antagonistic groups of muscles. Instead of one reaction, a number of them are 

 obtained in orderly sequence. The rocking back and forth of the head upon the 

 trunk may be cited as an example of this type of reflex. In decerebrated animals 

 certain stimuli produce at times an alternate flexion and extension (kicking) of the 

 two posterior extremities. 



{h) Association or Perception Reflexes. — It has previously been stated that the 

 differential sign between a reflex and a reaction is volition. Attention has also 

 been called to the fact that a relatively small number of reflexes necessitate an im- 

 pression in consciousness, otherwise, they cannot fully develop. These actions 

 which skirt the realm of volition without being actually influenced by it, are desig- 



1 The Integrative Action of the Nerve System, Liverpool, 1906. 



2 Ewald, Pfluger's Archiv, xciv, 1903, 46 



